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Latest research in football - week 5 - 2020

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Pedagogical Function of Referees in Youth Sport: Assessment of the Quality of Referee-Player Interactions in Youth Soccer
Reference: Int J Environ Res Public Health. 2020 Feb 1;17(3). pii: E905. doi: 10.3390/ijerph17030905.
Authors: Firek W, Płoszaj K, Czechowski M
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Summary: We assume that all institutions and individuals involved in the organization of sport for children and young people should utilize the educational potential of sport. We assessed the quality of referee interactions with children during sports competitions in soccer. Based on the developmental theory and research suggesting that interactions between kids and adults are the primary mechanism of their development and learning, we focused on the quality of the referee-player interactions in terms of (1) emotional support, (2) game organization, and (3) instructional support. Twenty-five soccer referees who refereed matches for children aged 9-12 years were recruited. The Referee Educational Function Assessment Scoring System (REFASS) was used to assess the quality of the referee-player interactions. This tool was developed based on Classroom Assessment Scoring System-Upper Elementary. Regarding the REFASS dimensions, the mean scores for positive climate, Sensitivity, behavior management, content understanding and quality of feedback were in the medium range, while productivity and negative climate in the high range. In the case of the positive climate variable, the lowest mean ratings were recorded compared to other assessed dimensions. The assessments of the quality of referee-player interactions obtained for particular dimensions translated into the ratings for the specified domains. The highest ratings were given to game organization (6.0 ± 0.8; Me = 6.0), whereas the emotional support and instructional support were in the medium range (4.6 ± 1.5; Me = 4.5, and 5.2 ± 1.8; Me = 6.0, respectively). Referees are usually not aware of their pedagogical function and the complexity of their respective responsibilities. They are commonly considered to be ordinary technicians and evaluators of performance in competition. Based on the results, a postulate was formulated that referees should consciously perform a pedagogical function in the youth sport. Therefore, it is necessary to train them in educational methods and techniques appropriate to the age and needs of the child. The referees will then be prepared to take actions to prevent negative behavior of players on the field and to encourage prosocial behavior.

#2 Biomechanical and Physiological Responses to 120 min of Soccer-Specific Exercise
Reference: Res Q Exerc Sport. 2020 Feb 5:1-13. doi: 10.1080/02701367.2019.1698698. [Epub ahead of print]
Authors: Field A, Corr LD, Haines M, Lui S, Naughton R, Page RM, Harper LD
Summary: The purpose of the study is to investigate biomechanical and physiological responses to soccer-specific exercise incorporating an extra-time period (ET) and assess the test-retest reliability of these responses. Twelve soccer players performed 120 min of soccer-specific exercise. Tri-axial (PLTotal) and uni-axial PlayerLoad™ in the vertical (PLV), anterior-posterior (PLA-P), and medial-lateral (PLM-L) planes were monitored using a portable accelerometer. Likewise, respiratory exchange ratio (RER) was recorded throughout exercise. At the end of each 15-min period, players provided differential ratings of perceived exertion for legs (RPE-L), breathlessness (RPE-B) and overall (RPE-O), and capillary samples were taken to measure blood lactate (BLa) concentrations. The soccer-specific exercise was completed twice within 7 days to assess reliability. A main effect for time was identified for PLTotal (p = 0.045), PLV (p = 0.002), PLA-P (p = 0.011), RER (p = 0.001), RPE-L (p = 0.001), RPE-O (p = 0.003), and CMJ (p = 0.020). A significant increase in PLTotal (234 ± 34 au) and decrease in RER (0.87 ± 0.03) was evident during 105-120 versus 0-15 min (215 ± 25 au; p = 0.002 and 0.92 ± 0.02; p = 0.001). Coefficients of variations were <10% and Pearson's correlation coefficient demonstrated moderate-to-very strong (0.33-0.99) reliability for all PL variables, RPE-B, BLa, and RER. These results suggest that mechanical efficiency is compromised and an increased rate of lipolysis is observed as a function of exercise duration, particularly during ET. These data have implications for practitioners interested in fatigue-induced changes during ET.

#3 Constraints on visual exploration of youth football players during 11v11 match-play: The influence of playing role, pitch position and phase of play
Reference: J Sports Sci. 2020 Feb 2:1-11. doi: 10.1080/02640414.2020.1723375. [Epub ahead of print]
Authors: McGuckian TB, Cole MH, Chalkley D, Jordet G, Pepping GJ
Summary: Visual exploratory action, in which football players turn their head to perceive their environment, improves prospective performance with the ball during match-play. This scanning action, however, is relevant for players throughout the entire match, as the information perceived through visual exploration is needed to guide movement around the pitch during both offensive and defensive play. This study aimed to understand how a player's on-pitch position, playing role and phase of play influenced the visual exploratory head movements of players during 11v11 match-play. Twenty-two competitive-elite youth footballers (M = 16.25 years) played a total of 1,623 minutes (M = 73.8). Inertial measurement units, global positioning system units and notational analysis were used to quantify relevant variables. Analyses revealed that players explored more extensively when they were in possession of the ball, and less extensively during transition phases, as compared to team ball-possession and opposition ball-possession phases of play. Players explored most extensively when in the back third of the pitch, and least when they were in the middle third of the pitch. Playing role, pitch position and phase of play should be considered as constraints on visual exploratory actions when developing training situations aimed at improving the scanning actions of players.

#4 Analyzing the effects of combined small-sided games and strength and power training on the fitness status of under-19 elite football players
Reference: J Sports Med Phys Fitness. 2020 Jan;60(1):1-10. doi: 10.23736/S0022-4707.19.09818-9.
Authors: Querido SM, Clemente FM
Summary: The purpose of this study was twofold: 1) to characterize a common microcycle considering both internal and external training loads; and 2) to identify the effects of small-sided games (SSGs) and of power and strength training on the fitness status of football players. Fifteen male football players (age: 18.55±0.39 years) participated in this study. Ninety-two consecutive training sessions were monitored and analyzed over a period of nineteen weeks. Rating of perceived exertion (RPE ) was used as an internal load marker, and the distances covered at different speed thresholds and accelerations/decelerations were used as external load markers to characterize the common microcycle. Participants' body composition, vertical jumping ability, maximal strength, speed, and agility were assessed twice before and after the training monitoring process. The results revealed that match day -5 (MD-5) and MD-1 were associated with the lowest RPE scores (4.2 and 3.8 A.U., respectively). MD-4 and MD-3 were associated with the highest RPE values (9.2 and 8.8 A.U., respectively). Meaningful changes in RPE were found between training days. External load monitoring revealed that MD-4 had the highest values of accelerations and decelerations >2 m/s2/min (4.22 and 3.17, respectively) and MD-3 had the highest values of distance covered at high intensity (6.11 m/s2/min). Meaningful moderate improvements in jumping performance (d=0.90) and maximal strength parameters (d=0.83) were also found between assessments. It was identified that the concurrent approach had meaningful impacts on the fitness development of players and should be considered by coaches for future training interventions.

#5 Soccer Matches but Not Training Sessions Disturb Cardiac-Autonomic Regulation During National Soccer Team Training Camps
Reference: Res Q Exerc Sport. 2020 Feb 6:1-9. doi: 10.1080/02701367.2019.1708843. [Epub ahead of print]
Authors: Muñoz-López A, Nakamura F, Naranjo Orellana J
Summary: Heart rate variability (HRV) can be used to monitor changes in autonomic nervous system (ANS) function. Monitoring HRV via the natural log of the root-mean-square difference of successive normal RR intervals (lnRMSSD), a decrease was related to lower parasympathetic activity and a fatigued state, and an increase was related to higher parasympathetic activity and better physical conditioning. This study analyzed daily ANS function changes among professional soccer players at national team training camps during preparation for the UEFA Eurocup 2016. 23 professional soccer players were distributed into two groups: First eleven (players who played more than 60 minutes per soccer match) and Reserves (the rest of the players). HRV and session training load (s-TL) were monitored. Between-group daily differences were assessed using two-way mixed repeated measures ANOVA. s-TL significantly increased (p < .05) at the beginning of each camp and significantly decreased the day before the soccer match (p < .001). There was a significant time by group interaction in lnRMSSD (p = .024). Changes were found in the First eleven group from match day +1 to match day +2 (+0.523 ms, p = .003). After the soccer match, there were between-group differences (p < .05) at +24h and +72h in lnRMSSD. During national team training camps, ANS function was only modified 24h and 72h after playing soccer matches, in players who played a minimum of 60 minutes. This knowledge can help coaches to monitor the impact of soccer matches during training camps to detect fatigue and improve recovery.

#6 Global and region-specific patient-reported outcomes pre and post a division I football season
Reference: Phys Ther Sport. 2020 Jan 25;42:146-150. doi: 10.1016/j.ptsp.2020.01.014. [Epub ahead of print]
Authors: Parcell B, Simon JE
Summary: Determine the change in global and region-specific PROMs among athletes from one NCAA Division I football team during one season. Fifty-three Division I collegiate football athletes (n = 54) were eligible (20.1 ± 1.4 years, 187.7 ± 8.3 cm, and 113.5 ± 25.6 kg) for analyses participated in this study. Participants completed five PROMs (Disablement in the Physically Active Scale [DPA], Epworth Sleep Score [ESS], Headache Impact Test [Hit-6], Disabilities of the Arm, Shoulder, and Hand [DASH], and the Lower Extremity Functional Scale [LEFS]) before the season and the same five PROMs after the season. A multivariate repeated measure analysis of variance (ANOVA) was conducted for all dependent variables. Alpha level was set at ɑ = 0.05. The overall multivariate repeated measures ANOVA was significant for time (p = 0.01). Follow up one-way ANOVA's indicated the DPA (p < 0.01, mean decrease/worse of 6.6 points) and LEFS (p = 0.01, mean decrease/worse of 4.1 points) were statistically significant between time points. Division I football can be detrimental to the physical, mental, and emotional health of the athletes. From these data, global and one region-specific PROM decreased over one season in one NCAA Division I football team.

#7 Understanding the relative contribution of technical and tactical performance to match outcome in Australian Football
Reference: J Sports Sci. 2020 Feb 7:1-6. doi: 10.1080/02640414.2020.1724044. [Epub ahead of print]
Authors: Young CM, Luo W, Gastin PB, Dwyer DB
Summary: The aim of this study was to assess if tactical and technical performance indicators (PIs) could be used in combination to model match outcomes in Australian Football (AF). A database of 101 technical PIs and 14 tactical PIs from every match in the 2009-2016 Australian Football League (AFL) seasons was merged. Two outcome measures Win-loss and Score margin were used as dependent variables. The top 45 ranked technical and tactical PIs from a feature selection process were used to model match outcome using decision tree and Generalised Linear Models (GLMs). Of the top 45 selected features, this included seven tactical PIs. The Win-loss-based Decision tree model achieved a classification accuracy of 89.0% and GLM 93.2%. A Score margin-based GLM achieved a root mean squared error (RMSE) of 6.9 points. A combined approach to the classification of match outcomes provided no improvement in model accuracy compared with previous literature. However, this study has established the relative importance of technical and tactical measures of performance in relation to successful team performance in AF.

#8 Reproducibility of Internal and External Training Load During Recreational Small-Sided Football Games
Reference: Res Q Exerc Sport. 2020 Feb 5:1-6. doi: 10.1080/02701367.2019.1697794. [Epub ahead of print]
Authors: Milanović Z, Rađa A, Erceg M, Trajković N, Stojanović E, Lešnik B, Krustrup P, Randers MB
Summary: The aim of this study was to evaluate the reproducibility of internal and external load parameters during recreational small-sided football games. Ten healthy untrained young adult males (age: 20.2 ± 1.9 yr, body mass: 69.2 ± 6.3 kg, height: 175.4 ± 5.9 cm, body fat: 19.7 ± 5.2%) performed two 2 × 20-min sessions of four versus four plus goalkeeper small-sided games (SSG) 1 week apart on a standard, outdoor, 40 × 20-m artificial grass pitch. Twelve external (total distance, peak speed, player load, work rate and distance covered at 0-2, 2-5, 5-7, 7-9, 9-13, 13-16, 16-20 and >20 km/h) and seven internal load parameters (heart rate and time spent in different heart rate zones [<70%, 71-80%, 81-90%, 91-95%, 96-100%, 91-100%]) were measured. Reproducibility was reported as intraclass coefficient correlation (ICC), the coefficient of variation (CV), and the typical error of measurements (TE). No statistical differences (p> .05) between sessions were found in any measures. Minimal test-retest variability was noted for mean and peak heart rate (HRpeak) relative to HRpeak with CV values of 3.4% and 2.6%, respectively. Acceptable variability (CV<10%) was demonstrated for total distance covered, distance covered at 2-5 km/h, and peak speed. Distance covered in different speed zones (CV = 15.7-47.6%) and percentage of time in each HR zone showed large-to-very large variability (CV = 36.2-128.4%). Mean heart rate (HRmean), HRpeak, distance covered at 5-7, 13-16 and >20 km/h, and percentage of time above 95%HRpeak were the most reliable variables (ICC = 0.74-0.79), followed by total distance covered, peak speed, and percentage of time at 80-90% HRpeak (ICC = 0.39-0.67). The lowest reliability was observed for distance covered in the moderate speed zones 7-9 km/h (ICC = 0.12) and 9-13 km/h (ICC = -0.09), and percentage of time at 70-80% HRpeak (ICC = -0.01). Small-sided games can be used when planning training-induced exercise responses in relation to total distance covered, peak speed, and mean heart rate. This evidence further supports the use of SSG when organizing recreational football training, in young adult males, with the purpose of improving health profile due to the high reproducibility of HRmean and total distance covered.

#9 Uncovering EEG Correlates of Covert Attention in Soccer Goalkeepers: Towards Innovative Sport Training Procedures
Reference: Sci Rep. 2020 Feb 3;10(1):1705. doi: 10.1038/s41598-020-58533-2.
Authors: Jeunet C, Tonin L, Albert L, Chavarriaga R, Bideau B, Argelaguet F, Millán JDR, Lécuyer A, Kulpa R
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Summary: Advances in sports sciences and neurosciences offer new opportunities to design efficient and motivating sport training tools. For instance, using NeuroFeedback (NF), athletes can learn to self-regulate specific brain rhythms and consequently improve their performances. Here, we focused on soccer goalkeepers' Covert Visual Spatial Attention (CVSA) abilities, which are essential for these athletes to reach high performances. We looked for Electroencephalography (EEG) markers of CVSA usable for virtual reality-based NF training procedures, i.e., markers that comply with the following criteria: (1) specific to CVSA, (2) detectable in real-time and (3) related to goalkeepers' performance/expertise. Our results revealed that the best-known EEG marker of CVSA-increased α-power ipsilateral to the attended hemi-field- was not usable since it did not comply with criteria 2 and 3. Nonetheless, we highlighted a significant positive correlation between athletes' improvement in CVSA abilities and the increase of their α-power at rest. While the specificity of this marker remains to be demonstrated, it complied with both criteria 2 and 3. This result suggests that it may be possible to design innovative ecological training procedures for goalkeepers, for instance using a combination of NF and cognitive tasks performed in virtual reality.

#10 Prevalence of Asymptomatic Intra-articular Changes of the Knee in Adult Professional Soccer Players
Reference: Orthop J Sports Med. 2019 Nov 27;7(11):2325967119885370. doi: 10.1177/2325967119885370. eCollection 2019 Nov.
Authors: Bezuglov EN, Lyubushkina AV, Khaitin VY, Tokareva AV, Goncharov EN, Gorinov AV, Sivakova EY, Sereda AP
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Summary: Currently, there are few data on the association between participation in soccer and the condition of the knee joints in adult professional players. The hypothesis was that a high percentage of professional soccer players will have asymptomatic intra-articular changes of the knee. The condition of the intra-articular structures (osteophytes, cartilage, and menisci) in 94 knee joints of 47 adult professional soccer players (mean ± SD age, 25.7 ± 4.6 years; body mass index, 22.8 ± 1.4 kg/m2) was analyzed. A 1.5-T magnetic resonance imaging scanner was used to perform the imaging, and the anonymized data were analyzed by 2 experienced radiologists. Cartilage of both knee joints was affected in 97.9% of soccer players. Meniscal lesions were detected in 97.8% of joints, affecting both joints in 93.6% of athletes. Grade 2 cartilage lesions were the most prevalent (36%-60% depending on the lesion site), and grade 4 lesions were detected in 12.7% of joints. The medial femoral condyle and medial tibial plateau were most frequently affected by cartilage lesions (85.1%). Among meniscal lesions, grade 2 lesions were the most prevalent, being detected in 71% of the cases. Grade 3 lesions were detected in 13.8% of the joints. The posterior horn of the lateral meniscus was the most common site of meniscal lesions (affected in 95.7% of the joints). Osteophytes were detected in 4.2% of joints. The prevalence of asymptomatic cartilage and meniscal lesions in the knees of adult professional soccer players is extremely high and is not associated with the reduction of sports involvement. This research should promote the correct interpretation of magnetic resonance imaging data obtained from soccer players with acute trauma and the reduction of the number of unwarranted surgical procedures.

#11 Injury epidemiology in Australian male professional soccer
Reference: J Sci Med Sport. 2020 Jan 24. pii: S1440-2440(19)31442-2. doi: 10.1016/j.jsams.2020.01.006. [Epub ahead of print]
Authors: Lu D, McCall A, Jones M, Kovalchik S, Steinweg J, Gelis L, Duffield R
Summary: The purpose was to describe the injury epidemiology of the Australian male professional soccer league (A-League) over 6 consecutive seasons. Match-loss injury data was collected from each A-League club (n=10) for each competition match (n=27/season) over 6 seasons (2012/13-2017/18). Injuries were collected weekly through a standardised protocol and were classified by setting, mechanism, severity, the type and location on the body. Generalised Linear Models were used to estimate the injury incidences (injury/round/season), whilst rate ratios were reported for total injuries and within abovementioned injury classifications. Overall injury incidence was not significantly different ranging from 4.8 (95%CI:4.1-5.8) to 6.7 (95%CI:5.8-7.8) between seasons 2012/13 to 2017/18 (p>0.05). Match injuries remained stable whilst training injuries decreased across the 6 seasons (exp(β) 0.59[95%CI:0.36-1.0]; p=0.04). Respectively, contact and non-contact injuries were not significantly different across the 6 seasons, although non-contact injuries were more common than contact injuries (p>0.05). Mild severity injuries decreased (exp(β) 0.64 [95%CI:0.4-0.9];p=0.02), whilst moderate severity injuries increased (exp(β) 1.7 [95%CI:1.0-2.8];p=0.04) in season 2017/18 compared to 2012/13. The most common injuries were at thigh (23-36%), of which the majority were hamstring injuries (54%-65%) of muscle/tendon type (50-60% of total injuries/season). Injuries remained stable across the seasons by type and location (p>0.05 and p>0.05, respectively). Injury rates, mechanisms, locations and types have remained relatively stable over recent seasons of the A-League. Current Australian professional soccer league medical practices may have contributed to the stability of injury rates.





Latest research in football - week 4 - 2020

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Train Like You Compete? Physical and Physiological Responses on Semi-Professional Soccer Players
Reference: Int J Environ Res Public Health. 2020 Jan 24;17(3). pii: E756. doi: 10.3390/ijerph17030756.
Authors: Castillo-Rodríguez A, Cano-Cáceres FJ, Figueiredo A, Fernández-García JC
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Summary: Decision-making in soccer has repercussions and depends on the environment of training or competition. The demands on the players can reveal if the decision-making is similar or different from that required during competition. The aim of this study was to assess the physical and physiological responses of players in training matches (TM) and official competition matches (CM) according to the playing position (external defenders, internal defenders, midfielders, and forwards/extremes). Twenty semi-professional male soccer players and 10 CM (n = 40) and 10 TM (n = 40) were studied using global positioning system technology, and paired and one-way ANOVA tests were carried out to compare physical (distances and number of sprints) and physiological (heart rates) responses with the factors a) match environments (TM and CM) and b) the playing position, respectively. The results revealed that during CM, players covered higher total distance, partial distances, and sprints at different speeds (0-21 km/h) and produced higher physiological responses. Midfielders covered the greatest total distance in both TM (7227.6 m) and CM (11,225.9 m), in comparison to the other playing positions. However, forwards and extremes spent more time (56.8% of the CM [d = 0.78]) at 76% to 84% of their maximal heart rates. First, the physical and physiological responses in TM were significantly lower than in CM. Second, these responses were different according to the playing position, so this study was able to verify the exact amount of variation between the load produced in TM and CM. These results will help the coach and technical staff to design training tasks to complement the responses found in TM.

#2 T helper cell-related changes in peripheral blood induced by progressive effort among soccer players
Reference: PLoS One. 2020 Jan 28;15(1):e0227993. doi: 10.1371/journal.pone.0227993. eCollection 2020.
Authors: Kostrzewa-Nowak D, Nowak R
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Summary: The regulatory mechanisms affecting the modulation of the immune system accompanying the progressive effort to exhaustion, particularly associated with T cells, are not fully understood. We analysed the impact of two progressive effort protocols on T helper (Th) cell distribution and selected cytokines. Sixty-two male soccer players with a median age of 17 (16-29) years performed different protocols for progressive exercise until exhaustion: YO-YO (YYRL1) and Beep. Blood samples for all analyses were taken three times: at baseline, post-effort, and in recovery. The percentage of Th1 cells increased post-effort and in recovery. The post-effort percentage of Th1 cells was higher in the Beep group compared to the YYRL1 group. Significant post-effort increase in Th17 cells was observed in both groups. The post-effort percentage of regulatory T cells (Treg) increased in the Beep group. An increased post-effort concentration of IL-2, IL-6, IL-8 and IFN-γ in both groups was observed. Post-effort TNF-α and IL-10 levels were higher than baseline in the YYRL1 group, while the post-effort IL-17A concentration was lower than baseline only in the Beep group. The recovery IL-2, IL-4, TNF-α and IFN-γ levels were higher than baseline in the YYRL1 group. The recovery IL-4, IL-6, IL-8, TNF-α and IFN-γ values were higher than baseline in the Beep group. The molecular patterns related to cytokine secretion are not the same between different protocols for progressive effort. It seems that Treg cells are probably the key cells responsible for silencing the inflammation and enhancing anti-inflammatory pathways

#3 Are Elite Soccer Teams' Preseason Training Sessions Associated With Fewer In-Season Injuries? A 15-Year Analysis From the Union of European Football Associations (UEFA) Elite Club Injury Study
Reference: Am J Sports Med. 2020 Jan 28:363546519899359. doi: 10.1177/0363546519899359. [Epub ahead of print]
Authors: Ekstrand J, Spreco A, Windt J, Khan KM
Summary: Preseason training develops players' physical capacities and prepares them for the demands of the competitive season. In rugby, Australian football, and American football, preseason training may protect elite players against in-season injury. However, no study has evaluated this relationship at the team level in elite soccer. The aim of this study was to investigate whether the number of preseason training sessions completed by elite soccer teams was associated with team injury rates and player availability during the competitive season. It was hypothesized that elite soccer teams who participate in more preseason training will sustain fewer injuries during the competitive season. We used the Union of European Football Associations (UEFA) injury dataset to analyze 44 teams for up to 15 seasons (total, 244 team-seasons). Separate linear regression models examined the association between the number of team preseason training sessions and 5 in-season injury measures. Injury-related problems per team were quantified by totals of the following: (1) injury burden, (2) severe injury incidence, (3) training attendance, (4) match availability, and (5) injury incidence. Teams averaged 30 preseason training sessions (range, 10-51). A greater number of preseason training sessions was associated with less injury load during the competitive season in 4 out of 5 injury-related measures. Our linear regression models revealed that for every 10 additional preseason training sessions that the team performed, the in-season injury burden was 22 layoff days lower per 1000 hours (P = .002), the severe injury incidence was 0.18 severe injuries lower per 1000 hours (P = .015), the training attendance was 1.4 percentage points greater (P = .014), and the match availability was 1.0 percentage points greater (P = .042). As model fits were relatively low (adjusted R2 = 1.3%-3.2%), several factors that contribute to in-season injury outcomes were unaccounted for. Teams that performed a greater number of preseason training sessions had "healthier" in-season periods. Many other factors also contribute to in-season injury rates. Understanding the benefit of preseason training on in-season injury patterns may inform sport teams' planning and preparation.

#4 Effects of Small-Sided Soccer Games on Physical Fitness, Physiological Responses, and Health Indices in Untrained Individuals and Clinical Populations: A Systematic Review
Reference: Sports Med. 2020 Jan 27. doi: 10.1007/s40279-019-01256-w. [Epub ahead of print]
Authors: Zouhal H, Hammami A, Tijani JM, Jayavel A, de Sousa M, Krustrup P, Sghaeir Z, Granacher U, Ben Abderrahman A
Summary: Small-sided soccer games (SSSG) are a specific exercise regime with two small teams playing against each other on a relatively small pitch. There is evidence from original research that SSSG exposure provides performance and health benefits for untrained adults. The aim of this systematic review was to summarize recent evidence on the acute and long-term effects of SSSG on physical fitness, physiological responses, and health indices in healthy untrained individuals and clinical populations. This systematic literature search was conducted in four electronic databases (PubMed, Web of Science, SPORTDiscus) from inception until June 2019. The following key terms (and synonyms searched for by the MeSH database) were included and combined using the operators "AND", "OR", "NOT": ((soccer OR football) AND ("soccer training" OR "football training" OR "soccer game*" OR "small-sided soccer game*") AND ("physical fitness" OR "physiological adaptation*" OR "physiological response*" OR health OR "body weight" OR "body mass" OR "body fat" OR "bone composition" OR "blood pressure")). The search syntax initially identified 1145 records. After screening for titles, abstracts, and full texts, 41 studies remained that examined the acute (7 studies) and long-term effects (34 studies) of SSSG-based training on physical fitness, physiological responses, and selected alth indices in healthy untrained individuals and clinical populations. No training-related injuries were reported in the 41 acute and long-term SSSG studies. Typically, a single session of SSSG lasted 12-20 min (e.g., 3 × 4 min with 3 min rest or 5 × 4 min with 4 min rest) involving 4-12 players (2 vs. 2 to 6 vs. 6) at an intensity ≥ 80% of HRmax. Following single SSSG session, high cardiovascular and metabolic demands were observed. Specifically, based on the outcomes, the seven acute studies reported average heart rates (HR) ≥ 80% of HRmax (165-175 bpm) and mean blood lactate concentrations exceeding 5 mmol/l (4.5-5.9 mmol/l) after single SSSG sessions. Based on the results of 34 studies (20 with healthy untrained, 10 with unhealthy individuals, and 4 with individuals with obesity), SSSG training lasted between 12 and 16 weeks and was performed 2-3 times per week. SSSG had positive long-term effects on physical fitness (e.g., Yo-Yo IR1 performance), physiological responses including maximal oxygen uptake (VO2max) [+ 7 to 16%], and many health-related markers such as blood pressure (reductions in systolic [- 7.5%] and diastolic [- 10.3%] blood pressure), body composition (decreased fat mass [- 2 to - 5%]), and improved indices of bone health (bone mineral density: [+ 5 to 13%]; bone mineral content: [+ 4 to 5%]), and metabolic (LDL-cholesterol [- 15%] as well as cardiac function (left-ventricular internal diastolic diameter [+ 8%], end diastolic volume [+ 21%], left-ventricular mass index [+ 18%], and left-ventricular ejection fraction [+ 8%]). Irrespective of age or sex, these health benefits were observed in both, untrained individuals and clinical populations. In conclusion, findings from this systematic review suggest that acute SSSG may elicit high cardiovascular and metabolic demands in untrained healthy adults and clinical populations. Moreover, this type of exercise is safe with positive long-term effects on physical fitness and health indices. Future studies are needed examining the long-term effects on physical fitness and physiological adaptations of different types of SSSG training (e.g., 3 vs. 3; 6 vs. 6) in comparison to continuous or interval training in different cohorts.

#5 Pubic stress fracture presenting as a strain of adductor longus in a 16-year-old elite soccer player with Crohn's disease: a case report
Reference: J Can Chiropr Assoc. 2019 Dec;63(3):197-204.
Authors: Marshall C, Gringmuth R
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Summary: Adductor strains are the most commonly reported muscle injuries in adolescent soccer players and the second most common muscle injuries in adult players. Health practitioners should be aware of possible differential diagnoses, such as a pubic stress fracture or pubic apophysitis when athletes present with chronic groin pain. The purpose was to present a rare case of a unilateral pelvic stress fracture of a 16-year old elite soccer player with a history of Crohn's disease. Case notes of two sports-based practitioners were reviewed and compiled retrospectively. Following activity restriction, a period of rest, conservative care, and progressive rehabilitation, this athlete was able to achieve a pain-free state with near equal iso-kinetic strength bilaterally as measured by Cybex 6000 (Cybex International Inc., Medway, MA, USA) muscle testing. Full activity was resumed 10 months after initial presentation and the athlete was able to return to playing professional soccer. This case report presents a rare diagnosis of a unilateral pubic stress fracture presenting as a strain of adductor longus. Although quite rare, differential diagnoses such as a potential underlying stress fracture should be considered when presented with chronic or recurrent groin pain.

#6 Associations of Apolipoprotein E ε4 Genotype and Ball Heading With Verbal Memory in Amateur Soccer Players
Reference: JAMA Neurol. 2020 Jan 27. doi: 10.1001/jamaneurol.2019.4828. [Epub ahead of print]
Authors: Hunter LE, Freudenberg-Hua Y, Davies P, Kim M, Lipton RB, Stewart WF, Srinivasan P, Hu S, Lipton ML
Summary: Emerging evidence suggests that long-term exposure to ball heading in soccer, the most popular sport in the world, confers risk for adverse cognitive outcomes. However, the extent to which the apolipoprotein E ε4 (APOE ε4) allele, a common risk factor for neurodegeneration, and ball heading are associated with cognition in soccer players remains unknown. The purpose was to determine whether the APOE ε4 allele and 12-month ball heading exposure are associated with verbal memory in a cohort of adult amateur soccer players. A total of 379 amateur soccer players were enrolled in the longitudinal Einstein Soccer Study from November 11, 2013, through January 23, 2018. Selection criteria included participation in soccer for more than 5 years and for more than 6 months per year. Of the 379 individuals enrolled in the study, 355 were genotyped. Three players were excluded for reporting extreme levels of heading. Generalized estimating equation linear regression models were employed to combine data across visits for a cross-sectional analysis of the data. At each study visit every 3 to 6 months, players completed the HeadCount 12-Month Questionnaire, a validated, computer-based questionnaire to estimate 12-month heading exposure that was categorized as low (quartiles 1 and 2), moderate (quartile 3), and high (quartile 4). Verbal memory was assessed at each study visit using the International Shopping List Delayed Recall task from CogState was used as outcome measures.  A total of 352 soccer players (256 men and 96 women; median age, 23 years [interquartile range, 21-28 years]) across a total of 1204 visits were analyzed. High levels of heading were associated with worse verbal memory performance (β = -0.59; 95% CI, -0.93 to -0.25; P = .001). There was no main association of APOE ε4 with verbal memory (β = 0.09; 95% CI, -0.24 to 0.42; P = .58). However, there was a significant association of APOE ε4 and heading with performance on the ISRL task (χ2 = 7.22; P = .03 for overall interaction). In APOE ε4-positive players, poorer verbal memory associated with high vs low heading exposure was 4.1-fold greater (APOE ε4 negative, β = -0.36; 95% CI, -0.75 to 0.03; APOE ε4 positive, β = -1.49; 95% CI, -2.05 to -0.93), and poorer verbal memory associated with high vs moderate heading exposure was 8.5-fold greater (APOE ε4 negative, β = -0.13; 95% CI, -0.54 to 0.29; APOE ε4 positive, β = -1.11, 95% CI, -1.70 to -0.53) compared with that in APOE ε4-negative players. This study suggests that the APOE ε4 allele is a risk factor for worse memory performance associated with higher heading exposure in the prior year, which highlights that assessing genetic risks may ultimately play a role in promoting safer soccer play.

#7 Effects of Soccer Match-Play on Unilateral Jumping and Interlimb Asymmetry: A Repeated-Measures Design
Reference: J Strength Cond Res. 2020 Jan 24. doi: 10.1519/JSC.0000000000003389. [Epub ahead of print]
Authors: Bishop C, Read P, Stern D, Turner A
Summary: The aims of this study were two-fold: (a) determine the effects of repeated soccer match-play on unilateral jump performance and interlimb asymmetries and (b) examine associations between asymmetry and commonly reported external load variables collected during competition. Single-leg countermovement jumps and drop jumps were collected before and immediately after 5 soccer matches in elite academy soccer players. Global positioning system data were also collected during each match as part of the routine match-day procedures. Single-leg countermovement jump height and concentric impulse showed significant reductions after matches (p < 0.01; effect size [ES]: -0.67 to -0.69), but peak force did not (p > 0.05; ES: -0.05 to -0.13). Single-leg drop jump height and reactive strength also showed significant reductions after matches (p < 0.01; ES: -0.39 to -0.58). No meaningful reductions in asymmetry were present at the group level, but individual responses were highly variable. Significant associations between postmatch reactive strength asymmetry and explosive distance (r = 0.29; p < 0.05), relative explosive distance (r = 0.34; p < 0.05), high-speed running (r = 0.35; p < 0.05), and relative high-speed running (r = 0.44; p < 0.01) were observed. These findings show that unilateral jump tests are more appropriate than asymmetry to detect real change after soccer competition, and practitioners should be cautious about using asymmetry to inform decision-making during the temporal recovery period.

#8 Maturity Related Differences in Body Composition Assessed by Classic and Specific Bioimpedance Vector Analysis among Male Elite Youth Soccer Players
Reference: Int J Environ Res Public Health. 2020 Jan 22;17(3). pii: E729. doi: 10.3390/ijerph17030729.
Authors: Toselli S, Marini E, Maietta Latessa P, Benedetti L, Campa F
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Summary: The aim of this study was to analyze the efficiency of classic and specific bioelectrical impedance vector analysis (BIVA) in the assessment of maturity related differences in body composition among male elite youth soccer players, and to provide bioelectrical impedance reference data for this category. A group of 178 players (aged 12.1 ± 1.6 years) were registered in a professional Italian soccer team participating in the first division (Serie A). They were divided into three groups according to their maturity status while bioelectrical resistance and reactance were obtained. The classic and specific BIVA procedures were applied, which correct bioelectrical values for body height and body geometry, respectively. Percentage of fat mass (FM%) and total body water (TBW (L)) were estimated from bioelectrical values. Age-specific z-scores of the predicted age at peak height velocity identified 29 players as earlier-, 126 as on time-, and 23 as later-maturing. TBW was higher (p < 0.01) in adolescents classified as "early" maturity status compared to the other two groups and classic BIVA confirmed these results. Conversely, no differences in FM% were found among the groups. Specific vector length showed a higher correlation (r = 0.748) with FM% compared with the classic approach (r = 0.493). Classic vector length showed a stronger association (r = -0.955) with TBW compared with specific (r = -0.263). Specific BIVA turns out to be accurate for the analysis of FM% in athletes, while classic BIVA shows to be a valid approach to evaluate TBW. An original data set of bioelectric impedance reference values of male elite youth soccer players was provided.

#9 Spatio-temporal investigation of surface soil hardness on professional football field
Reference: Environ Monit Assess. 2020 Jan 30;192(2):151. doi: 10.1007/s10661-020-8087-7.
Authors: Biraderoglu M, Kaplan S, Basaran M
Summary: The present study was conducted to identify the minimum number of sampling points to monitor surface hardness of the pitches through geostatistical methods and to determine spatial and temporal distribution of surface hardness in autumn, winter, spring, and summer periods. Initial samplings were performed from 126 points and with data reduction, the optimum number of sampling points was identified as 77. In upcoming sampling periods, surface hardness and soil temperature were directly measured in situ and disturbed soil samples taken from 77 points were subjected to moisture content, bulk density, and texture analyses (clay-C, silt-Si, and sand-S). In autumn period, surface hardness highly correlated with soil temperature and moisture content (r2 = - 0.438 and - 0.344, p < 0.01). Surface hardness significantly correlated only with soil temperature in winter period and only with bulk density in summer period (respectively r2 = - 0.366 and 0.234, p < 0.01). Average surface hardness values in autumn, winter, spring, and summer periods were respectively measured as 5.99, 6.55, 5.84, and 5.92%. Semivariograms generated for hardness were modeled with spherical model in all periods and a certain nugget effect was detected in all periods. Maximum likelihood distance for autumn, winter, spring, and summer periods was respectively measured as 65, 40, 45, and 46 m. It was concluded based on present findings that geostatistical methods could reliably be used to monitor surface hardness of football pitches and then proper and timely interventions could be made to sections not complying with FIFA standards.

#10 The Influence of Time of Season on Injury Rates and the Epidemiology of Canadian Football Injuries
Reference: Clin J Sport Med. 2020 Feb 6. doi: 10.1097/JSM.0000000000000824. [Epub ahead of print]
Authors: Robbins SM, Bodnar C, Donatien P, Mirza R, Zhao ZY, Hoeber S, Naidu D, Redelmeier A, Steele RJ, Shrier I
Summary: The purpose was to describe injury rates and injury patterns in the Canadian Football League (CFL) according to time during the season, player position, injury type, and injury location. Depending on the analysis, time of season (preseason, regular, and playoffs), player position, injury type, and injury location. Medical attention and time-loss injury rates per 100 athletes at risk (AAR), and prevalence of time-loss injuries per week. The average game injury rate was 45.2/100 AAR medical attention injuries and 30.7/100 AAR time-loss injuries. Injury rates declined by 1% per week over the season for both medical attention (rate ratio = 0.99) and time-loss (rate ratio = 0.99) injuries, with a substantial decline during the playoffs compared with preseason (rate ratio = 0.70-0.77). The number of ongoing time-loss injuries increased over the course of the regular season. Quarterbacks, offensive backs, and linebackers had the highest game injury rates. Joint/ligament and muscle/tendon injuries were the most common injury types for games and practices, respectively. The lower extremity was the most commonly affected area, specifically the lower leg/ankle/foot and hip/groin/thigh. There was a 1% decline in injury rate per week during the season and a 30% decline during the playoffs. The number of ongoing time-loss injuries increased over the regular season. Current results can aid league officials and medical staff in making evidence-based decisions concerning player safety and health.

#11 A systematic review of genitourinary injuries arising from rugby and football
Reference: J Pediatr Urol. 2020 Jan 7. pii: S1477-5131(19)30443-7. doi: 10.1016/j.jpurol.2019.12.019. [Epub ahead of print]
Authors: Kim JK, Koyle MA, Lee MJ, Nason GJ, Ren LY, O'Kelly F
Summary: Genitourinary injuries in athletes engaging in high-impact sports such as football and rugby may have catastrophic consequences, especially in individuals with pre-existing urologic concerns, such as a solitary kidney. The purpose was to summarize the current literature on football-related or rugby-related genitourinary organ injuries in both adult and pediatric populations in an effort to risk stratify the likelihood of these injuries. An independent systematic literature search for records reporting football-related or rugby-related injuries was conducted by a certified librarian and reviewer in March 2019. The search electronic databases included Medline, EMBASE, Scopus, and Web of Science. All studies reporting football-related or rugby-related genitourinary injuries were included. Twenty-two records (11 research studies, 11 case reports) were identified. In the pediatric population, the reported football-related kidney injuries were 0.1-0.7% of all football-related injuries, 0.07-0.5% of all sports-related injuries, and 1.5-37.5% of all sports-related genitourinary injuries, with incidence ranging from 0.00000084 to 0.0000092 injuries per exposure (five studies). Pediatric football-related testicular injuries were reported to be 0.11% of all football injuries, 0-0.07% of all sports-related injuries, and 0-37.5% of all sports-related genitourinary injuries; injury per exposure was 0.0000092 (four studies). In adults, there was no proportion of genitourinary injuries that could be determined, and football-related kidney injury incidence was 0.000012 injuries per exposure (one study). No adult literature investigated testicular injuries. Eleven case reports were additionally identified. Review of the case reports suggests that patients with previously existing urologic abnormalities such as ureteropelvic junction obstruction may predispose an individual to kidney injuries. There is little to suggest that those engaged in football or rugby have a significant risk of genitourinary injury; therefore, future guidelines should reflect this.

#12 Injury in elite women's soccer: a systematic review
Reference: Phys Sportsmed. 2020 Feb 6:1-7. doi: 10.1080/00913847.2020.1720548. [Epub ahead of print]
Authors: Alahmad TA, Kearney P, Cahalan R
Summary: The objective was to summarize risk factors for injury in elite women's soccer. Ten electronic databases were searched for studies that explored risk factors for injury in elite women soccer players. Study cohorts were required to consist of adult (?18 years) elite players defined as 'the best performers in their country in a certain sport who are competing at national or international levels' [1]. Two reviewers independently assessed articles for eligibility. The CASP checklist was used for quality assessment of included studies, and the Oxford Center of Evidence-Based Medicine guidelines were used to determine their level of evidence. Eight studies were included in this review. Findings indicated an association between an increased injury risk and previous injury and increased joint laxity. There is additional evidence to support a relationship between injuries and higher soccer exposure, playing position, increased BMI, low H/Q ratio, player's level of balance and co-ordination, as well as various psychological issues. However, there were conflicting findings for the effect of postural control. Individual differences in Q-angle, intercondylar notch width or pelvic width measurements were not found to be associated with injury. The incidence of injury was higher in the dominant limb. The risk of injury in elite female soccer players is multifactorial, complex, and associated with a range of intrinsic, and extrinsic factors. More high-quality studies are needed to investigate each identified risk factor in order to inform effective injury screening.





Latest research in football - week 3 - 2020

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 The Effect of Respiratory Muscle Training on the Pulmonary Function, Lung Ventilation, and Endurance Performance of Young Soccer Players
Reference: Int J Environ Res Public Health. 2019 Dec 28;17(1). pii: E234. doi: 10.3390/ijerph17010234.
Authors: Mackała K, Kurzaj M, Okrzymowska P, Stodółka J, Coh M, Rożek-Piechura K
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Summary: This study investigated whether the addition of eight weeks of inspiratory muscle training (IMT) to a regular preseason soccer training program, including incremental endurance training (IET), would change pulmonary function, lung ventilation, and aerobic performance in young soccer players. Sixteen club-level competitive junior soccer players (mean age 17.63 ± 0.48 years, height 182 ± 0.05 cm, body mass 68.88 ± 4.48 kg) participated in the study. Participants were randomly assigned into two groups: experimental (n = 8) and control (n = 8). Both groups performed regular preseason soccer training, including endurance workouts as IET. In addition to this training, the experimental group performed additional IMT for eigght weeks with a commercially available respiratory muscle trainer (Threshold IMT), with a total of 80 inhalations (twice per day, five days per week). Pre- and post-intervention tests of pulmonary function, maximal inspiratory pressure, and the Cooper test were implemented. Eight weeks of IMT had a positive impact on expiratory muscle strength (p = 0.001); however, there was no significant effect on respiratory function parameters. The results also indicate increased efficiency of the inspiratory muscles, contributing to an improvement in aerobic endurance, measured by VO₂max estimated from running distance in the cardiorespiratory Cooper test (p < 0.005).

#2 Effects of Nordic Hamstring Exercise on Hamstring Injuries in High School Soccer Players: A Randomized Controlled Trial
Reference: Int J Sports Med. 2020 Jan 5. doi: 10.1055/a-1034-7854. [Epub ahead of print]
Authors: Hasebe Y, Akasaka K, Otsudo T, Tachibana Y, Hall T, Yamamoto M
Summary: We evaluated a range of physical characteristics related to hamstring injuries, as well as the Nordic Hamstring Exercise compliance rate, and whether this influenced the rate hamstring injury. Subjects comprised 259 male soccer players from seven high schools randomly clustered into two groups, a Nordic Hamstring Exercise group and a control group. Training and match time were logged, as well as details of hamstring injury, and subsequent time lost to hamstring injury recorded over a period of 27 weeks. The Nordic Hamstring Exercise compliance rate, injury rate per 10000 playing hours and time-lost-to-sport-injury rate were calculated. The relative risk and hamstring injury severity were also calculated. The hamstring injury rate was 1.04/10 000 h in the control group and 0.88/10 000 h in the intervention group. The relative risk for hamstring injury was 1.14. The time-lost to injury rate was 1116.3/10 000 h in the control group and 113.7/10 000 h in the intervention group; with relative risk 9.81. The Nordic Hamstring Exercise in high school soccer players significantly reduced hamstring injury severity compared to a control intervention. Our results indicate that the time-lost to injury rate should be taken into account when analyzing the severity of hamstring injury.

#3 Taking the First Steps Toward Integrating Testing and Training Cognitive Abilities Within High-Performance Athletes; Insights From a Professional German Football Club
Reference: Front Psychol. 2019 Dec 13;10:2773. doi: 10.3389/fpsyg.2019.02773. eCollection 2019.
Authors: Beavan A, Spielmann J, Mayer J
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#4 Corrigendum: Observational Studies in Male Elite Football: A Systematic Mixed Study Review
Reference: Front Psychol. 2019 Dec 16;10:2682. doi: 10.3389/fpsyg.2019.02682. eCollection 2019.
Authors: Preciado M, Anguera MT, Olarte M, Lapresa D
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#5 Rapid hamstrings to quadriceps ratio at long muscle lengths in professional football players with previous hamstring strain injury
Reference: Eur J Sport Sci. 2020 Jan 9:1-16. doi: 10.1080/17461391.2020.1714741. [Epub ahead of print]
Authors: Correia P, Santos P, Mil-Homens P, Gomes M, Dias A, Valamatos MJ
Summary: Hamstring strain injuries (HSI) are the most common injury in male professional football and are potentially a primary risk factor to re-injury. Although the isokinetic strength ratios have often been used to identify strength imbalances that can augment the risk of injury in football players, the rate of torque development hamstring to quadriceps ratio (RTD H/Q) has rarely been considered in previous reports. Furthermore, little consideration has been given to selective hamstring lengths (30° of knee flexion) and its influence on torque production. The aim of this study was to investigate the RTD H/Q at long hamstring lengths, conventional (concentric/concentric) and functional (eccentric/concentric) H/Q ratios in football players with and without previous HSI. Twenty-four professional male football players (12 with and 12 without previous HSI) performed maximal voluntary isometric contractions at long hamstring lengths (knee and hip flexed at 30° and 85°, respectively) and isokinetic concentric and eccentric contractions at 180°.s-1 and 60°.s-1. Conventional and functional H/Q ratios based on peak torque throughout the entire isokinetic range of motion and at long hamstring lengths were calculated. The RTD H/Q was extracted at long hamstring lengths in incrementing time periods of 50 milliseconds (ms) from the onset of contraction (50-250ms). No significant differences were found between groups in any H/Q ratios studied. However, small effects (d=0.4) were found in previously injured hamstrings to lower RTD H/Q at 50ms and flexor eccentric torque. Previous HSI group showed small to moderate (0.4>d<0.6) higher RTD H/Q in late time intervals (>100ms).

#6 Hill on a mountaintop: A longitudinal and cross-sectional analysis of the relative age effect in competitive youth football
Reference: J Sports Sci. 2020 Jan 9:1-7. doi: 10.1080/02640414.2019.1706830. [Epub ahead of print]
Authors: Jackson RC, Comber G
Summary: The aim of this study was to examine the origin and persistence of the relative age effect (RAE) in competitive youth football. To examine its origin, birthdates of 121 category one Premier League academy players recruited over 6 years were compared with 691 Under 8 (U8) players in one of the regional grassroots leagues from which academy players are selected. To examine the persistence of the RAE we conducted a longitudinal comparison of retention rates in early-birth and late-birth academy players from U9 to U15, and made a cross-sectional comparison of birthdate distributions from U7 to U18 in 10,857 regional league players. The results revealed birthdate asymmetry in both the academy and grassroots players but a much larger RAE in the academy. Longitudinal analysis revealed that the cumulative probability of retention at the academy was higher for early-birth than late-birth players. A small to medium RAE persisted across grassroots football age groups though it declined somewhat from U15 to U18. The implication of these results for academy player recruitment is discussed.

#7 Agility Testing in Youth Football (Soccer)Players; Evaluating Reliability, Validity, and Correlates of Newly Developed Testing Protocols
Reference: Int J Environ Res Public Health. 2020 Jan 1;17(1). pii: E294. doi: 10.3390/ijerph17010294.
Authors: Krolo A, Gilic B, Foretic N, Pojskic H, Hammami R, Spasic M, Uljevic O, Versic S, Sekulic D
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Summary: Reactive agility (RAG) and change of direction speed (CODS) are important determinants of success in football (soccer), but there is an evident lack of information on reliable and valid football-specific testing procedures which will be applicable in defining sport-specific RAG and CODS in youth players. This study evaluated reliability and construct validity of newly developed tests of football-specific RAG (FS_RAG) and CODS (FS_CODS), which involved the ball kicking football technique. Additionally, factors associated with FS_RAG and FS_CODS were evaluated. The participants were youth football players (n = 59; age: 13.40 ± 1.25 years) divided according to their age into U13 (11-12 years of age; n = 29), and U15 (13-14 years of age; n = 30) categories. Additionally, performance levels (starters [first-team] vs. non-starters [substitutes]) were observed in each age category. The dependent variables were newly developed FS_RAG and FS_CODS tests. The independent variables were sprinting capacities over 10 and 20 meters (S10M, S20M), countermovement jump (CMJ), the reactive strength index (RSI), and a generic CODS test of 20 yards (20Y). The newly developed FS_CODS and FS_RAG were observed as dependent variables. Results showed appropriate intra-testing and inter-testing reliability of the FS_RAG and FS_CODS, with somewhat better reliability of the FS_CODS (ICC=0.82 and 0.79, respectively). Additionally, better reliability was evidenced in U15 than in U13 (ICC: 0.82-0.85, and 0.78-0.80 for U15 and U13, respectively). Independent samples t-test indicated significant differences between U13 and U15 in S10 (t-test: 3.57, p < 0.001), S20M (t-test: 3.13, p < 0.001), 20Y (t-test: 4.89, p < 0.001), FS_RAG (t-test: 3.96, p < 0.001), and FS_CODS (t-test: 6.42, p < 0.001), with better performance in U15. Starters outperformed non-starters in most capacities among U13, but only in FS_RAG among U15 (t-test: 1.56, p < 0.05). Multiple regression calculations indicated nonsignificant association between independent and dependent variables in U13 (FS_CODS: 19%, FS_RAG: 21% of the explained variance, both p > 0.05), but independent variables explained significant proportion of both dependent variables in U15 (FS_CODS: 35%, FS_RAG: 33% explained variance, both p < 0.05). The study confirmed the applicability of newly developed tests in distinguishing studied age categories of players. Results indicate that superiority in all studied fitness capacities is translated into performance level in U13. Meanwhile, FS_RAG seems to be important determinant of quality in U15.

#8 BDNF Val66Met Positive Players Demonstrate Diffusion Tensor Imaging Consistent With Impaired Myelination Associated With High Levels of Soccer Heading: Indication of a Potential Gene-Environment Interaction Mechanism
Reference: Front Neurol. 2019 Dec 11;10:1297. doi: 10.3389/fneur.2019.01297. eCollection 2019.
Authors: Hunter LE, Freudenberg-Hua Y, Davies P, Kim M, Fleysher R, Stewart WF, Lipton RB, Lipton ML
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Summary: The purpose of this study was to examine the potential effect modifying role of the BDNF Val66Met polymorphism on the association of soccer heading with white matter microstructure. We studied 312 players enrolled in the ongoing Einstein Soccer Study, a longitudinal study of amateur soccer player in New York City and surrounding areas. At enrollment and 2 years later, total heading in the prior 12 months (12-mo.) was estimated using an established self-report instrument and diffusion tensor imaging (DTI) was performed. Generalized Estimating Equations (GEE) logistic regression models were employed to test effect modification by the BDNF Val66Met polymorphism on the association between 12-mo. heading exposure and DTI. We identified a significant interaction of 12-mo heading*BDNF Val66Met genotype on the presence of low Radial Diffusivity, a DTI marker associated with myelination. Only Met (+) players demonstrated significantly reduced odds of low RD [OR (95 % CI): -2.36 (-3.53, -1.19)] associated with the highest vs. lowest quartile of 12-mo heading exposure. BDNF Val66Met (+) soccer players with long-term exposure to high levels of heading exhibit less low Radial Diffusivity, suggesting impaired re-myelination may be a substrate of the previously reported association between heading and poor functional outcomes in soccer players.

#9 Effect of deep transverse friction massage vs stretching on football players' performance
Reference: World J Orthop. 2020 Jan 18;11(1):47-56. doi: 10.5312/wjo.v11.i1.47. eCollection 2020 Jan 18.
Fakhro MA1, Chahine H2, Srour H2, Hijazi K2.
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Summary: Flexibility, agility and muscle strength are key factors to either win or lose a game. Recently the effect of a new technique, deep transverse friction massage (DTFM) on muscle extensibility as compared to traditional stretching techniques has been examined. The aim was to compare the effect of DTFM vs static and dynamic stretching techniques on the hamstring's extensibility, agility, and strength amongst Lebanese and Syrian football players. Recording the incidence of non-contact hamstring muscle injury was a secondary objective. This study is a single-blinded prospective longitudinal randomized controlled trial. The experiment took place over a period of four weeks. Football players were randomized into three intervention groups (static stretching; dynamic stretching; DTFM). Participants of each group were followed-up carefully by assessors during their intervention sessions three times per week, for a total of 12 sessions and during the data collection. Extensibility, agility, and strength were compared between intervention groups at (baseline; acute; and chronic) phases. Straight leg raise and 1 repetition maximum tests were used to measure the dominant leg hamstring muscle extensibility and maximal strength respectively. T-drill test was used to assess the lower extremities agility. Of 103 Lebanese and Syrian male football players aged between 18 and 35 were sampled from Damascus-Syria and South of Lebanon to participate in this study. Between-groups measures of acute strength (P = 0.011) and chronic extensibility (P = 0.000) solely showed a significant difference, and the static group showed to be superior as compared to the other groups. No loss to follow-up or protocol violation was recorded. Static stretching is showing to be superior to the other techniques used, regarding gaining long-term extensibility and short-term maximal muscle strength. In addition, DTFM showed improvements but did not outweigh the effects on footballers' performance when comparing it to static and dynamic techniques. Finally, no difference between the interventions is recorded regarding the rate of muscle injuries incidence.

#10 Evaluation of the Technical Performance of Football Players in the UEFA Champions League
Reference: Int J Environ Res Public Health. 2020 Jan 17;17(2). pii: E604. doi: 10.3390/ijerph17020604.
Authors: Yi Q, Gómez-Ruano MÁ, Liu H, Zhang S, Gao B, Wunderlich F, Memmert D
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Summary: This study aimed to assess the technical match performance of top-class football players in a long-term perspective. Technical performance profiles of players according to five playing positions (central defender, full back, wide midfielder, central midfielder, forward) and five situational variables (competition stage, match location, quality of team, quality of opponent, match outcome) were established. Technical match data of players in the UEFA Champions League from season 2009-2010 to 2016-2017 were analyzed. The true effects of positional and situational variables on players' technical performance were evaluated by the non-clinical magnitude-based inference. Results showed that the effect of competition stage on player's performance was negligible. Quality of team, quality of opponent and match outcome revealed the strongest effects on player's performance (ES: -0.42 ± 0.10-0.59 ± 0.10) while the effect of match location was relatively lower (ES: -0.32 ± 0.10-0.23 ± 0.07). The number of variables that showed statistical differences under five competing contexts for wide midfielders and forwards were higher than those of central defenders, full backs, and central midfielders. Differences of players' match performance could mainly be identified in variables related to goal scoring, passing, and organizing, these findings may provide important insights for coaches and analysts during the match preparation and training session.

#11 Scale-Up and Scale-Out of a Gender-Sensitized Weight Management and Healthy Living Program Delivered to Overweight Men via Professional Sports Clubs: The Wider Implementation of Football Fans in Training (FFIT)
Reference: Int J Environ Res Public Health. 2020 Jan 16;17(2). pii: E584. doi: 10.3390/ijerph17020584.
Authors: Hunt K, Wyke S, Bunn C, Donnachie C, Reid N, Gray CM
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Summary: Increasing prevalence of obesity poses challenges for public health. Men have been under-served by weight management programs, highlighting a need for gender-sensitized programs that can be embedded into routine practice or adapted for new settings/populations, to accelerate the process of implementing programs that are successful and cost-effective under research conditions. To address gaps in examples of how to bridge the research to practice gap, we describe the scale-up and scale-out of Football Fans in Training (FFIT), a weight management and healthy living program in relation to two implementation frameworks. The paper presents: the development, evaluation and scale-up of FFIT, mapped onto the PRACTIS guide; outcomes in scale-up deliveries; and the scale-out of FFIT through programs delivered in other contexts (other countries, professional sports, target groups, public health focus). FFIT has been scaled-up through a single-license franchise model in over 40 UK professional football clubs to 2019 (and 30 more from 2020) and scaled-out into football and other sporting contexts in Australia, Canada, New Zealand, England and other European countries. The successful scale-up and scale-out of FFIT demonstrates that, with attention to cultural constructions of masculinity, public health interventions can appeal to men and support them in sustainable lifestyle change.





Latest research in football - week 2 - 2020

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Groin Injuries in Soccer: Investigating the Effect of Age on Adductor Muscle Forces
Reference: Med Sci Sports Exerc. 2019 Dec 31. doi: 10.1249/MSS.0000000000002243. [Epub ahead of print]
Authors: Dupré T, Lysdal FG, Funken J, Mortensen KRL, Müller R, Mayer J, Krahl H, Potthast W
Summary: The sudden rise in the injury incidence during adolescence, is also evident in soccer related injuries to the groin. Submaximal passing applies high stress on the adductor muscles and pubic symphysis and is therefore likely to be connected to the occurrence of groin injuries. Therefore, the purpose of the study was to compare hip joint kinematics and adductor muscle forces of different adolescent age groups during submaximal soccer passing. Sixty participants, in four groups, below 12, 15, 16 and 23 years (U12, U15, U16, U23), were analyzed. A Footbonaut, equipped with a 3D motion capture system consisting of 16 cameras, was used to capture kinematic data of short passes. Inverse dynamic analysis was performed to calculate muscle forces of ten passes of each subject. The U15 group showed reduced angular velocities. A rise in hip adductor muscle forces was evident from the youngest group up to the oldest groups. The largest increase (49%) was found between U12 and U15. Lower limb mass was identified as the best predictor for the increasing adductor force. The reduced angular velocities of the U15 and the increase in muscle forces between all age groups was attributed to the increasing segment masses and length. This increases the moments of inertia of the leg segments thereby demanding higher forces to accelerate the segments. Most likely, the stress put upon the adductors apophyses increases during adolescence, as tendons are known to adapt slower than muscles, increasing the risk for overuse injuries. Coaches could use lower limb mass as an indicator for fast increases in the force demand to identify players who would benefit from a reduced training volume.

#2 Pathoanatomy of the Jones Fracture in Male University Soccer Players
Reference: Am J Sports Med. 2019 Dec 30:363546519893365. doi: 10.1177/0363546519893365. [Epub ahead of print]
Authors: Fujitaka K, Tanaka Y, Taniguchi A, Ogawa M, Isomoto S, Otuki S, Okubo M
Summary: Jones fractures are relatively common in soccer players and require an extended recovery period because this type of fracture has a high incidence of delayed union, nonunion, and refracture. There has been some previous research on risk factors for Jones fracture, but no study has yet investigated the effect of the length of the fifth metatarsal bone and the positional relationship of the articular surface of the fifth metatarsal bones and the tarsal bones. Clarification of the characteristics of the foot structure that predispose soccer players to Jones fracture may aid in the prevention of this injury. The purpose was to investigate the association between Jones fracture and foot structure as assessed with a mapping system on weightbearing dorsoplantar and lateral foot radiographs. We used a mapping system to evaluate the radiographs of 60 feet from 30 university soccer players with Jones fractures and a control group of 60 feet from 60 male university soccer players without Jones fracture. The groups were compared regarding the length of the fifth metatarsal and the positions of the metatarsal and tarsal bones. Analysis of weightbearing dorsoplantar foot radiographs showed that the fifth metatarsal was significantly longer and that its proximal tip was positioned more proximally in the Jones fracture group as compared with the control group. Analysis of weightbearing lateral foot radiographs showed that the reference points for the medial arch were significantly higher in the Jones fracture group than in the control group. This study indicated that the proximally longer fifth metatarsal may cause greater stress at the base of the fifth metatarsal bone because the lever arm becomes long. In addition, high medial longitudinal arch may contribute to increased load on the lateral side of the foot. Thus, these anatomic features may be useful to identify soccer players at high risk of Jones fracture at medical checkup.

#3 Multidirectional Plyometric Training: Very Efficient Way to Improve Vertical Jump Performance, Change of Direction Performance and Dynamic Postural Control in Young Soccer Players
Reference: Front Physiol. 2019 Dec 9;10:1462. doi: 10.3389/fphys.2019.01462. eCollection 2019.
Authors: Jlid MC, Racil G, Coquart J, Paillard T, Bisciotti GN, Chamari K
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Summary: The aim of the study was to assess the effects of multidirectional plyometric training (MPT) on vertical jump height, change of direction performance (CODP), and dynamic postural control (DPC) in young soccer players. Twenty-eight young male soccer players were randomly assigned to an experimental group (EG, n = 14; age: 11.8 ± 0.4 years) and a control group (CG, n = 14; age: 11.6 ± 0.5 years). The EG introduced 8-week MPT, two days per week into their in-season training, while CG continued training without change. Measurements of vertical jump height, CODP, and DPC were completed at the beginning and end of the 8-week MPT. A significant group × time interaction was observed for Squat-Jump (p < 0.05), for Counter-Movement Jump (p < 0.05), and for CODP test (p < 0.05). In addition, a significant group × time interaction was observed for DPC in seven axes for the dominant- (anterior, lateral, postero-lateral, posterior, postero-medial, medial, and antero-medial; p < 0.05 for all) and in seven axes for the non-dominant- (anterior, antero-lateral, lateral, posterior, postero-medial, medial and antero-medial; p < 0.05 for all) legs. The rest of the axes of both legs did not show any significant group × time interaction (p > 0.05). In conclusion, incorporating MPT into the in-season regimen of young male soccer players improved performance of various indices related to soccer activity (i.e., vertical jump height, CODP, and DPC). MPT has the potential to be appealing to coaches, as it requires little time while yielding valuable results in the physical preparation of young soccer players.

#4 Predictive modelling of the physical demands during training and competition in professional soccer players
Reference: J Sci Med Sport. 2019 Dec 17. pii: S1440-2440(19)31238-1. doi: 10.1016/j.jsams.2019.12.008. [Epub ahead of print]
Authors: Giménez JV, Jiménez-Linares L, Leicht AS, Gómez MA
Summary: The present study aimed to predict the cut-off point-values that best differentiate the physical demands of training and competition tasks including friendly matches (FM), small sided games (SSG), large sided games (LSG), mini-goal games (MG) and ball circuit-training (CT) in professional soccer players. Fourteen professional players participated in all tasks with the CT, SSG and MG consisting of 8 repetitions of 4-min game play, interspersed by 2-min of active recovery. The training data were compared to the first 32-min of the LSG and two competitive FM per player. All movement patterns from walking to sprint running were recorded using 10Hz GPS devices while player perception of exertion was recorded via a visual analogue scale, post-task. Decision tree induction was applied to the dataset to assess the cut-off point-values from four training drills (SSG, LSG, MG, and CT) and FM for every parameter combination. Distance covered during jogging (2.3-3.3m/s; >436m), number of decelerations (≤730.5) and accelerations (≤663), and maximum velocity reached (>5.48m/s) characterized the physical demands during competition (FM) with great variability amongst training drills. The use of these novel, cut-off points may aid coaches in the design and use of training drills to accurately prepare athletes for soccer competition.

#5 Technical-Tactical Analysis of the Players of the Left and Right Wing in Elite Soccer
Reference: J Hum Kinet. 2019 Nov 30;70:233-244. doi: 10.2478/hukin-2019-0045. eCollection 2019 Nov.
Authors: Amatria M, Dios RM, Pérez-Turpin JA, Gomis-Gomis MJ, Elvira-Aranda C, Suárez-Llorca C
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Summary: In today's soccer, teams are increasingly better trained both physically and tactically, hence different game styles can be identified and differences between them reduced. However, without an exhaustive analysis of reality, the view can lead to the extraction of erroneous conclusions, and what seems to be a team with a marked offensive profile is a mere illusion, resulting to be a team that develops a perfectly balanced game. In this paper, an analysis of technical-tactical performance of players who occupied both wings in an elite team was made, taking as reference the Spanish national soccer team as the model of international game to imitate in the last decade. The development of this paper was located within the observational methodology, using the polar coordinates technique for the analysis of the obtained data. The results showed how, despite identifying offensive profiles within technical-tactical performance of players that occupied the outer wings or lanes of the playing field, their tactical means and orientations diverged from each other. The results showed a more offensive profile and with higher technical complexity of players that occupied the left wing, while players that held the right wing showed a more defensive and recuperative profile, indicating a less vertical and complex style of play at a technical level with the forward as an offensive reference.

#6 External Load Variations Between Medium- and Large-Sided Soccer Games: Ball Possession Games Vs Regular Games with Small Goals
Reference: J Hum Kinet. 2019 Nov 30;70:191-198. doi: 10.2478/hukin-2019-0031. eCollection 2019 Nov.
Authors: Clemente FM, Praça GM, Bredt SDGT, van der Linden CMI, Serra-Olivares J
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Summary: This study compared external load variations between 5 vs 5 and 10 vs 10 sided game formats played under two conditions: (i) a ball possession game with two floaters, and (ii) a regular game with goalkeepers and small goals. Twenty-two professional soccer players participated in this study: four central defenders, four wide defenders, nine central midfielders, three wide forwards, and three strikers. Total distance (TD), running distance (RD), sprinting distance (SD), number of sprints (NS), and player's training load (PL) were recorded by GPS units. Within-format analyses revealed very likely large increases in TD (20.0%, [9.2; 31.9]; effect size (ES): 1.48, [0.71; 2.25]) and RD (130.9%, [20.2; 343.7]; ES: 1.32, [0.29; 2.35]) during the regular game when compared to the ball possession game in the 5 vs 5 format. In the 10 vs 10 format, large increases in TD (27.9%, [17.7; 39.1]; ES: 3.54, [2.34; 4.74]) and PL (27.4%, [12.6; 44.1]; ES: 2.46, [1.20; 3.72]) were observed in the regular condition when compared to the ball possession condition. Between-formats analyses revealed that, in the 10 vs 10 format, when compared to the 5 vs 5 format, RD was very likely larger (123.5%, [33.7; 273.7]), as was SD (195.8%, [20.5; 626.2]). However, very likely large decreases in PL were observed in the 10 vs 10 format (-19.6%; [-29.4; -8.3]) in the ball possession condition. Unclear differences were revealed based on variations in external load variables between formats in the regular condition. Smaller formats reduce the area available for running and sprinting and, thus, may be more adequate for increasing player's training load (based on accelerometer data).

#7 Short-Term Repeated-Sprint Training (Straight Sprint Vs. Changes of Direction) in Soccer Players
Reference: J Hum Kinet. 2019 Nov 30;70:183-190. doi: 10.2478/hukin-2019-0040. eCollection 2019 Nov.
Authors: Beato M, Coratella G, Bianchi M, Costa E, Merlini M
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Summary: Repeated-sprint training (RST) is considered a critical training method in team sports. It is well known that RST effects may depend on several variables such as the duration of the protocol and repeated-sprint methodology. Few studies have evaluated very short-term protocols and compared different RST modalities. The aim of this study was to compare the effectiveness of 2 week RST including straight sprints or changes of direction (CODs) on physical performance in a sample of soccer players. This study used a randomised pre-post parallel group trial design. The participants were assigned to either an RST group using straight sprints (RST-SS = 18 players) or an RST group using CODs (RST-COD = 18 players). The protocols were: 3 sets of 7 x 30 m sprints for the RST-SS and 7 x 20 + 20 m (one COD of 180°) for the RST-COD, with 20 s and 4 min recovery between sprints and sets, respectively. The following evaluations were performed: 10 and 20 m sprint, agility test, repeated sprint test (RSTbest and RSTmean), and Yo-Yo Recovery Level 1. After the training period, the RST-SS did not report any performance variation, while the RST-COD showed improvements in the 10 m sprint and RSTbest (effect size = 0.70 and 0.65, respectively). The between-group analysis did not report any statistical difference between the RST-SS and the RST-COD. In conclusion, this study did not support the utilisation of a very short-term RST protocol with soccer players, however, the RST-COD presented some additional benefits in sprint performance compared to the RST-SS.

#8 Analysis of Match Dynamics of Different Soccer Competition Levels Based on the Player Dyads
Reference: J Hum Kinet. 2019 Nov 30;70:173-182. doi: 10.2478/hukin-2019-0030. eCollection 2019 Nov.
Authors: Caetano FG, da Silva VP, Torres RDS, Anido RO, Cunha SA, Moura FA
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Summary: The purpose of this study was to analyse the dynamics of play based on dyads during soccer matches, according to the competition level, period of the matches, and playing positions. We recorded eight Brazilian soccer matches (four of the national and four of the regional level), using up to six digital cameras (30 Hz). The position information of the 204 players in the eight matches was obtained using an automatic tracking system. The Euclidean distance between the nearest opponents was calculated over time to define the dyads. The interaction between the components of dyads was assessed by the distances between players and was compared among the different positions (defender, full-back, defensive midfielder, midfielder, and forward), match periods (15, 30, 45, 60, 75, and 90 min), and competition levels. Results showed smaller distances for the national level dyads, compared to the regional matches. Greater distances between the players were found in the last 15 minutes of the matches, compared to the other periods. The full-backs were more distant from opposing players compared to players from other playing positions. Thus, coaches should consider the characteristics of each playing position and the greater proximity between opponents' players in top-level competition for the development of tactical proficiency of the players.

#9 Different Cleat Models Do Not Influence Side Hop Test Performance of Soccer Players with and Without Chronic Ankle Instability
Reference: J Hum Kinet. 2019 Nov 30;70:156-164. doi: 10.2478/hukin-2019-0029. eCollection 2019 Nov.
Authors: Silva DCF, Santos R, Vilas-Boas JP, Macedo R, Montes AM, Sousa ASP
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Summary: The lateral ankle sprain is one of the most common sport injury, representing 10-30% of all musculoskeletal disorders. The lateral ankle sprain is induced by sport gestures involving changes of direction and landing manoeuvres and constitutes a risk factor for the occurrence of chronic ankle instability. Although cleat models and performance have been already explored, no study has evaluated this relationship in athletes with chronic ankle instability. Therefore, the purpose of the study was to analyse the influence of different soccer cleat models on Side Hop Test performance of athletes with and without chronic ankle instability. Thirty-nine athletes were divided into two groups, a chronic ankle instability group (n = 20) and a healthy group (n = 19). Each participant performed the Side Hop Test, executing 10 consecutive jumps on dry artificial grass with 4 cleat models. The Qualisys System and two force platforms were used to analyse the test runtime, the distance travelled and the mean velocity. No statistically significant interaction was observed between the group and the cleat model for all variables evaluated. In addition, no differences were observed between models or groups. In this specific test, performance does not seem to be influenced by different cleat models on dry artificial grass in athletes with and without chronic ankle instability.

#10 Assessment of Lower Body and Abdominal Strength in Professional Soccer Players
Reference: J Hum Kinet. 2019 Nov 30;70:15-23. doi: 10.2478/hukin-2019-0035. eCollection 2019 Nov.
Authors: Michaelides MA, Parpa KM, Zacharia AI
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Summary: The purpose of this study was to evaluate abdominal strength in professional soccer players and compare the findings to their lower body strength. An observational design was used to examine abdominal and lower body strength using two functional performance tests (a lower body isokinetic test and an isometric abdominal test, respectively). One hundred and thirty-two professional male soccer players from Cyprus's first and second divisions participated in this study. Testing included three and twenty-five maximal concentric flexion and extension repetitions at angle speeds of 60°/s (degrees/second) and 300°/s, respectively. On a separate occasion, participants completed two trials on an isometric device (ABTEST Gen. 3 system) for evaluation of abdominal strength. At both isokinetic speeds of 300°/s and 60°/s, abdominal strength had low to moderate significant correlations (p < .05) with quadriceps and hamstring strength. Coefficients of determination (R2) demonstrated that the variability in isokinetic variables accounted for only 14-16% of the variability of abdominal strength. Abdominal strength appears to be high in professional soccer players, but is not dependent on the sports level and/or a playing position. The results of this study demonstrate that abdominal strength and knee joint strength need to be evaluated separately.

#11 Effects of fatigue induced by repeated-sprint on kicking accuracy and velocity in female soccer players
Reference: PLoS One. 2020 Jan 7;15(1):e0227214. doi: 10.1371/journal.pone.0227214. eCollection 2020.
Authors: Torreblanca-Martínez V, Nevado-Garrosa F, Otero-Saborido FM, Gonzalez-Jurado JA
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Summary: The aim of this study was to investigate the effects of fatigue induced by repeated sprint in the kicking accuracy and velocity in female soccer players. Eighteen Under-23 female soccer players from a Spanish professional club were subjected to a fatigue protocol based on a repeated-sprint ability (RSA) test. Measurements of the kicking velocity (maximal ball velocity) and accuracy (Loughborough Soccer Shooting Test) were taken before and after fatigue induction. Correlations between the change in the maximal ball velocity/accuracy and the heart rate (HR), the fatigue index (FI), the sprint decrement (Sdec) and the rating of perceived exertion (RPE) were made. There was a significant difference between maximal ball velocity under fatigue conditions with respect to non-fatigue conditions (p = 0.001; ES = 0.89). However, despite a lower kicking accuracy punctuation with fatigue, this was not statistically significant (p = 0.433; ES = 0.22). Significant correlations were found between the maximal kicking velocity and the FI (r = 0.632, p < 0.01) and the Sdec (r = -0.554, p < 0.05) and between the kicking accuracy and the RPE (r = -0.506, p < 0.05). In conclusion, there was a significant reduction in the maximal kicking velocity, but not in the kicking accuracy, under fatigued conditions. The RSA-related FI and Sdec were the best predictors of the maximal kicking velocity and the RPE for the kicking accuracy.

#12 Agility Testing in Youth Football (Soccer)Players; Evaluating Reliability, Validity, and Correlates of Newly Developed Testing Protocols
Reference: Int J Environ Res Public Health. 2020 Jan 1;17(1). pii: E294. doi: 10.3390/ijerph17010294.
Authors: Krolo A, Gilic B, Foretic N, Pojskic H, Hammami R, Spasic M, Uljevic O, Versic S, Sekulic D
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Summary: Reactive agility (RAG) and change of direction speed (CODS) are important determinants of success in football (soccer), but there is an evident lack of information on reliable and valid football-specific testing procedures which will be applicable in defining sport-specific RAG and CODS in youth players. This study evaluated reliability and construct validity of newly developed tests of football-specific RAG (FS_RAG) and CODS (FS_CODS), which involved the ball kicking football technique. Additionally, factors associated with FS_RAG and FS_CODS were evaluated. The participants were youth football players (n = 59; age: 13.40 ± 1.25 years) divided according to their age into U13 (11-12 years of age; n = 29), and U15 (13-14 years of age; n = 30) categories. Additionally, performance levels (starters [first-team] vs. non-starters [substitutes]) were observed in each age category. The dependent variables were newly developed FS_RAG and FS_CODS tests. The independent variables were sprinting capacities over 10 and 20 meters (S10M, S20M), countermovement jump (CMJ), the reactive strength index (RSI), and a generic CODS test of 20 yards (20Y). The newly developed FS_CODS and FS_RAG were observed as dependent variables. Results showed appropriate intra-testing and inter-testing reliability of the FS_RAG and FS_CODS, with somewhat better reliability of the FS_CODS (ICC=0.82 and 0.79, respectively). Additionally, better reliability was evidenced in U15 than in U13 (ICC: 0.82-0.85, and 0.78-0.80 for U15 and U13, respectively). Independent samples t-test indicated significant differences between U13 and U15 in S10 (t-test: 3.57, p < 0.001), S20M (t-test: 3.13, p < 0.001), 20Y (t-test: 4.89, p < 0.001), FS_RAG (t-test: 3.96, p < 0.001), and FS_CODS (t-test: 6.42, p < 0.001), with better performance in U15. Starters outperformed non-starters in most capacities among U13, but only in FS_RAG among U15 (t-test: 1.56, p < 0.05). Multiple regression calculations indicated nonsignificant association between independent and dependent variables in U13 (FS_CODS: 19%, FS_RAG: 21% of the explained variance, both p > 0.05), but independent variables explained significant proportion of both dependent variables in U15 (FS_CODS: 35%, FS_RAG: 33% explained variance, both p < 0.05). The study confirmed the applicability of newly developed tests in distinguishing studied age categories of players. Results indicate that superiority in all studied fitness capacities is translated into performance level in U13. Meanwhile, FS_RAG seems to be important determinant of quality in U15.





Latest research in football - week 1 - 2020

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Evaluation of soccer players under the Moneyball concept
Reference: J Sports Sci. 2019 Dec 26:1-27. doi: 10.1080/02640414.2019.1702280. [Epub ahead of print]
Authors: Gavião LO, Sant'Anna AP, Alves Lima GB, de Almada Garcia PA
Summary: The recruitment of athletes with limited resources is a global problem in professional sports. In US Major League Baseball, the experience of the Oakland Athletics' general manager in the last decade turned his "Moneyball" model into a synonym of quantitative analysis in the transfer market of baseball players. His strategy focused on hiring players with outstanding technical skills but relatively low market value. This study adapted this model to the framework of a multiple criteria decision aid (MCDA), by selecting undervalued players who have complementary abilities. The novelty here refers to the joint use of four algorithms explored by the composition of probabilistic preferences (CPP) (i.e., ranking, classification, dynamic evaluation and regularity analysis) and their application to soccer player performance evaluation. The new model analysed the recent transfer of a left-back soccer player to Europe. The results indicated 12 opportunities for better investment, among 32 left and right-back players considered. Two years later, the value of the same player was considerably lower. He played only five matches in the 2018-2019 season, without scoring or providing any assists. On the other hand, the players better classified by the CPP-MB model presented higher performances and market values.

#2 Treatment of Anterior Cruciate Ligament Injuries in Professional Soccer Players by Orthopedic Surgeons
Reference: Rev Bras Ortop (Sao Paulo). 2019 Dec;54(6):703-708. doi: 10.1055/s-0039-1697017. Epub 2019 Dec 13.
Authors: Arliani GG, Pereira VL, Leão RG, Lara PS, Ejnisman B, Cohen M
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Summary: The purpose was to describe the treatment provided by specialists for ACL lesions in professional soccer players. A cross-sectional study in which orthopedic surgeons affiliated to soccer teams competing in the Brazilian Soccer Championship answered a questionnaire about the treatment of ACL injuries in professional soccer players. The specialists wait between one to four weeks after the ACL injury to perform the surgical treatment. They use a single incision and single-bundle reconstruction, assisted by arthroscopy, femoral tunnel drilling by an accessory medial portal, and quadruple flexor tendon autografts or patellar tendon autografts. After three to four months, the players are allowed to run in a straight line; after four to six months, they begin to practice exercises with the ball without contact with other athletes; and, after six to eight months, they return to play. The main parameter used to determine the return to play is the isokinetic strength test. The specialists estimate that more than 90% of elite soccer players return to playing professionally after an ACL reconstruction, and 60 to 90% return to play at their prior or at a greater level of performance. The present article successfully describes the main surgical practices and post-surgery management adopted by specialists in this highly-specific population of patients.

#3 Improvements in Match-Related Physical Performance of Professional Soccer Players After the Application of an on-Field Training Program for Hamstring Injury Rehabilitation
Reference: J Sport Rehabil. 2019 Dec 22:1. doi: 10.1123/jsr.2019-0033. [Epub ahead of print]
Authors: Jiménez-Rubio S, Navandar A, Rivilla-García J, Paredes-Hernández V, Gómez-Ruano MÁ.
Summary: Although there are multiple, validated return-to-play programs following hamstring strain injuries, no studies have evaluated their changes in match performance parameters. The aim of this study was twofold as follows: (1) to determine the changes in match-based physical performance parameters in professional soccer players before and after sustaining a hamstring strain injury and undergoing a soccer-specific rehabilitation program and (2) to observe the progress of these performance parameters 6 to 10 weeks after the player returned from injury. Nineteen players suffering a hamstring strain injury from 2 male professional teams playing in the Spanish professional football league (La Liga) were followed during the 2015-2016, 2016-2017, and 2017-2018 seasons. The intervention was a participation in on-field training program following a hamstring injury. Match global positioning system data were collected in the following stages: prior to injury (PRE), after return to play (RTP), program, and 6 to 10 weeks following RTP (C2). Peak velocities and distances ran at sprint velocities showed most likely improvements in C2 versus PRE, and very likely improvements in RTP versus PRE. The distances ran at high and very high intensities, the average velocity, and work-to-rest ratio showed very likely improvements in C2 versus RTP and likely improvements in RTP versus PRE. Likely improvements were observed for all variables in C2 versus RTP. The authors' results showed an improvement of physical performance during competitive match after RTP, compared with PRE. There was a steady progression in the progress, and in 8 months following RTP, there was no injury reported in the players. The current findings may indicate that the hamstring muscle complex not only recovered completely from the injury but could also withstand a greater training and match load reducing the risk of reinjury.

#4 Seasonal variation in neuromuscular control in young male soccer players
Reference: Phys Ther Sport. 2019 Dec 16;42:33-39. doi: 10.1016/j.ptsp.2019.12.006. [Epub ahead of print]
Authors: Lloyd RS, Oliver JL, Myer GD, De Ste Croix M, Read PJ
Summary: Determine how lower limb neuromuscular control changes over the course of a competitive soccer season. 43 male youth soccer players (age 13.1 ± 2.2 yr; height 160.1 ± 15.7 cm; body mass 49.4 ± 14.3 kg; maturity offset 0.2 ± 1.9 yr) participated in this study.  Pre-, mid- and end of season assessments of peak landing forces during single leg 75% horizontal hop and stick (75%HOP) and a single leg countermovement jump (SLCMJ), single leg hop for distance (SLHD), knee valgus during the tuck jump assessment (TJA) and inter-limb symmetries. Hop distance increased significantly. Absolute peak landing forces in the left leg during the SLCMJ and 75%HOP increased significantly, with significant increases also present in the same leg for SLCMJ relative peak landing force. TJA knee valgus score was reduced in the right leg, but remained at a 'moderate' level in the left knee. Neuromuscular control, as evidenced by increased absolute and relative peak landing forces, appears to reduce over the course of a competitive season. Young soccer players should engage in neuromuscular training throughout the season to offset any decrements in neuromuscular control and to facilitate appropriate landing strategies.

#5 Normalized Hip and Knee Strength in Two Age Groups of Adolescent Female Soccer Players
Reference: J Strength Cond Res. 2019 Dec 20. doi: 10.1519/JSC.0000000000003420. [Epub ahead of print]
Authors: Hannon JP, Wang-Price S, Garrison JC, Goto S, Bothwell JM, Bush CA
Summary: Limb symmetry strength measures are used for clinical decision-making considering when an athlete is ready to return to sport after anterior cruciate ligament (ACL) injuries. However, changes in bilateral muscle strength occur after ACL injury resulting in potentially altered limb symmetry calculations. Adolescent female soccer players are at increased risk of sustaining ACL injuries. Published age and sex-matched strength values in this population may be of benefit to clinicians to improve clinical decision-making. The purpose of this study was to establish normative hip and knee strength data of both the dominant and nondominant limbs in adolescent female soccer players. Sixty-four female soccer players (ages 10-18) were enrolled in this study. Subjects were divided by age into 2 groups (group 1: 10-14 years; group 2: 15-18 years). Subjects underwent Biodex isokinetic strength testing at 60°·s and 180°·s to assess quadriceps and hamstring strength. Isometric hip strength (abduction and external rotation) was measured using a hand-held dynamometer. No significant differences were found between groups on either limb in regards to quadriceps or hamstring strength. No significant differences were found between groups on either limb for hip external rotation strength. Significant differences in hip abduction strength were found between groups on the dominant (group 1: 0.21 ± 0.04; group 2: 0.18 ± 0.04; p = 0.014) and nondominant (group 1: 0.21 ± 0.05; group 2: 0.18 ± 0.05; p = 0.019) limbs. The results of this study shed light on normative strength values for a high-risk injury population.

#6 Effects of Ramadan Fasting on Recovery Following a Simulated Soccer Match in Professional Soccer Players: A Pilot Study
Reference: Front Physiol. 2019 Dec 6;10:1480. doi: 10.3389/fphys.2019.01480. eCollection 2019.
Authors: Bouzid MA, Abaïdia AE, Bouchiba M, Ghattassi K, Daab W, Engel FA, Chtourou H
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Summary: Assessing the effects of Ramadan fasting on recovery following a soccer match simulation. Eight elite soccer players (age: 21.0 ± 0.4 years) performed a modified Loughborough Intermittent Shuttle Test protocol (LISTmod) on two occasions: 1 week before (BR) and during the fourth week of Ramadan (End-R). At BR and End-R, soccer players performed squat jump, countermovement jump, maximal voluntary contraction, and 20 m sprint, and creatine kinase, uric acid, and subjective ratings (feelings scale, quality of sleep, fatigue, muscle soreness and stress) were assessed at baseline and 0, 24, 48, and 72 h following LISTmod. Following LISTmod, performance in squat jump (48 and 72 h) (p < 0.05), countermovement jump (48 and 72 h), maximal voluntary contraction (0, 24, 48, and 72 h), and 20 m sprint (0 and 48 h) decreased significantly on both occasions. Decreases were higher at End-R than BR. Creatine kinase levels increased significantly at 24 and 48 h at BR and End-R (p < 0.05). Uric acid increased at 0 and 24 h only on BR. Muscle soreness increased throughout the recovery period at both occasions, with a higher level at End-R. Stress rating increased only at 0 h on End-R, while fatigue rating increased at 24 h at BR and at 0, 24, and 48 h at End-R. Perturbations in physical performance and subjective ratings parameters were higher at the end of Ramadan. However, the results of this study showed that Ramadan fasting did not adversely affect the recovery following soccer match simulation in professional soccer players.

#7 Return to Play in Amateur Soccer Players Undergoing Hip Arthroscopy: Short- to Mid-Term Follow-Up
Reference: Arthroscopy. 2019 Dec 19. pii: S0749-8063(19)30727-3. doi: 10.1016/j.arthro.2019.08.027. [Epub ahead of print]
Authors: Ortiz-Declet V, Yuen LC, Schwarzman GR, Chen AW, Perets I, Domb BG
Summary: The purpose was to describe patient-reported outcomes (PROs) and return to play at any level in amateur soccer players undergoing hip arthroscopy for femoroacetabular impingement syndrome at short- to mid-term follow-up. Data were prospectively collected and retrospectively reviewed for patients who underwent hip arthroscopy between March 2009 and June 2014. Patients who participated in amateur soccer within 1 year prior to surgery and intended to return to their sport after hip arthroscopy for femoroacetabular impingement syndrome were considered for inclusion in our study. Patients were excluded if they had a preoperative Tönnis osteoarthritis grade of 2 or greater, previous ipsilateral hip conditions or hip surgical procedures, or Workers' Compensation status. The patients from the initial group who had preoperative and minimum 2-year postoperative measures for the modified Harris Hip Score, Non-Arthritic Hip Score, Hip Outcome Score-Sports Specific Subscale, and visual analog scale for pain were included in our final group. In addition to PROs, data regarding the patients' return to soccer, surgical complications, and secondary surgical procedures were collected. A total of 41 patients were eligible for inclusion in our study, of whom 34 (82.9%) had a mean follow-up period of 47.4 months. Five patients were not eligible because they did not intend to return to soccer. There were 15 male hips (44.1%) and 19 female hips (55.9%). The mean age at surgery was 20.8 ± 7.4 years. All PROs and the visual analog scale score improved significantly from preoperatively to latest follow-up. Of the 34 patients, 27 (79.4%) returned to soccer. Of the patients who returned to soccer, 19 (70.4%) were competing at the same level or a higher level compared with their highest level within 1 year of surgery. Regardless of competitive level, 21 patients (77.8%) reported that their athletic ability was the same as or higher than it was within 1 year of surgery. Hip arthroscopy was associated with significant improvements in PROs for amateur soccer players. There was a high level of return to soccer and a high proportion of patients whose competitive level was similar or improved. As such, hip arthroscopy is a good option for soccer players, in the absence of underlying osteoarthritis, presenting with hip pathology.

#8 Editorial Commentary: Anterior Cruciate Ligament Injury and Reconstruction in Soccer Players: The Major Challenge Is Always Going for Our Goals!
Reference: Arthroscopy. 2020 Jan;36(1):196-198. doi: 10.1016/j.arthro.2019.10.005.
Authors: Stein SM, Mandelbaum BR
Summary: Anterior cruciate ligament (ACL) injury affects a large number of athletes worldwide, and long-term rate of return to soccer is approximately 50% or less. ACL injury, which is noncontact in approximately 90% of cases, has a complex multifactorial etiology. Younger and higher-level players do better, and 10-year outcomes are superior to baseline. The role of genomics, hormonal status, neuromuscular deficiencies, anatomy, and the environment are all potential contributory risk factors that vary with respect to the individual, especially the female athlete. Furthermore, ACL injury results in a local and regional catabolic cascade and cytokine release, creating an intra-articular environment that is a homeostatic perfect storm and spectrum of scalable articular cartilage and meniscal injury. Once these complexities in the knee organ are defined and understood, the surgeon's early objectives are stabilization, repair, and restoration with full harmonization of biomechanics, neuromuscular control, and homeostasis. The goal is optimizing long-term outcomes, decreasing the rate of subsequent ACL injury, and preventing osteoarthritis.

#9 Positional Differences in Peak- and Accumulated- Training Load Relative to Match Load in Elite Football
Reference: Sports (Basel). 2019 Dec 23;8(1). pii: E1. doi: 10.3390/sports8010001.
Authors: Baptista I, Johansen D, Figueiredo P, Rebelo A, Pettersen SA
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Summary: Quantification of training and match load is an important method to personalize the training stimulus' prescription to players according to their match demands. The present study used time-motion analysis and triaxial-accelerometer to quantify and compare: a) The most demanding passages of play in training sessions and matches (5-min peaks); b) and the accumulated load of typical microcycles and official matches, by playing position. Players performance data in 15 official home matches and 11 in-season microcycles were collected for analysis. Players were divided into four different playing positions: Centre-backs, wing-backs, centre midfielders, and centre forwards. The results show that match demands were overperformed for acceleration counts (acccounts) (131%-166%) and deceleration counts (deccounts) (108%-134%), by all positions. However, relative to match values, training values for sprint distance (sprintdist) and high-intensity run distance (HIRdist) were considerably lower (36%-61% and 57%-71%) than for accelerations and decelerations. The most pronounced difference on the 5-min peaks was observed in sprints (sprintpeak), with wing-backs achieving during the microcycle only 64% of the sprintpeak in matches, while centre backs, centre midfielders, and centre forwards levelled and overperformed the match values (107%, 100%, and 107%, respectively). Differences observed across playing positions in matches and microcycles underline the lack of position specificity of common training drills/sessions adopted by coaches in elite football.

#10 Why do football clubs fail financially? A financial distress prediction model for European professional football industry
Reference: PLoS One. 2019 Dec 26;14(12):e0225989. doi: 10.1371/journal.pone.0225989. eCollection 2019.
Authors: Alaminos D, Fernández MÁ
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Summary: The study of financial distress has been the focus of financial research in recent decades and has led to the development of models for predicting financial distress that help assess the financial situation and the risks faced by companies. These models have focused exclusively on industrial and financial companies. However, a specific model that reflects the special characteristics of the football industry has not yet been created. Since recently the governing bodies of the football industry have increased the financial control of the clubs, as in the case of UEFA with the approval of the Financial Fair Play Regulation and demand a pronouncement on going concern in the annual financial statements of clubs as well as presenting a break-even deficit caused by losses, it seems necessary to have a model adapted to the characteristics of this industry. The present study provides a new model of prediction of financial distress for the football industry with an accuracy that exceeds 90%. It also offers a vision of the challenges facing the football industry in financial matters, helping the different interest groups to assess the financial solvency expectations of the clubs.

#11 A multilevel hypernetworks approach to capture meso-level synchronisation processes in football
Reference: J Sports Sci. 2019 Dec 26:1-9. doi: 10.1080/02640414.2019.1707399. [Epub ahead of print]
Authors: Ribeiro J, Lopes R, Silva P, Araújo D, Barreira D, Davids K, Ramos J, Maia J, Garganta J
Summary: Understanding team behaviours in sports performance requires understanding the interdependencies established between their levels of complexity (micro-meso-macro). Previously, most studies examined interactions emerging at micro- and macro-levels, thus neglecting those emerging at a meso-level (reveals connections between player and team levels, depicted by the emergence of coordination in specific sub-groups of players-simplices during performance). We addressed this issue using the multilevel hypernetworks approach, adopting a cluster-phase method, to record player-simplice synchronies in two performance conditions where the number, size and location of goals were manipulated (first-condition: 6 × 6 + 4 mini-goals; second-condition: Gk + 6 × 6 + Gk). We investigated meso-level coordination tendencies, as a function of ball-possession (attacking/defending), field-direction (longitudinal/lateral) and teams (Team A/Team B). Generally, large synergistic relations and more stable patterns were observed in the longitudinal direction of the field than the lateral direction for both teams, and for both game phases in the first condition. The second condition displayed higher synchronies and more stable patterns in the lateral direction than the longitudinal plane for both teams, and for both game phases. Results suggest: (i) usefulness of hypernetworks in assessing synchronisation of teams at a meso-level; (ii) coaches may consider manipulating these task constraints to develop levels of local synchronies within teams.

#12 Differences in Technical Performance of Players From 'The Big Five' European Football Leagues in the UEFA Champions League
Reference: Front Psychol. 2019 Dec 6;10:2738. doi: 10.3389/fpsyg.2019.02738. eCollection 2019.
Authors: Yi Q, Groom R, Dai C, Liu H, Gómez Ruano MÁ
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Summary: The current study aimed to identify the differences in technical performance between players from clubs of Bundesliga (Germany), La Liga (Spain), Ligue 1 (France), Premier League (England) and Serie A (Italy) when competing in the matches of the UEFA Champions League. Technical performance-related match data of 1,291 players from 1,125 matches (9,799 observations) of the UEFA Champions League (seasons 2009/2010-2017/2018) were collected and analysed. The generalised mixed linear modelling was employed taking the names of the league as the independent variable to predict the count number of 20 technical performance-related match actions and events performed by players belonging to different leagues. The non-clinical magnitude-based inference was used to evaluate the uncertainty in the true effects of the predictor. Results showed that differences in the technical performances between players from La Liga, Premier League and Ligue 1 were all trivial. Bundesliga players made higher numbers of shots than players from La Liga, Premier League and Serie A and achieved more long balls than players from Ligue 1. Serie A players achieved lower numbers of ball touches, passes and lower pass accuracy per match than players from any of the other four leagues. In addition, players from Serie A performed a higher number of long balls per match than Ligue 1 players and lower number of dribbles per match than Premier League players. Non-significant differences in other variables related to passing and organising and all variables related to defending were identified in players between the five leagues. The identified differences in technical performance among leagues could provide a more thorough understanding for practitioners working within the fields of talent identification, player development, player recruitment, coaching and match preparation.





Latest research in football - week 53 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Attitudes and behavior related to performance-enhancing substance use among elite Saudi football players
Reference: BMC Sports Sci Med Rehabil. 2019 Dec 5;11:35. doi: 10.1186/s13102-019-0149-1. eCollection 2019.
Authors: Al Ghobain M
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Summary: The purpose was to investigate the attitudes, beliefs and behavior related to performance enhancing substances (PES) use in elite Saudi football players. A cross-sectional survey was conducted. Using a systematic random sample of elite Saudi male football players, the standard World Anti-doping Agency (WADA) Social Science Research Package questionnaire was distributed to 408 players. The overall prevalence rate of PES use was 3.9%, with the overall prevalence rate of doping susceptibility 17.1%. PES use or doping susceptibility is strongly correlated but negatively associated with morality and cheating measures (p <  0.011, the estimate is - 0.139), threat or deterrence appraisal (p <  0.001, the estimate is - 0.301) and beliefs about the reference group's endorsement (p < 0.001, the estimate is - 0.213) but not with legitimacy perceptions (p = 0.513) and beliefs about the benefits of doping (p = 0.678). The strongest relationship was found between threat or deterrence appraisal (p < 0.001), and beliefs about the reference group's endorsement of PES use (p < 0.001). Morality and cheating measures, threat or deterrence appraisal and beliefs about the reference group's endorsement are the main predictors for PES use in Saudi Arabia.

#2 The Effect of 1600 μg Inhaled Salbutamol Administration on 30 m Sprint Performance Pre and Post a Yo-Yo Intermittent Running Test in Football Players
Reference: J Sports Sci Med. 2019 Nov 19;18(4):716-721. eCollection 2019 Dec.
Authors: Merlini M, Beato M, Marcora S, Dickinson J
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Summary: The purpose of the study was to investigate the effect of inhaling 1600 μg of salbutamol (SAL) on 30 m sprint before and after the Yo-Yo Intermittent Recovery test. In a randomised cross over single blind study 13 male non-asthmatic, football players volunteered (mean ± SD; age 18.1 ± 0.9 years; weight 69.5 ± 8.3 kg; height 1.78 ± 0.07 m). Participants completed two visits and were randomly assigned to either (SAL) or (PLA) treatment and performed a set of three sprints of 30 m before and after the Yo-Yo Intermittent Recovery Test (Yo-Yo IRT). Best sprint and mean sprint were analysed in addition to the distance covered during the Yo-Yo IRT; rating of perceived exertion and heart rate were collected at the end of each level completed. Repeated measures ANOVA were performed to investigate changes in performance between groups. Following the inhalation of supra-therapeutic salbutamol dose (1600 μg) neither 30 m sprint time (PLA 4.43 ± 0.14 s; SAL 4.44 ± 0.15 s, p = 0.76) nor distance covered in the Yo-Yo IRT test reported significant variation between PLA conditions (1660 ± 217 m) and SAL (1610 ± 229 m, p = 0.16). Moreover, lactate values, heart rate and RPE did not differ significantly between groups. The inhalation of 1600 μg salbutamol does not enhance 30 m sprint performance in non-fatigued and fatigue conditions. Our findings suggest when football players acutely inhale double the permitted dose of salbutamol, as indicated in the World Anti-Doping Agency List of Prohibited Substances and Methods, they will not experience improvements in sprint or endurance performance.

#3 The Physiological, Physical, and Biomechanical Demands of Walking Football: Implications for Exercise Prescription and Future Research in Older Adults
Reference: J Aging Phys Act. 2019 Dec 10:1-11. doi: 10.1123/japa.2019-0330. [Epub ahead of print]
Authors: Harper LD, Field A, Corr LD, Naughton RJ.
Summary: The aim of this investigation was to profile the physiological, physical, and biomechanical responses during walking football. A total of 17 male participants (aged 66 ± 6 years) participated. Heart rate; blood lactate; accelerometer variables (biomechanical load [PlayerLoad™], changes of direction); and rating of perceived exertion were measured. Participants mean percentage of maximum heart rate was 76 ± 6% during the sessions, with rating of perceived exertion across all sessions at 13 ± 2. Blood lactate increased by ∼157% from presession (1.24 ± 0.4 mmol/L) to postsession (3.19 ± 1.7 mmol/L; p ≤ .0005). PlayerLoad™ values of 353 ± 67 arbitrary units were observed, as well as ∼100 changes of direction per session. In conclusion, walking football is a moderate- to vigorous-intensity activity. The longitudinal health benefits of walking football remain to be elucidated, particularly on bone health, cardiovascular fitness, and social and mental well-being.

#4 Experiences Influencing Walking Football Initiation in 55- to 75-Year-Old Adults: A Qualitative Study
Reference: J Aging Phys Act. 2019 Dec 10:1-13. doi: 10.1123/japa.2019-0123. [Epub ahead of print]
Authors: Cholerton R, Breckon J, Butt J, Quirk H.
Summary: Adults aged 55 and older are least likely to play sport. Despite research suggesting this population experiences physical and psychological benefits when doing so, limited research focuses on older adult sport initiation, especially in "adapted sports" such as walking football. The aim of this study was to explore initiation experiences of walking football players between 55 and 75 years old. Semistructured interviews took place with 17 older adults playing walking football for 6 months minimum (Mage = 64). Inductive analysis revealed six higher order themes representing preinitiation influences. Eight further higher order themes were found, relating to positive and negative experiences during initiation. Fundamental influences preinitiation included previous sporting experiences and values and perceptions. Emergent positive experiences during initiation included mental development and social connections. Findings highlight important individual and social influences when initiating walking football, which should be considered when encouraging 55- to 75-year-old adults to play adapted sport. Policy and practice recommendations are discussed.

#5 The 11+ Kids warm-up programme to prevent injuries in young Iranian male high-level football (soccer) players: A cluster-randomised controlled trial
Reference: J Sci Med Sport. 2019 Dec 9. pii: S1440-2440(19)30140-9. doi: 10.1016/j.jsams.2019.12.001. [Epub ahead of print]
Authors: Zarei M, Abbasi H, Namazi P, Asgari M, Rommers N, Rössler R
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Summary: The purpose was to assess the effectiveness of the 11+ Kids warm-up programme regarding injury reduction in male high-level children's football players. Male youth football teams of Iran's high-level football schools were invited to participate. Inclusion criteria were: teams are competing in the highest league of their province; players are between 7 and 14 years old; regular training takes place at least twice per week. Teams were excluded if they used an injury prevention measure. Participating clubs were randomised to an intervention (INT, N = 20 teams) and a control group (CON, N = 22 teams), stratified by the number of teams and the age group. The groups were blinded against each other. The follow-up period was one season (9 months). INT replaced their warm-up by 11+ Kids. CON performed a standard warm-up programme. The primary outcome was the injury incidence density (injuries per 1000 h of football exposure), compared between groups by incidence rate ratios (RR). In total, 64,047 h of football exposure of 962 players (INT = 443 players, 31,934 h of football, CON = 519 players, 32,113 h of football) were recorded. During the study, 90 (INT = 30; CON = 60) injuries occurred. The overall injury incidence density in INT was reduced by 50% compared to CON (RR 0.50; 95%-CI 0.32, 0.78). No injuries occurred during the execution of the intervention exercises. The 11+ Kids reduces injuries in high-level children's football players, thus supporting player health and potentially performance and player development.

#6 Strategic rule breaking: Time wasting to win soccer games
Reference: PLoS One. 2019 Dec 18;14(12):e0224150. doi: 10.1371/journal.pone.0224150. eCollection 2019.
Authors: Greve HR, Rudi N, Walvekar A
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Summary: Rules regulate behavior, but in competitive contexts they also create incentives for rule-breaking because enforcement is imperfect. Sports is a prime example of this, and one that lends itself well to investigation because strategic rule-breaking is often measurable. Professional soccer is a highly competitive team sport with economic rewards for winning given to teams and players. It has a set of rules to ensure fair play, but the enforcement is incomplete, and hence can lead to strategic behavior. Using newly available data, we examine strategic time-wasting, a behavior that help teams win games, or tie games against superior opponents, but is contrary to the objective of game play as entertainment for the spectators. We demonstrate that strategic time-wasting is widespread and is done through delayed restart of the game after goalie capture of the ball, goal kick, throw-in, free kick, corner kick, and substitution. The strategic time-wasting has substantial magnitude, and models of the value per minute predict time-wasting well. Because this time-wasting is a result of incentives created by not stopping the game clock, we predict that a change to rules with stopped game clock when the play is stopped would make game play more time efficient.

#7 Hidden dynamics of soccer leagues: The predictive 'power' of partial standings
Reference: PLoS One. 2019 Dec 18;14(12):e0225696. doi: 10.1371/journal.pone.0225696. eCollection 2019.
Authors: Beggs CB, Bond AJ, Emmonds S, Jones B
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Summary: Soccer leagues reflect the partial standings of the teams involved after each round of competition. However, the ability of partial league standings to predict end-of-season position has largely been ignored. Here we analyze historical partial standings from English soccer to understand the mathematics underpinning league performance and evaluate the predictive 'power' of partial standings. Match data (1995-2017) from the four senior English leagues was analyzed, together with random match scores generated for hypothetical leagues of equivalent size. For each season the partial standings were computed and Kendall's normalized tau-distance and Spearman r-values determined. Best-fit power-law and logarithmic functions were applied to the respective tau-distance and Spearman curves, with the 'goodness-of-fit' assessed using the R2 value. The predictive ability of the partial standings was evaluated by computing the transition probabilities between the standings at rounds 10, 20 and 30 and the final end-of-season standings for the 22 seasons. The impact of reordering match fixtures was also evaluated. All four English leagues behaved similarly, irrespective of the teams involved, with the tau-distance conforming closely to a power law (R2>0.80) and the Spearman r-value obeying a logarithmic function (R2>0.87). The randomized leagues also conformed to a power-law, but had a different shape. In the English leagues, team position relative to end-of-season standing became 'fixed' much earlier in the season than was the case with the randomized leagues. In the Premier League, 76.9% of the variance in the final standings was explained by round-10, 87.0% by round-20, and 93.9% by round-30. Reordering of match fixtures appeared to alter the shape of the tau-distance curves. All soccer leagues appear to conform to mathematical laws, which constrain the league standings as the season progresses. This means that partial standings can be used to predict end-of-season league position with reasonable accuracy.

#8 Positive fantasies and negative emotions in soccer fans
Reference: Cogn Emot. 2019 Dec 17:1-12. doi: 10.1080/02699931.2019.1703649. [Epub ahead of print]
Authors: Sevincer AT, Wagner G, Oettingen G
Summary: Positive thinking is often assumed to foster effort and success. Research has shown, however, that positive thinking in the form of fantasies about achieving an idealised future predicts less (not more) effort and success and more (not less) depressive symptoms over time. This relationship was mediated by people having invested little effort and achieved little success. Here, we ask a different question. We investigate the emotional consequences of positive fantasies about futures that people cannot act on. Specifically, we analyse these consequences when the future fantasies fail to come true (one's favourite soccer team loses). Study 1 provided correlational evidence. The more positively soccer fans fantasised about their favourite team winning an upcoming match, the stronger were their negative emotions when their team lost. That is, the more sad, disappointed, and frustrated they felt. Study 2 provided experimental evidence. Soccer fans who were led to fantasise positively about their team winning an upcoming match reported feeling stronger negative emotions after their team lost than those who were led to fantasise negatively. Positive fantasies were not related to how positive participants felt after their team won (joy, happiness, relief). We discuss theoretical and applied implications for emotion regulation in everyday life.

#9 Half Soccer Season Induced Physical Conditioning Adaptations in Elite Youth Players
Reference: Int J Sports Med. 2019 Dec 16. doi: 10.1055/a-1014-2809. [Epub ahead of print]
Authors: Arregui-Martin MA, Garcia-Tabar I, Gorostiaga EM
Summary: This study aimed to investigate training-induced fitness changes and their relationship with training-competition load during half a soccer season (18 wks). Training load [heart rate (HR) and ratings of perceived exertion (RPE)] and match time were monitored, including 108 training (3 223 individuals) and 23 match sessions, in 38 youth elite male soccer players. Fitness variables were assessed before and after the study. Yo-Yo intermittent recovery test 1 (Yo-Yo IRT1) improved (P<0.001; 90%CI: 418-632 m; ES: 2.14). Anthropometrical, jump, sprint, and change-of-direction measures remained unchanged. Jump test correlated with sprint (r=0.74; P<0.001; SEE=3.38 m·s-1) and Yo-Yo IRT1 (r=-0.58; P=0.005; SEE=4.11 m) tests. Initial sum of 6 skinfolds was associated with changes in this same measure (r=-0.51; P<0.001; SEE=21%). Initial Yo-Yo IRT1 results were related to changes in Yo-Yo IRT1 (r=-0.84; P<0.001; SEE=10%) and match time played (r=0.44; P=0.033; SEE=445 m). Mean RPE records were related to training spent within 75-90% maximal HR (r=0.54; P<0.001; SEE=4%). The half-season was beneficial for endurance running performance but not for lower-limb strength-velocity production capacity. The more aerobically deconditioned players played fewer minutes of match, although they showed the greatest improvements in endurance performance. Non-soccer-specific, scientifically based, and individualized fitness programs in addition to soccer-specific training are recommended.

#10 Oculomotor Control in Amputee Soccer Players
Reference: Adapt Phys Activ Q. 2019 Dec 14:1-15. doi: 10.1123/apaq.2019-0028. [Epub ahead of print]
Authors: Jedziniak W, Lesiakowski P, Zwierko T
Summary: The authors investigated the dynamics of saccadic parameters during a stationary oculomotor target task in amputee soccer players (n = 16), able-bodied soccer players (n = 16), and nonathletic control subjects (n = 16). Eye movements during the visual-search tasks were recorded binocularly using a mobile eye-tracking system, and the gaze parameters were analyzed (fixation duration, saccade duration, saccade amplitude, saccade average acceleration, saccade peak deceleration, saccade average velocity, and ocular mobility index). The average saccade acceleration in the amputee soccer players was significantly lower than in the able-bodied players (p = .021). Other saccade characteristics in disabled athletes were comparable to those of the able-bodied groups. Moreover, the able-bodied soccer players presented faster saccadic parameters than nonathletes in terms of saccade acceleration (p = .002), deceleration (p = .015), and velocity (p = .009). The modification of oculomotor functions may result from extensive practice and participation in ball games. The authors' hypothesis that oculomotor functions in amputee soccer players may be impaired was not fully confirmed.

#11 Prevalence and severity of groin problems in Spanish football: A prospective study beyond the time-loss approach
Reference: Scand J Med Sci Sports. 2019 Dec 17. doi: 10.1111/sms.13615. [Epub ahead of print]
Authors: Esteve E, Clausen MB, Rathleff MS, Vicens-Bordas J, Casals M, Palahí-Alcàcer A, Hölmich P, Thorborg K
Summary: The time-loss definition of injury is commonly adopted in epidemiological groin-injury studies in football, with a significant risk of underestimating the impact of these injuries. This study investigated the extent of groin problems, beyond the time-loss approach, over a full Spanish football season. Players from 17 amateur male teams were followed over 39 consecutive weeks. Groin-injury time loss and self-reported groin pain, irrespective of time loss, were combined to calculate the average weekly prevalence of all groin problems with or without time loss. A subscale measuring hip- and groin-related sporting function from the Copenhagen Hip And Groin Outcome Score questionnaire (HAGOS, Sport/Rec) was registered every 4 weeks. In total, 407 players participated in the study. The average (range) weekly prevalence of all groin problems was 11.7% (7.2-20.8%); 1.3% with time loss (0.0-3.2%) and 10.4% without time loss (6.3-17.6%). Players with groin problems reported lower scores (mean difference) on the HAGOS, Sport/Rec subscale compared to players without (-19.5 (95% CI: -20.7 - -18.4), while there was no difference between players reporting groin problems with and without time loss (4.0 (95% CI: -1.1 - 9.1). The traditional time-loss measure only captured 10% of all groin problems. Hip- and groin-related sporting function was not different between players reporting groin problems with or without time loss, suggesting the reason for continuing to play is not only related to the severity of symptoms. These findings question the judicious use of the time-loss approach in overuse conditions, such as groin pain in footballers.

#12 Electrocardiographic and Echocardiographic Findings in Elite Ghanaian Male Soccer Players
Reference: Clin J Sport Med. 2019 Dec 24. doi: 10.1097/JSM.0000000000000801. [Epub ahead of print]
Authors: Pambo P, Adu-Adadey M, Agbodzakey H, Scharhag J
Summary: The purpose was to analyze the athlete's heart of adult and adolescent elite male soccer players by electrocardiography (ECG) and echocardiography (ECHO) and to describe typical ECG and ECHO findings in this cohort (West African elite soccer players). A cross-sectional study of ECGs and ECHOs conducted as part of precompetition medical assessment for national male soccer teams preparing for various Fédération Internationale de Football Association (FIFA) tournaments in 2016 and 2017. One hundred fifty-nine players playing for the National male soccer teams preparing for tournaments in 2016 and 2017 participated in this study. Number of athletes with abnormal ECGs and ECHO findings were used as main outcome measures. Twenty-three percent of the players had abnormal ECGs. Nine percent of the participants had T-wave inversions in lateral leads (V5-V6). Sokolow-Lyon criteria for left ventricular hypertrophy were present in 64% of participants. Thirty-six (23%) players had left ventricular wall thickness (LVWT) ≥13 mm, with no player exceeding 16 mm. Four percent of players had left ventricular cavity dimension greater than 60 mm. Relative wall thickness >0.42 was present in 44% of the players. Uncommon ECG changes seem to be more common in elite Ghanaian soccer players compared with previously reported results for Caucasians and even mixed populations of black athletes. Although ST elevation, T-wave inversions, and LVWT up to 15 mm are common, ST depression, deep T-waves in lateral leads, and LVWT ≥16 mm always warrant further clinical and scientific investigations.





Latest research in football - week 52 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Comparing the Aerobic Fitness of Professional Male Soccer Players and Soccer Referees
Reference: Curr Sports Med Rep. 2019 Dec;18(12):497-501. doi: 10.1249/JSR.0000000000000668.
Authors: Santos-Silva PR, D'Andrea Greve JM, Pedrinelli A, Almeida AM, Osorio BB, Ferreira M, Ferreira C
Summary: We looked to compare the aerobic performance between professional soccer referees and players. Fifty male soccer referees and 61 male soccer players were tested on a treadmill. The referees and players possessed 15 ± 7 years and 7 ± 3 years of experience in soccer, respectively. Significant differences were observed between the referees and players with regards to: age (34.8 ± 4.6 years vs 20.8 ± 2.7 years; P < 0.001, maximum oxygen uptake (54.7 ± 5.4 mL·kg·min vs 58.8 ± 4.4 mL·kg·min; P < 0.001), and maximal heart rate in peak exercise (184 ± 11 bpm vs 192 ± 9 bpm, P < 0.001). Less significant differences also were observed and included; running speed at the maximum oxygen uptake (16.6 ± 1 km·h vs 16.4 ± 1.1 km·h), running speed at the ventilatory threshold (213.5 ± 1.1 km·h vs 13.2 ± 0.9 km·h), and percentage of maximal oxygen uptake at the ventilatory threshold (285.1% ± 3.2% vs 84.1% ± 6.2%). The effect size of most comparative variables between the two groups was small (<0.6). Older elite-level soccer referees are able to reach and maintain aerobic physical fitness levels similar to professional soccer players. Aerobic physical fitness may be a measurable factor for maintaining elite-level soccer licensure rather than age alone.

#2 Scapula Fractures in Elite Soccer and Rugby Players
Reference: Orthop J Sports Med. 2019 Dec 2;7(12):2325967119887388. doi: 10.1177/2325967119887388. eCollection 2019 Dec.
Authors: McIntosh J, Akhbari P, Malhas A, Funk L
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Summary: Scapula fractures are uncommon in sports and are poorly understood in this patient group. The purpose was to report on scapula fractures in contact and collision athletes and assess the injury patterns of different mechanisms of injury. A retrospective case series was performed of all sports-related scapula fractures treated at a single institution between 2007 and 2015. The mechanisms of injury were divided into direct lateral impact, fall onto an outstretched arm, or abduction/external rotation. A total of 11 patients were identified: 9 professional rugby players, 1 professional soccer player, and 1 amateur soccer player. The mean age was 28 years (range, 18-35 years). The mean return to play was 127 days in those treated nonoperatively and 163 days in those treated operatively. A direct impact mechanism occurred in 7 patients, all of whom sustained glenoid neck and body fractures and were treated nonoperatively. Two rugby players had a concomitant suprascapular nerve injury. An outstretched arm mechanism occurred in 2 cases, leading to posterior and inferior glenoid fractures. Both patients were treated operatively. An abduction/external rotation mechanism occurred in 2 cases, resulting in an anteroinferior and an anterior glenoid rim fracture. One case was treated operatively and the other was treated nonoperatively. Of those with glenoid fractures, 75% were not visible on plain radiographs and required further imaging. Scapula fractures acquired in sports are a serious injury with a prolonged recovery period. The mechanism of injury can help predict the injury pattern and highlight the need for further imaging. There is a high association with suprascapular nerve injuries.

#3 Infrared Low-Level Laser Therapy (Photobiomodulation Therapy) before Intense Progressive Running Test of High-Level Soccer Players: Effects on Functional, Muscle Damage, Inflammatory, and Oxidative Stress Markers-A Randomized Controlled Trial
Reference: Oxid Med Cell Longev. 2019 Nov 16;2019:6239058. doi: 10.1155/2019/6239058. eCollection 2019.
Authors: Tomazoni SS, Machado CDSM, De Marchi T, Casalechi HL, Bjordal JM, de Carvalho PTC, Leal-Junior ECP
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Summary: The effects of preexercise photobiomodulation therapy (PBMT) to enhance performance, accelerate recovery, and attenuate exercise-induced oxidative stress were still not fully investigated, especially in high-level athletes. The aim of this study was to evaluate the effects of PBMT (using infrared low-level laser therapy) applied before a progressive running test on functional aspects, muscle damage, and inflammatory and oxidative stress markers in high-level soccer players. A randomized, triple-blind, placebo-controlled crossover trial was performed. Twenty-two high-level male soccer players from the same team were recruited and treated with active PBMT and placebo. The order of interventions was randomized. Immediately after the application of active PBMT or placebo, the volunteers performed a standardized high-intensity progressive running test (ergospirometry test) until exhaustion. We analyzed rates of oxygen uptake (VO2 max), time until exhaustion, and aerobic and anaerobic threshold during the intense progressive running test. Creatine kinase (CK) and lactate dehydrogenase (LDH) activities, levels of interleukin-1β (IL-1-β), interleukin-6 (IL-6), and tumor necrosis factor alpha (TNF-α), levels of thiobarbituric acid (TBARS) and carbonylated proteins, and catalase (CAT) and superoxide dismutase (SOD) activities were measured before and five minutes after the end of the test. PBMT increased the VO2 max (both relative and absolute values-p < 0.0467 and p < 0.0013, respectively), time until exhaustion (p < 0.0043), time (p < 0.0007) and volume (p < 0.0355) in which anaerobic threshold happened, and volume in which aerobic threshold happened (p < 0.0068). Moreover, PBMT decreased CK (p < 0.0001) and LDH (p < 0.0001) activities. Regarding the cytokines, PBMT decreased only IL-6 (p < 0.0001). Finally, PBMT decreased TBARS (p < 0.0001) and carbonylated protein levels (p < 0.01) and increased SOD (p < 0.0001)and CAT (p < 0.0001) activities. The findings of this study demonstrate that preexercise PBMT acts on different functional aspects and biochemical markers. Moreover, preexercise PBMT seems to play an important antioxidant effect, decreasing exercise-induced oxidative stress and consequently enhancing athletic performance and improving postexercise recovery.

#4 Effects of a 6-Week Strength Training of the Neck Flexors and Extensors on the Head Acceleration during Headers in Soccer
Reference: J Sports Sci Med. 2019 Nov 19;18(4):729-737. eCollection 2019 Dec.
Authors: Becker S, Berger J, Backfisch M, Ludwig O, Kelm J, Fröhlich M
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Summary: The importance of well trained and stable neck flexors and extensors as well as trunk muscles for intentional headers in soccer is increasingly discussed. The neck flexors and extensors should ensure a coupling of trunk and head at the time of ball contact to increase the physical mass hitting the ball and reduce head acceleration. The aim of the study was to analyze the influence of a 6-week strength training program (neck flexors, neck extensors) on the acceleration of the head during standing, jumping and running headers as well as after fatigue of the trunk muscles on a pendulum header. A total of 33 active male soccer players (20.3 ± 3.6 years, 1.81 ± 0.07 m, 75.5 ± 8.3 kg) participated and formed two training intervention groups (IG1: independent adult team, IG2: independent youth team) and one control group (CG: players from different teams). The training intervention consisted of three exercises for the neck flexors and extensors. The training effects were verified by means of the isometric maximum voluntary contraction (IMVC) measured by a telemetric Noraxon DTS force sensor. The head acceleration during ball contact was determined using a telemetric Noraxon DTS 3D accelerometer. There was no significant change of the IMVC over time between the groups (F=2.265, p=.121). Head acceleration was not reduced significantly for standing (IG1 0.4 ± 2.0, IG2 0.1 ± 1.4, CG -0.4 ± 1.2; F = 0.796, p = 0.460), jumping (IG1-0.7 ± 1.4, IG2-0.2 ± 0.9, CG 0.1 ± 1.2; F = 1.272, p = 0.295) and running (IG1-1.0 ± 1.9, IG2-0.2 ± 1.4, CG -0.1 ± 1.6; F = 1.050, p = 0.362) headers as well as after fatigue of the trunk musculature for post-jumping (IG1-0.2 ± 2.1, IG2-0.6 ± 1.4; CG -0.6 ± 1.3; F = 0.184, p = 0.833) and post-running (IG1-0.3 ± 1.6, IG2-0.7 ± 1.2, CG 0.0 ± 1.4; F = 0.695, p = 0.507) headers over time between IG1, IG2 and CG. A 6-week strength training of the neck flexors and neck extensors could not show the presumed preventive benefit. Both the effects of a training intervention and the consequences of an effective intervention for the acceleration of the head while heading seem to be more complex than previously assumed and presumably only come into effect in case of strong impacts.

#5 Monitoring the Athlete Match Response: Can External Load Variables Predict Post-match Acute and Residual Fatigue in Soccer? A Systematic Review with Meta-analysis
Reference: Sports Med Open. 2019 Dec 9;5(1):48. doi: 10.1186/s40798-019-0219-7.
Authors: Hader K, Rumpf MC, Hertzog M, Kilduff LP, Girard O, Silva JR
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Summary: Monitoring athletes' external load during a soccer match may be useful to predict post-match acute and residual fatigue. This estimation would allow individual adjustments to training programs to minimize injury risk, improve well-being, and restore players' physical performance and inform the recovery process. Using a systematic review and meta-analysis of the literature, the aim is to determine which monitoring variables would be the strongest predictors of acute (immediately) and residual (up to 72 h) fatigue states in soccer. PubMed, SPORTDiscus, and Web of Science databases were searched (until September 2018). Studies concurrently examining soccer match-related external load metrics and subjective and/or objective measures were selected to determine pooled correlations ([Formula: see text]) with confidence intervals (CI). The quality and strength of the findings of each study were evaluated to identify overall levels of evidence. Eleven studies were included (n = 165 athletes). Acute ([Formula: see text] = 0.67; 95% CI = [0.40, 0.94]) and residual (24 h post-match, [Formula: see text] = 0.54; 95% CI = [0.35, 0.65]) changes in muscle damage markers and countermovement jump peak power output (CMJPPO) were, with moderate to strong evidence, largely correlated with running distance above 5.5 m s-1. No other external load metric was largely correlated with both biochemical and neuromuscular markers. For every 100-m run above 5.5 m·s-1, CK activity measured 24 h post-match increased by 30% and CMJPPO decreased by 0.5%. Conversely, the total distance covered did not present any evidence of a clear relationship with any fatigue-related marker at any time-point. Running distance above 5.5 m·s-1 represents the most sensitive monitoring variable characterizing biochemical and neuromuscular responses, at least when assessed during the initial 24 h (not at 48 h/72 h) post-match recovery period. In addition, total distance covered is not sensitive enough to inform decision-making during the fatigue monitoring process.

#6 A bioecological perspective on talent identification in junior-elite soccer: A Pan-European perspective
Reference: J Sports Sci. 2019 Dec 9:1-10. doi: 10.1080/02640414.2019.1702282. [Epub ahead of print]
Authors: Reeves MJ, Roberts SJ
Summary: Elite soccer clubs across Europe spend ever-increasing sums of money on transfers and salaries for world-class players. Consequently, clubs' talent identification and development processes for junior players have become more professionalised. Based on a holistic ecological approach, this study presents an analysis of talent identification practices across some of the most productive soccer academies in Europe (N = 11). Data were collected via semi-structured interviews with 11 heads of academy recruitment from clubs in the "big five" European leagues. Clubs were purposively sampled based on their player productivity ranking. Interviews ranged from 52:26 minutes to 114:06 minutes in length (m = 87:53 ± 20.10 minutes). This study argues that holistic ecological approaches the environments were characterised through the interplay of factors that ranged from high-level internal to international level relationships. This resulted in the identification and recruitment of players from local and international environments. The purpose of recruitment was suggested to have a dual purpose: recruitment of players for the first team; recruitment of players for further development/monitoring and/or selling to another club.

#7 Endocrine Responses to Various 1 × 1 Small-Sided Games in Youth Soccer Players
Reference: Int J Environ Res Public Health. 2019 Dec 6;16(24). pii: E4974. doi: 10.3390/ijerph16244974.
Authors: Chmura P, Podgórski T, Konefał M, Rokita A, Chmura J, Andrzejewski M
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Summary: The aim of this study was to determine relationships between repeated 1 × 1 small-sided games (SSGs) (variable duration, constant work-to-rest ratio) and the concentration of steroid hormones and characteristic fatigue markers in youth soccer players. Eighteen young male soccer players were assigned at random to two experimental groups: E1-undertaking a six 30 s one-on-one SSGs with a 2 min rest period; and E2-playing six 45 s SSGs with a 3 min rest interval. Capillary blood was collected from the players at rest, after the last game, and 15 and 30 min after the exercise protocol. The variables assessed included serum cortisol (C), free testosterone (FT) and total testosterone (TT). An effect was observed between the measurement times (TT (F = 15.26, p ≤ 0.0001), FT (F = 6.86, p = 0.0006)). In terms of cortisol (C) levels, no interactions or effect between the studied groups were revealed, but an interaction was found (F = 4.01, p = 0.0126) and the effect appeared between the measurement times (F = 11.16, p ≤ 0.0001). The study results show that in all likelihood, longer rest intervals in repeated 30 s 1 × 1 SSGs can reduce catabolic reactions and hence the risk of overtraining in youth soccer players.

#8 Interactive Improvements of Visual and Auditory Function for Enhancing Performance in Youth Soccer Players
Reference: Int J Environ Res Public Health. 2019 Dec 5;16(24). pii: E4909. doi: 10.3390/ijerph16244909.
Authors: Song YH, Ha SM, Yook JS, Ha MS
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Summary: We analyzed the effects of a regular training program on the health- and skill-related physical fitness (PF) of talented soccer players aged < 12 years; visual reaction time (VRT) and auditory reaction time (ART) were also assessed. In this single-group interventional study, 78 talented male youth soccer players (mean age, 9.54 years) were critically selected by the Korean Educational Development Institute and underwent a 22-week training program consisting of 16 weeks of PF and basic skill training (90 min/week) and 6 weeks of intensive training (3, 150-min sessions/week). We assessed the pre- and post-training body composition, cardiovascular endurance, muscle strength and endurance, and flexibility. We also measured power, agility, coordination and speed, passing ability, VRT, and ART. All variables improved after training. Post-training VRT correlated with ART, muscle mass, power, cardiovascular endurance, 10-m dribble time, 10-m ball touch count, and 10-m successful pass count. ART only correlated with muscle mass. ART and 10-m ball-touch count influenced VRT, and VRT influenced ART. In conclusion, the training program enhanced the PF and visual- and auditory-related reactions in talented youth soccer players. This study suggests the importance of the assessed relationships, indicating that a training program that improves these parameters enhances the players' performance.

#9 Effect of Training Load on Post-Exercise Cardiac Troponin T Elevations in Young Soccer Players
Reference: Int J Environ Res Public Health. 2019 Dec 2;16(23). pii: E4853. doi: 10.3390/ijerph16234853.
Authors: Cirer-Sastre R, Legaz-Arrese A, Corbi F, López-Laval I, Puente-Lanzarote J, Hernández-González V, Reverter-Masià J
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Summary: Training load (TL) metrics are usually assessed to estimate the individual, physiological and psychological, acute, and adaptive responses to training. Cardiac troponins (cTn) reflect myocardial damage and are routinely analyzed for the clinical diagnosis of myocardial injury. The association between TL and post-exercise cTn elevations is scarcely investigated in young athletes, especially after playing common team sports such as soccer. The objective of this study was to assess the relationship between TL measurements during a small-sided soccer game and the subsequent increase in cTn in young players. Twenty male soccer players (age 11.9 ± 2 years, height 151 ± 13 cm, weight 43 ± 13 kg) were monitored during a 5 × 5 small-sided game and had blood samples drawn before, immediately after, and 3 h after exercise for a posterior analysis of high-sensitivity cardiac troponin T (hs-cTnT). Internal, external, and mixed metrics of TL were obtained from the rating of perceived exertion (RPE), heart rate (HR), and GPS player tracking. The results show that the concentration of hs-cTnT peaked at 3 h post-exercise in all participants. The magnitude of hs-cTnT elevation was mainly explained by the exercise duration in the maximal heart rate zone (Maximum Probability of Effect (MPE) = 92.5%), time in the high-speed zone (MPE = 90.4 %), and distance in the high-speed zone (MPE = 90.45%). Our results support the idea that common metrics of TL in soccer, easily obtained using player tracking systems, are strongly associated with the release of hs-cTnT in children and adolescents.

#10 Recreational Football is Medicine against Non-Communicable Diseases: A systematic Review
Reference: Scand J Med Sci Sports. 2019 Dec 13. doi: 10.1111/sms.13611. [Epub ahead of print]
Authors: Sarmento H, Manuel Clemente F, Marques A, Milanovic Z, David Harper L, Figueiredo A
Summary: The purpose of this research was to conduct a systematic review of published articles related to the effect of recreational football on non-communicable diseases. A systematic review of Web of Science, SPORTdiscus, MEDLINE and PubMed databases was performed according PRISMA guidelines. Only empirical studies were included. There were no restrictions on the types of study design eligible for inclusion. The primary outcome measures result from the potential effects of recreational football on non-communicable diseases (e.g., blood pressure, bone density, LDL-Cholesterol, fat mass, etc.). A total of 44 articles met the inclusion criteria and were included. Recreational football is shown to: (1) decrease blood pressure and resting heart rate, improve cardiac structure and functioning, as well as increase maximal oxygen uptake in both sexes; (2) reduce cholesterol and triglycerides levels, increase insulin sensitivity, and have a positive impact on glycaemic control; (3) improve bone mineralization, increase both bone mineral density and content, as well as acting as a stimulus for osteogenesis; (4) be clearly beneficial for bone health, whilst slightly beneficial for body composition, muscle strength and maximal oxygen uptake in adults with prostate cancer. The present systematic review demonstrated the benefits of recreational football practice on non-communicable diseases related to cardiovascular and bone health, body composition, type 2 diabetes and prostate cancer. The effectiveness of recreational football on the aforementioned diseases may be related to age and gender; however, further research is required.





Latest research in football - week 51 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 The Effects of Lower-Extremity Plyometric Training on Soccer-Specific Outcomes in Adult Male Soccer Players: A Systematic Review and Meta-Analysis
Reference: Int J Sports Physiol Perform. 2019 Dec 4:1-15. doi: 10.1123/ijspp.2019-0565. [Epub ahead of print]
Authors: van de Hoef PA, Brauers JJ, van Smeden M, Backx FJG, Brink MS.
Summary: Plyometric training is a specific form of strength training that is used to improve the physical performance of athletes. An overview of the effects of plyometric training on soccer-specific outcomes in adult male soccer players is not available yet. The purpose was to systematically review and meta-analyze the effects of plyometric training on soccer-specific outcome measures in adult male soccer players and to identify which programs are most effective. PubMed, Embase/Medline, Cochrane, PEDro, and Scopus were searched. Extensive quality and risk of bias assessments were performed using the Cochrane ROBINS 2.0 for randomized trials. A random effects meta-analysis was performed using Cochrane Review Manager 5.3. Seventeen randomized trials were included in the meta-analysis. The impact of plyometric training on strength, jump height, sprint speed, agility, and endurance was assessed. Only jump height, 20-m sprint speed, and endurance were significantly improved by plyometric training in soccer players. Results of the risk of bias assessment of the included studies resulted in overall scores of some concerns for risk of bias and high risk of bias. This review and meta-analysis showed that plyometric training improved jump height, 20-m sprint speed, and endurance, but not strength, sprint speed over other distances, or agility in male adult soccer players. However, the low quality of the included studies and substantial heterogeneity means that results need to be interpreted with caution. Future high-quality research should indicate whether or not plyometric training can be used to improve soccer-specific outcomes and thereby enhance performance.

#2 The influence of playing position in soccer on the recovery kinetics of cognitive and physical performance
Reference: J Sports Med Phys Fitness. 2019 Nov;59(11):1812-1819. doi: 10.23736/S0022-4707.19.09433-7.
Authors: Nedelec M, Dupont G
Summary: The physical activity and playing actions performed during a soccer match vary according to player position. The aim of the present study was to analyze the recovery kinetics of cognitive performance, physical performance and subjective ratings after a competitive soccer match. Eight goalkeepers and eight outfield players played in the match with data collected before, 45 min, 24 h and 48 h after the match. Subjective ratings, Vienna Reaction Test (reaction time, motor time), Vienna Determination Test (number of stimuli, number of correct responses), squat jump, countermovement jump and 6-s sprint were analyzed. No significant interaction between position and time was found for Vienna Reaction Test and Vienna Determination Test performance. No significant interaction between position and time was found for squat jump and countermovement jump but squat jump and countermovement jump significantly decreased (P<0.01) at 24 h. Countermovement jump performance was still significantly affected at 48h (P<0.05). A significant interaction between position and time (P<0.05) was found for 6-s sprint. Sprint performance was significantly reduced for outfield players only immediately after the match (P<0.01). There was no interaction effect of position and time on subjective ratings. A significant correlation was found between number of jumps and ball kicks performed during the match by goalkeepers and the change score in squat jump (r =-0.90; P<0.01) and countermovement jump (r =-0.90; P<0.01) observed at 48 h. Outfield players require a longer time than goalkeepers to recover sprint performance whilst cognitive function tested in the present study is not affected by the match whatever the position.

#3 Accuracy of the functional movement screen (FMS) active straight leg raise test to evaluate hamstring flexibility in soccer players
Reference: Int J Sports Phys Ther. 2019 Dec;14(6):877-884.
Authors: Medeiros DM, Miranda LLP, Marques VB, de Araujo Ribeiro-Alvares JB, Baroni BM
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Summary: Poor flexibility is considered a risk factor for the hamstring strain injury, and the active straight leg raise (ASLR) test proposed as a part of the Functional Movement Screen™ (FMS™) has been used to assess athletes hamstring flexibility. However, the accuracy of this screening test remains undescribed. The purpose was to examine the accuracy of the FMS™ ASLR test for assessment of hamstring flexibility in soccer players. One-hundred and one male soccer players (age, 21 ± 3 years; height, 179 ± 7 cm; weight, 75 ± 9 kg) were bilaterally evaluated. All players performed a gold standard test for hamstring flexibility evaluation: the passive straight leg raise (PSLR) test measured using a gravitational inclinometer. All players also performed the ASLR test and were scored using the criteria proposed by the FMS™. Of the 202 lower limbs evaluated, 17.82% scored a 1 on the ASLR [mean passive flexibility: 80.44 ± 14.69 ° (55 °-110 °)], 50.99% scored a 2 on the ASLR [mean passive flexibility = 84.60 ± 10.59 ° (56 °-115 °)], and 31.18% scored a 3 on the ASLR [mean passive flexibility = 92.32 ± 11.53 ° (70 °-120 °)]. Limbs with FMS™ score of 3 presented significantly higher values for passive flexibility than limbs with scores of 1 and 2 (p < 0.05), but there was no significant difference between limbs with scores of 1 and 2 (p > 0.05). The score obtained in the FMS™ ASLR test does not satisfactorily stratify the level of hamstring flexibility in soccer players.

#4 Workload and Injury in Professional Soccer Players: Role of Injury Tissue Type and Injury Severity
Reference: Int J Sports Med. 2019 Dec 4. doi: 10.1055/a-0997-6741. [Epub ahead of print]
Authors: Enright K, Green M, Hay G, Malone JJ
Summary: The purpose of the present study was to examine the influence of workload prior to injury on injury (tissue type and severity) in professional soccer players. Twenty-eight days of retrospective training data prior to non-contact injuries (n=264) were collated from 192 professional soccer players. Each injury tissue type (muscle, tendon and ligament) and severity (days missed) were categorised by medical staff. Training data were recorded using global positioning system (GPS) devices for total distance (TD), high speed distance (HSD,>5.5 m/s-1), and sprint distance (SPR,>7.0 m/s-1). Accumulated 1, 2, 3, 4-weekly loads and acute:chronic workload ratios (ACWR) (coupled, uncoupled and exponentially weighted moving average (EWMA) approaches) were calculated. Workload variables and injury tissue type were compared using a one-way ANOVA. The association between workload variables and injury severity were examined using a bivariate correlation. There were no differences in accumulated weekly loads and ACWR calculations between muscle, ligament, and tendon injuries (P>0.05). Correlations between each workload variable and injury severity highlighted no significant associations (P>0.05). The present findings suggest that the ability of accumulated weekly workload or ACWR methods to differentiate between injury type and injury severity are limited using the present variables.

#5 Variations of training load, monotony, and strain and dose-response relationships with maximal aerobic speed, maximal oxygen uptake, and isokinetic strength in professional soccer players
Reference: PLoS One. 2019 Dec 4;14(12):e0225522. doi: 10.1371/journal.pone.0225522. eCollection 2019.
Authors: Clemente FM, Clark C, Castillo D, Sarmento H, Nikolaidis PT, Rosemann T, Knechtle B
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Summary: This study aimed to identify variations in weekly training load, training monotony, and training strain across a 10-week period (during both, pre- and in-season phases); and to analyze the dose-response relationships between training markers and maximal aerobic speed (MAS), maximal oxygen uptake, and isokinetic strength. Twenty-seven professional soccer players (24.9±3.5 years old) were monitored across the 10-week period using global positioning system units. Players were also tested for maximal aerobic speed, maximal oxygen uptake, and isokinetic strength before and after 10 weeks of training. Large positive correlations were found between sum of training load and extension peak torque in the right lower limb (r = 0.57, 90%CI[0.15;0.82]) and the ratio agonist/antagonist in the right lower limb (r = 0.51, [0.06;0.78]). It was observed that loading measures fluctuated across the period of the study and that the load was meaningfully associated with changes in the fitness status of players. However, those magnitudes of correlations were small-to-large, suggesting that variations in fitness level cannot be exclusively explained by the accumulated load and loading profile.

#6 A Comparison of Training Modality and Total Genotype Scores to Enhance Sport-Specific Biomotor Abilities in Under 19 Male Soccer Players
Reference: J Strength Cond Res. 2019 Nov 27. doi: 10.1519/JSC.0000000000003299. [Epub ahead of print]
Authors: Suraci BR, Quigley C, Thelwell RC, Milligan GS
Summary: Soccer-specific training (SST) and small-sided games (SSGs) have been shown to develop physical proficiency in soccer. Research on genetics and epigenetics in the prescription of training is limited. The aims of this study were to compare the impact of 3 different SST/SSG methods and investigate if a total genotype score (TGS) influences training response. Subjects (n = 30 male soccer players, mean ± SD; age 17.2 ± 0.9 years, stature = 172.6 ± 6.2 cm; body mass = 71.7 ± 10.1 kg) were stratified into a "power" (PG) or "endurance" (EG) gene profile group, where a 15 single nucleotide polymorphism panel was used to produce an algorithmically weighted TGS. Training 1 (T1-SSGs only), training 2 (T2-SSGs/SST), and training 3 (T3-SST only) were completed (in that respective order), lasting 8 weeks each, interspersed by 4-week washouts. Acceleration (10-m sprint) was improved by T2 only (1.84 ± 0.09 seconds vs. 1.73 ± 0.05 seconds; Effect Size [ES] = 1.59, p < 0.001). Speed (30-m sprint) was improved by T2 (4.46 ± 0.22 seconds vs. 4.30 ± 0.19 seconds; ES = 0.81, p < 0.001) and T3 (4.48 ± 0.22 seconds vs. 4.35 ± 0.21 seconds; ES = 0.58, p < 0.001). Agility (T-test) was improved by T1 (10.14 ± 0.40 seconds vs. 9.84 ± 0.42 seconds; ES = 0.73, p < 0.05) and T3 (9.93 ± 0.38 seconds vs. 9.66 ± 0.45 seconds; ES = 0.66, p < 0.001). Endurance (Yo-Yo level 1) was improved by T1 (1,682.22 ± 497.23 m vs. 2,028.89 ± 604.74 m; ES = 0.63, p < 0.05), T2 (1,904.35 ± 526.77 m vs. 2,299.13 ± 606.97 m; ES = 0.69, p < 0.001), and T3 (1,851.76 ± 490.46 m vs. 2,024.35 ± 588.13 m; ES = 0.35, p < 0.05). Power (countermovement jump) was improved by T3 only (36.01 ± 5.73 cm vs. 37.14 ± 5.62 cm; ES = 0.20, p < 0.05). There were no differences in T1, T2, and T3 combined when comparing PG and EG. The PG reported significantly (χ(20) = 4.42, p = 0.035, ES = 0.48) better training responses to T3 for power than the EG. These results demonstrate the efficacy of SSGs and SSTs in developing biomotor abilities. Although these results refute talent identification through the use of a TGS, there may be use in aligning the training method to TGS to develop power-based qualities in soccer.

#7 To Measure Peak Velocity in Soccer, Let the Players Sprint
Reference: J Strength Cond Res. 2019 Nov 27. doi: 10.1519/JSC.0000000000003406. [Epub ahead of print]
Authors: Kyprianou E, Di Salvo V, Lolli L, Al Haddad H, Villanueva AM, Gregson W, Weston M
Summary: Expressing externals loads relative to a player's individual capacities has potential to enhance understanding of dose-response. Peak velocity is an important metric for the individualization process and is usually measured during a sprint test. Recently, however, peak velocity was reported to be faster during soccer matches when compared with a 40-m sprint test. With the aim of developing the practice of individualized training prescription and match evaluation, we examined whether the aforementioned finding replicates in a group of elite youth soccer players across a broader range of soccer activities. To do this, we compared the peak velocities of 12 full-time male youth soccer players (age 16.3 ± 0.8 years) recorded during a 40-m sprint test with peak velocity recorded during their routine activities (matches, sprints, and skill-based conditioning drills: small-sided games [SSG], medium-sided games [MSG], large-sided games [LSG]). All activities were monitored with 10-Hz global positioning systems (Catapult Optimeye S5, version 7.32) with the highest speed attained during each activity retained as the instantaneous peak velocity. Interpretation of clear between-activity differences in peak velocity was based on nonoverlap of the 95% confidence intervals for the mean difference between activities with sprint testing. Peak velocity was clearly faster for the sprint test (8.76 ± 0.39 m·s) when compared with matches (7.94 ± 0.49 m·s), LSG (6.94 ± 0.65 m·s), MSG (6.40 ± 0.75 m·s), and SSG (5.25 ± 0.92 m·s), but not sprints (8.50 ± 0.36 m·s). Our data show the necessity for 40-m sprint testing to determine peak velocity.

#8 Contribution of Eccentric Strength to Cutting Performance in Female Soccer Players
Reference: J Strength Cond Res. 2019 Nov 28. doi: 10.1519/JSC.0000000000003433. [Epub ahead of print]
Authors: Jones PA, Dos'Santos T, McMahon JJ, Graham-Smith P
Summary: The aim of this study was to examine the contribution of eccentric strength to performance of a 70-90° cutting task (CUT) (time to complete: 5 m approach, 70-90° cut, 3 m exit). Nineteen female soccer players (mean ± SD age, height, and mass; 21.7 ± 4.3 years, 1.67 ± 0.07 m, and 60.5 ± 6.1 kg) from the top 2 tiers of English women's soccer participated in the study. Each player performed 6 trials of the CUT task whereby three-dimensional motion data from 10 Qualisys proreflex cameras (240 Hz) and ground reaction forces from 2 Advanced Mechanical Technology, Inc. force platforms (1,200 Hz) were collected. Relative eccentric knee extensor (ECC-KE) and flexor peak moments (ECC-KF) were collected from both limbs at 60°·s using a Kin-Com isokinetic dynamometer. Hierarchical multiple regression revealed that minimum center of mass (CM) and approach velocities (CM velocity at touchdown of penultimate foot contact) could explain 82% (79% adjusted) of the variation in CUT completion time (F(1,16) = 36.086, p < 0.0001). ECC-KE was significantly (p < 0.05) moderately associated (R ≥ 0.610) with velocities at key instances during the CUT. High (upper 50th percentile) ECC-KE individuals (n = 9) had significantly (p ≤ 0.01; d ≥ 1.34) greater velocities at key instances during the CUT. The findings suggest that individuals with higher ECC-KE produce faster CUT performance, by approaching with greater velocity and maintaining a higher velocity during penultimate and final contact, as they are better able to tolerate the larger loads associated with a faster approach.

#9 Epidemiology of Anterior Cruciate Ligament Injury in Italian First Division Soccer Players
Reference: Sports Health. 2019 Dec 4:1941738119885642. doi: 10.1177/1941738119885642. [Epub ahead of print]
Authors: Grassi A, Macchiarola L, Filippini M, Lucidi GA, Della Villa F, Zaffagnini S
Summary: The burden of anterior cruciate ligament (ACL) injury in professional soccer players is particularly relevant as it represents a potentially career-threatening injury. Our hypotheses were that (1) injury incidence rate would be similar to that reported in the literature, (2) we would identify a uniform distribution of the injuries along the season, and (3) injury incidence rate would be similar in high-ranked and lower ranked teams, based on final placement in the league. Professional male soccer players participating in the Serie A championship league in 7 consecutive seasons (2011-2012 to 2017-2018) were screened to identify ACL injuries through the online football archive . Exposure in matches and training were calculated. There were 84 ACL injuries found (mean player age, 25.3 ± 4.2 years). Overall, 25% of ACL injuries were reruptures (15%) or contralateral injuries (10%). ACL incidence rate was 0.4215 per 1000 hours of play during Serie A matches, 0.0305 per 1000 hours of training (rate ratio [RR], 13.8; 95% CI, 8.4-22.7; P < 0.0001), and 0.0618 per 1000 hours of total play. Injury distribution had a bimodal peak, with the highest number of events in October and March. Alternatively, training injuries peaked in June and July. A significantly higher incidence rate was found for the teams ranked from 1st to the 4th place compared with those ranked 5th to 20th (0.1256 vs 0.0559 per 1000 hours of play; RR, 2.2; 95% CI, 1.4-3.6; P = 0.0003). A similar finding was found for injury incidence proportion (3.76% vs 1.64%; P = 0.0003). The overall incidence rate of ACL injuries in Italian Serie A was 0.062 per 1000 hours, with a 14-fold risk in matches compared with training. Relevantly, 25% were second injuries. Most injuries occurred in October and March, and an almost 2-fold incidence rate and incidence proportion were noted in those teams ranked in the first 4 positions of the championship league. Knowing the precise epidemiology of ACL injury in one of the most competitive professional football championship leagues could help delineate fields of research aimed to investigate its risk factors.

#10 Factors Associated With Knee Pain and Heel Pain in Youth Soccer Players Aged 8 to 12 Years
Reference: Orthop J Sports Med. 2019 Nov 20;7(11):2325967119883370. doi: 10.1177/2325967119883370. eCollection 2019 Nov.
Authors: Iwame T, Matsuura T, Suzue N, Iwase J, Uemura H, Sairyo K
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Summary: Soccer is played by many children younger than 12 years. Despite its health benefits, soccer has also been linked to a high number of sport-related injuries. The purpose was to investigate the relationship between clinical factors and knee or heel pain in youth soccer players. Study participants included 602 soccer players aged 8 to 12 years who were asked whether they had experienced episodes of knee or heel pain. Data were collected on age, body mass index, years of playing soccer, playing position, and training hours per week. Associations of clinical factors with the prevalence of knee or heel pain were examined by univariate and multivariate logistic regression analyses. Episodes of knee and heel pain were reported by 29.4% and 31.1% of players, respectively. Multivariate analyses revealed that older age and more years of playing soccer were significantly and positively associated with the prevalence of knee pain (P = .037 and P = .015 for trend, respectively) but did not identify any significant associations for heel pain. In this study of youth soccer players, knee pain was associated with older age and more years of play, but heel pain was not significantly associated with any factor.

#11 Intra- and Post-match Time-Course of Indicators Related to Perceived and Performance Fatigability and Recovery in Elite Youth Soccer Players
Reference: Front Physiol. 2019 Nov 15;10:1383. doi: 10.3389/fphys.2019.01383. eCollection 2019.
Authors: Kunz P, Zinner C, Holmberg HC, Sperlich B
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Summary: Our aims were to examine (i) the internal load during simulated soccer match-play by elite youth players; and (ii) the time-course of subsequent recovery from perceived and performance fatigability. Eleven male youth players (16 ± 1 years, 178 ± 7 cm, 67 ± 7 kg) participated in a 2 × 40-min simulated soccer match, completing 30 rounds (160 s each) with every round including multidirectional and linear sprinting (LS20m), jumping (CMJ) and running at different intensities. During each round, LS20m, CMJ, agility, heart rate (HR), oxygen uptake (VO2), energy expenditure (EE), substrate utilization and perceived exertion RPE were assessed. In addition, the blood level of lactate (Lac) was obtained after each of the five rounds. Creatine kinase (CK) concentration, maximal voluntary isometric knee extension and flexion, CMJ, number of skippings in 30 s, and subjective ratings on the Acute Recovery and Stress Scale (ARSS) were examined before and immediately, 24 and 48 h after the simulation. During the game %HRpeak (p < 0.05, d = 1.08), %VO2 peak (p < 0.05; d = 0.68), Lac (p < 0.05, d = 2.59), RPEtotal (p < 0.05, d = 4.59), and RPElegs (p < 0.05, d = 4.45) all increased with time during both halves (all p < 0.05). Agility improved (p < 0.05, d = 0.70) over the time-course of the game, with no changes in LS20m (p ≥ 0.05, d = 0.34) or CMJ (p ≥ 0.05, d = 0.27). EE was similar during both halves (528 ± 58 vs. 514 ± 61 kcal; p = 0.60; d = 0.23), with 62% (second half: 65%) carbohydrate, 9% (9%) protein and 26% (27%) fat utilization. With respect to recovery, maximal voluntary knee extension (p ≥ 0.05, d = 0.50) and flexion force (p ≥ 0.05, d = 0.19), CMJ (p ≥ 0.05, d = 0.13), number of ground contacts (p ≥ 0.05, d = 0.57) and average contact time (p ≥ 0.05, d = 0.39) during 30-s of skipping remained unaltered 24 and 48 h after the game. Most ARSS dimensions of load (p < 0.05, d = 3.79) and recovery (p < 0.05, d = 3.22) returned to baseline levels after 24 h of recovery. Relative to baseline values, CK was elevated immediately and 24 h after (p < 0.05, d = 2.03) and normalized 48 h later. In youth soccer players the simulated match evoked considerable circulatory, metabolic and perceptual load, with an EE of 1042 ± 118 kcal. Among the indicators of perceived and performance fatigability examined, the level of CK and certain subjective ratings differed considerably immediately following or 24-48 h after a 2 × 40-min simulated soccer match in comparison to baseline. Accordingly, monitoring these variables may assist coaches in assessing a U17 player's perceived and performance fatigability in connection with scheduling training following a soccer match.

#12 Injury Incidence and Workloads during congested Schedules in Football
Reference: Int J Sports Med. 2019 Dec 2. doi: 10.1055/a-1028-7600. [Epub ahead of print]
Authors: Howle K, Waterson A, Duffield R
Summary: This study compared injury incidence and training loads between single and multi-match weeks, and seasons with and without congested scheduling. Measures of internal (session-Rating of Perceived Exertion × duration for training/match and % maximal heart rate) and external load (total, low-, high-, and very high-intensity running distances) along with injury incidence rates were determined from 42 players over 3 seasons; including 1 without and 2 (season 2 and 3) with regular multi-match weeks. Within-player analyses compared 1 (n=214) vs. 2-match (n=86) weeks (>75min in matches), whilst team data was compared between seasons. Total injury rates were increased during multi-match weeks (p=0.001), resulting from increased match and training injuries (50.3, 16.9/1000h). Between-season total injury rates were highest when congested scheduling was greatest in season 3 (27.3/1000h) and season 2 (22.7/1000h) vs. season 1 (14.1/1000h; p=0.021). All external load measures were reduced in multi-match weeks (p<0.05). Furthermore, all internal and external training loads were lowest in seasons with congestion (p<0.05). In conclusion, increased injury rates in training and matches exist. Total loads remain comparable between single and multi-match weeks, though reduce in congested seasons. Whether injuries result from reduced recovery, increased match exposure or the discreet match external loads remain to be elucidated.





Latest research in football - week 50 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Analysis of Physical Demands during Youth Soccer Match-play: Considerations of Sampling Method and Epoch Length
Reference: Res Q Exerc Sport. 2019 Nov 27:1-9. doi: 10.1080/02701367.2019.1669766. [Epub ahead of print]
Authors: Doncaster G, Page R, White P, Svenson R, Twist C
Summary: The purpose of this study was to examine the physical match profiles of professional soccer players using 3 and 5 min fixed and rolling averages as well as fixed 1 min averages, with considerations to training prescription. Twenty-nine professional U23 soccer outfield players competed across 17 competitive matches during the 2017/18 season, equating to a total of 130 separate physical match profiles. Match activities were recorded using global positioning system (GPS) devices with integrated micro-electrical mechanical systems (MEMS), recording total distance (TD), high-speed running (HSR), and metabolic power (MP). For each individual match profile and variable, 1, 3, and 5 min peak, post-peak, and average values were calculated using fixed-time epochs (FIXED) and rolling averages (ROLL). Linear mixed models were employed to examine the differences in the dependent variables as a function of the method of measurement. Results revealed significantly higher peak values, for relative TD, relative HSR and relative MP when employing the ROLL sampling method, in comparison to the FIXED method, for both 3 min and 5 min epoch lengths. Analysis of epoch length revealed significantly higher peak values, across all positions, for relative TD, relative HSR and MP for 1 min epochs, in comparison to 3 min and 5 min epochs. The data offers a novel insight into the appropriate identification of physical demands during youth soccer match-play. Researchers and practitioners should consider the sampling method and epoch length when assessing the physical demands of competitive match-play, as well as when designing and prescribing sport-specific conditioning drills.

#2 Maturity offset affects standing postural control in youth male soccer players
Reference: J Biomech. 2019 Nov 18:109523. doi: 10.1016/j.jbiomech.2019.109523. [Epub ahead of print]
Authors: Zago M, Moorhead AP, Bertozzi F, Sforza C, Tarabini M, Galli M
Summary: Quantifying the response of postural control in developmental athletes makes it possible to understand critical coordination and learning phases and to improve technical-physical interventions. However, the influence of maturation on postural control amongst young soccer players has neither been tested using quantitative methods, nor over a wide age range. In this study, we examined stabilometric parameters of 238 young male soccer players from 9 to 17 years old relative to maturity offset. Two 30-s tests (eyes open and eyes closed) were recorded on a baropodometric platform at 50 Hz. Participants were split into six groups according to their maturity offset, expressed as years from individual's peak height velocity. Dependent variables were: Sway Area, Center-of-Pressure velocity, standard deviation of the antero-posterior and medio-lateral Center-of-Pressure trajectory, Romberg Quotient. Sway Area was significantly higher in players with maturity offset <-1.5 than in groups with maturity offset > 0.5 years (p < 0.001, large effect). Center-of-Pressure velocity markedly dropped in players with maturity offset >-0.5 years (p < 0.001, very large effect). Antero-posterior standard deviation was higher before than after peak height velocity (p < 0.05, large effect) and significantly higher with closed eyes at some points. Medio-lateral standard deviation was higher in the youngest group of players (maturity offset <-2.5 years, large effect) than in those with maturity offset >-0.5 years. In sum, stabilometric parameters improved with age until zero maturity offset was achieved. Thereafter, variables describing postural control in developing soccer players were almost stable. No evidence of a changing role of vision in postural sway control during maturation was observed.

#3 Effect of pre-season training phase on anthropometric, hormonal and fitness parameters in young soccer players
Reference: PLoS One. 2019 Nov 25;14(11):e0225471. doi: 10.1371/journal.pone.0225471. eCollection 2019.
Authors: Perroni F, Fittipaldi S, Falcioni L, Ghizzoni L, Borrione P, Vetrano M, Del Vescovo R, Migliaccio S, Guidetti L, Baldari C
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Summary: The aims of the study were to investigate 1) the effect of 8 weeks of PSP training on anthropometrics, salivary hormones and fitness parameters in youth soccer players, 2) the correlations between fitness and hormonal parameters, and 3) the impact of the experience of the coach and his methodology of training on these parameters. Weight, height, BMI, pubertal development (PDS), salivary Cortisol (sC), salivary Testosterone (sT), salivary sDHEAS, intermittent tests (VO2max), and countermovement jump test (CMJ) modifications of 35 youth soccer players (age: 14±0 yrs; BMI: 20.8±1.8 k/m2) from two Italian clubs ("Lupa Frascati" -LF-; "Albalonga" -AL) were analysed. A significant (p<0.05) time by club effect was observed in sC (F(1,31) = 9.7, ES = 1.13), sT (F(1,31) = 4.2, ES = 0.74), CMJ (F(1,28) = 26.5, ES = 1.94), and VO2max (F(1,28) = 8.5, ES = 1.10). Statistical differences (p<0.05) in weight (F(1,32) = 25.5, ES = 0.11), sC (F(1,31) = 32.1, ES = 1.43), sT/sC ratio (F(1,31) = 10.1, ES = 0.97), sDHEAS/sC ratio (F(1,31) = 6.3, ES = 0.70), and VO2max (F(1,28) = 64.3, ES = 1.74) were found within time factor. Between clubs, differences (p<0.05) in sC (F(1,32) = 8.5, ES = 1.17), sT (F(1,31) = 4.2, ES = 0.74), CMJ (F(1,28) = 26.5, ES = 1.50), and VO2max (F(1,28) = 8.5, ES = 1.10) were found. CMJ was inversely correlated with sDHEAS (r = -0.38) before PSP, while Δ of CMJ showed significant correlations with Δ of sC (r = 0.43) and ΔVO2max was inversely correlated with ΔBMI (r = -0.54) and ΔsC (r = -0.37) in all subjects. Considering each single club, ΔVO2max showed correlations with ΔBMI (r = -0.45) in AL, while ΔCMJ showed correlations with ΔPDS (r = 0.72) in LF club. Since the PSP is often limited training time to simultaneously develop physical, technical and tactical qualities, an efficient method to distribute the training load is important in youth soccer players to increase the performance and to avoid injuries.

#4 Relationship Between Repeated Sprint Ability, Aerobic Capacity, Intermittent Endurance, and Heart Rate Recovery in Youth Soccer Players
Reference: J Strength Cond Res. 2019 Dec;33(12):3406-3413. doi: 10.1519/JSC.0000000000002193.
Authors: Rodríguez-Fernández A, Sanchez-Sanchez J, Ramirez-Campillo R, Nakamura FY, Rodríguez-Marroyo JA, Villa-Vicente JG
Summary: The purpose was to investigate the relationship between repeated sprint ability (RSA) and several aerobic and anaerobic-related soccer-performance indicators, 45 youth soccer players (age 16.8 ± 0.1 years) were classified into "high" (HAF) or "low" aerobic fitness (LAF) (VO2max ≥ or <60 ml·kg·min, respectively) and completed an RSA test measuring best (RSAbest), mean (RSAmean), total sprint time (RSAtotal), and percent sprint decrement (Sdec). A laboratory VO2max test (LabTest) together with anaerobic threshold (VT) and peak speed was measured (vLabTest). In addition, a 20-m multistage shuttle run test (MSRT) and a soccer-specific test (TIVRE-Soccer test-TST) were completed. Heart rate (HR) and HR recovery (HRR) were measured during all tests. High aerobic fitness presented greater (p ≤ 0.05) performance in LabTest, MSRT and TST, at maximal effort, at VT, as well as faster HRR. RSA was similar between HAF and LAF. Contrary to HAF, LAF showed negative correlation between vLabTest with RSAmean (r = -0.6, p = 0.000) and Sdec (r = -0.4, p = 0.044). Also, LAF showed negative correlation between TST end speed (vTST) and RSAmean (r = -0.5, p = 0.005) and Sdec (r = -0.5, p = 0.003). In LAF, RSA was strongly correlated with locomotor factors (e.g., vTST; VT) in both laboratory and field tests. Athletes with high total HRR (>12.5%) in TST presented better (p ≤ 0.05) Sdec in the RSA test. The multiple regression revealed that the LAF vLabTest explained 44.9, 40.0, and 13.5% of the variance in RSAbest, RSAmean, and Sdec, respectively. Practitioners may consider these findings to optimize youth athletes' assessment and preparation processes.

#5 Workload efficiency as a new tool to describe external and internal competitive match load of a professional soccer team: A descriptive study on the relationship between pre-game training loads and relative match load
Reference: Eur J Sport Sci. 2019 Nov 25:1-17. doi: 10.1080/17461391.2019.1697374. [Epub ahead of print]
Authors: Grünbichler J, Federolf P, Gatterer H
Summary: The current study introduces a new index for external and internal workload, "workload efficiency", and assesses in professional soccer the influence of pre-match training load on match workload efficiency. External and internal workloads were determined for 44 training sessions and 16 competitive matches using a 10-Hz global positioning system (GPS) and a 200-Hz accelerometer/heart rate monitor. Training loads were registered from day five (D-5) to day one (D-1) prior to each competitive match. Workload efficiency was calculated for each match as the ratio between overall external and internal load. A multiple stepwise regression analysis (including z-transformed variables) was used to determine training load variables that predict workload efficiency of the following matches. Training load variables of the previous days explained 26.6% of the variance in workload efficiency during the following matches. Long sprinting distance on D-3 and D-4 and total distance on D-1 positively influenced the players' workload efficiency, whereas long training durations and high training load on D-1 showed adverse effects. The present outcomes suggest that including sprint training (high sprinting distance) four and three days prior to a match, may provide a positive stimulus for the subsequent workload efficiency in matches. The negative impact of long training duration and high training load one day before the game highlights the importance of a diligent planning of the immediate competition preparation phase. This study shows that workload efficiency is a useful metric to assess match performance and that body-worn sensor technology can be useful for tailoring training loads.

#6 Contribution of lower body segment rotations in various height soccer volley kicking
Reference: Sports Biomech. 2019 Nov 25:1-16. doi: 10.1080/14763141.2019.1667422. [Epub ahead of print]
Authors: Sugi S, Nunome H, Tamura Y, Iga T, Lake M
Summary: We aimed to quantify the contribution of lower body segment rotations in producing foot velocity during the soccer volley kick. Fifteen male experienced university players kicked a soccer ball placed at four height conditions (0, 25, 50 and 75 cm). Their kicking motion was captured at 500 Hz. The effectiveness of lower body segment rotations in producing forward (Ffv) and upward (Fuv) foot velocity were computed and time integrated. Major contributors for Ffv were a) left hip linear velocity, b) knee extension and c) pelvis retroflexion (the pitch rotation). The contribution of a) become smaller as the ball height increased while those of b) and c) did not change significantly. Moreover, the pelvis clockwise rotation (the yaw rotation) showed apparent contribution only for volley kicking (except 0 cm height). Major contributors for Fuv were 1) knee flexion, 2) hip internal rotation, 3) pelvis clockwise rotation (the roll rotation) and 4) hip flexion. The contributions of 1) and 4) become consistently smaller as the ball height increased, while those of 2) and 3) become larger systematically. Soccer volley kicking was found to have unique adaptations of segmental contributions to achieve higher foot position while maintain foot forward velocity.

#8 Physical capacity, not skeletal maturity, distinguishes competitive levels in male Norwegian U14 soccer players
Reference: Scand J Med Sci Sports. 2019 Oct 12. doi: 10.1111/sms.13572. [Epub ahead of print]
Authors: Grendstad H, Nilsen AK, Rygh CB, Hafstad A, Kristoffersen M, Iversen VV, Nybakken T, Vestbøstad M, Algrøy EA, Sandbakk Ø, Gundersen H
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Summary: The main aim of the present study was to compare skeletal maturity level and physical capacities between male Norwegian soccer players playing at elite, sub-elite and non-elite level. Secondary, we aimed to investigate the association between skeletal maturity level and physical capacities. One hundred and two U14 soccer players (12.8-14.5 years old) recruited from four local clubs, and a regional team were tested for bone age and physical capacities. Bone age was estimated with x-ray of their left hand and used to indicate maturation of the skeleton. Players went through a comprehensive test battery to assess their physical capacities. Between-groups analysis revealed no difference in chronological age, skeletal maturity level, leg strength, body weight, or stature. However, elite players were superior to sub-elite and non-elite players on important functional characteristics as intermittent-endurance capacity (running distance: 1664 m ± 367 vs 1197 m ± 338 vs 693 m ± 235) and running speed (fastest 10 m split time: 1.27 seconds ± 0.06 vs 1.33 seconds ± 0.10 vs 1.39 seconds ± 0.11), in addition to maximal oxygen uptake ( VO2max ), standing long jump, and upper body strength (P < .05 for all comparisons). Medium-to-large correlations were found between skeletal maturity level and peak force (r = 695, P < .01), power (r = 684, P < .01), sprint (r = -.471, P<.001), and jump performance (r = .359, P < .01), but no correlation with upper body strength, VO2max , or intermittent-endurance capacity. These findings imply that skeletal maturity level does not bias the selection of players, although well-developed physical capacity clearly distinguishes competitive levels. The superior physical performance of the highest-ranked players seems related to an appropriate training environment.

#9 Incidence of injuries among professional football players in Spain during three consecutive seasons: A longitudinal, retrospective study
Reference: Phys Ther Sport. 2019 Nov 19;41:87-93. doi: 10.1016/j.ptsp.2019.11.008. [Epub ahead of print]
Authors: Torrontegui-Duarte M, Gijon-Nogueron G, Perez-Frias JC, Morales-Asencio JM, Luque-Suarez A
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Summary: The aim of the study was to determine risk factors that maybe be associated with a higher incidence of injuries in elite football players in the Spanish league during a three-year follow-up. Injury was defined as a musculoskeletal complaint (pain and/or discomfort) reported by players to the medical staff and receiving medical attention.  Seventy-one players from Malaga Football Club, who were in the first squad team for three consecutive seasons participated in this study. Incidence, location, severity of injuries were reported according to the Injury Consensus Group for football injuries. Three hundred and fifty six injuries were found, with the highest proportion (44%) being located in the thigh. We found 6.9 (SD 5.87) injuries per 1000 h of match time and 0.23 (SD 0.22) per 1000 h of training. Forwards presented the highest rates in both incidence and severity of injury. Exposure to training was inversely related to the total number of injuries, which means that the greater the exposure to training the lesser the number of injuries. This information can assist clinicians in the identification of risk factors and, thus, the elaboration of prevention programmes that reduce football injuries.

#10 An Extensive Comparative Analysis of Successful and Unsuccessful Football Teams in LaLiga
Reference: Front Psychol. 2019 Nov 8;10:2566. doi: 10.3389/fpsyg.2019.02566. eCollection 2019.
Authors: Brito de Souza D, López-Del Campo R, Blanco-Pita H, Resta R, Del Coso J
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Summary: The characterization of the in-game actions with the strongest influence on victory in football might be useful for designing playing styles that enhance teams' performance. The aim of this study was to analyze in-game match statistics on the top-3 and bottom-3 teams ranked in LaLiga. Accumulated offensive and defensive match statistics when playing at home and away were obtained from LaLiga for 8 consecutive seasons. Data extraction was performed by computerized video-analysis. The top-3 and bottom-3 teams were compared using independent t-test analysis and the magnitude of the difference was cataloged with effect sizes. Overall, the offensive variable with the greatest magnitude of difference in the top-3 vs. bottom-3 comparison was shooting accuracy (ES ± 90% confidence interval = 4.15 ± 0.52) followed by the number of offsides (2.25 ± 0.60) and corners (2.14 ± 0.61). However, when playing away, the offensive variable with the greatest magnitude of difference in the top-3 vs bottom-3 comparison was the number of shots (3.30 ± 0.44). The defensive variables that best differentiated top 3 - bottom 3 teams were the number of corners (2.16 ± 0.43) and shots conceded (2.04 ± 0.39). In conclusion, the match statistics that best discriminated successful from unsuccessful football teams were shooting accuracy while attacking and the number of shots conceded while defending.

#11 Submaximal field testing validity for aerobic fitness assessment in recreational football
Reference: Scand J Med Sci Sports. 2019 Nov 27. doi: 10.1111/sms.13606. [Epub ahead of print]
Authors: Cristina Araújo Póvoas S, Krustrup P, Castagna C
Summary: Submaximal field tests are especially recommended when repeated testing is warranted. This study aimed at assessing the validity of the submaximal versions of the Yo-Yo intermittent tests in male recreational football players in untrained and trained status. The participants' (n=66; age 39.3±5.8 years, VO2max 41.2±6.2 ml·kg-1 ·min-1 , body mass 81.9±10.8 kg, height 173.2±6.4 cm) heart rate after 2 min (HR2min ) during the level 1 (YYIE1HR2min ) and 2 (YYIE2HR2min ) versions of the Yo-Yo intermittent endurance test and the level 1 version of the Yo-Yo intermittent recovery test (YYIRHR2min ) was plotted against individual VO2max values. Thirty-two participants performed all the tests after a 12-week recreational football intervention for test responsiveness. Associations between VO2max and YYIE1HR2min were large to small (P=0.0001). Large to trivial associations were found between YYIE2HR2min , YYIR1HR2min and VO2max (P<0.01). Maximal Yo-Yo performances were large, significant and inversely related to HR2min (-0.68 to -0.49, P<0.0001). Pre-to-post-intervention ICC values were good for YYIE1HR2min and YYIE2HR2min , and excellent for YYIR1HR2min . Post-intervention associations between HR2min and Yo-Yo maximal performances were large to very large (-0.55 to -0.72; P<0.002, n=32). Training-induced changes in VO2max moderately correlated with YYR1HR2min (-0.48; P=0.007; n=32). HR2min lower than 89%, 98% and 91%HRmax for YYIE1HR2min , YYIE2HR2min and YYIR1HR2min , respectively, may be considered as signs of good to excellent VO2max levels. Since in the YYIE1HR2min , the participants attained 84%HRmax and test specificity increased for HR2min values <89%, this test may be the preferred choice when repeated assessment of aerobic fitness, using submaximal intermittent Yo-Yo tests, is considered in recreational football.





Latest research in football - week 49 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Football as a Health Promotion Strategy
Reference: Dtsch Arztebl Int. 2019 Oct 25;116(43):721-728. doi: 10.3238/arztebl.2019.0721.
Authors: Eberl M1, Tanaka LF, Klug SJ, Adamek HE.
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Summary: Football training can be a primary prevention strategy to reach people who otherwise would not be physically active. This systematic review summarizes the evidence on the health effects of controlled recreational football training as an intervention in children, adolescents, adults and the elderly. A systematic review (PROSPERO record CRD42018083665) of the literature was carried out in MEDLINE, Cochrane, Scopus, and SPORTDiscus databases to identify randomized and non-randomized intervention studies in which healthy individuals of any age participated in controlled football training and were investigated for health outcomes related to prevention of obesity, hypertension, diabetes mellitus, and cardiovascular disease. The studies included-14 randomized and three non-randomized intervention studies-have sample sizes too small for reliable statistical analysis and bear a considerable risk of systematic bias. The evidence of positive effects of playing football is limited to short-term loss of body fat and improvement in aerobic fitness. For all other health outcomes, no conclusive results were found. A considerable number of intervention studies reporting on football-based intervention programs have been published, and there is a widespread assumption that such programs have positive health effects. However, this systematic review shows that the empirical evidence is insufficient to permit such a conclusion.

#2 Methods to collect and interpret external training load using microtechnology incorporating GPS in professional football: a systematic review
Reference: Res Sports Med. 2019 Nov 22:1-22. doi: 10.1080/15438627.2019.1686703. [Epub ahead of print]
Authors: Rago V, Brito J, Figueiredo P, Costa J, Barreira D, Krustrup P, Rebelo A
Summary: The aim of this article was to systematically review the methods adopted to collect and interpret external training load (ETL) using microtechnology incorporating global positioning system (GPS). The main deficiencies identified concerned the non-collection of match ETL, and the non-consideration of potential confounders (e.g. playing position, fitness level, starting status or session content). Also, complementary training (individual/reconditioning) and pre-match warm-up were rarely quantified. To provide a full picture of the training demands, ETL was commonly complemented by internal training load monitoring with the rating of perceived exertion predominantly adopted instead of heart rate recordings. Continuous data collection and interpretation of ETL data in professional football vary widely between observational studies, possibly reflecting the actual procedures adopted in practical settings. Evidence about continuous ETL monitoring in female players, and female as well as male goalkeepers is lacking.

#3 Psychological factors and future performance of football players: A systematic review with meta-analysis
Reference: J Sci Med Sport. 2019 Nov 1. pii: S1440-2440(19)30559-6. doi: 10.1016/j.jsams.2019.10.021. [Epub ahead of print]
Authors: Ivarsson A, Kilhage-Persson A, Martindale R, Priestley D, Huijgen B, Ardern C, McCall A
Summary: This systematic review had 3 key objectives: (1) to investigate whether psychological factors were associated with future football performance (e.g., progression to professional football, better game statistics during the next season); (2) to critically review the methodological approaches used in the included studies and summarize the evidence for the current research question; (3) to provide guidelines for future studies. Electronic databases (SPORTDiscus, PubMed and PsycINFO) and previously published systematic and scoping reviews were searched. Only prospective studies were considered for inclusion. Eleven published studies that reported 39 effect sizes were included. Psychological factors; task orientation, task-oriented coping strategies and perceptual-cognitive functions had small effects on future performance in football (ds=0.20-0.29). Due to high risk of bias there were low certainty of evidence for psychological factors relationship with future football performance. Psychological factors investigated showed small effects on future football performance, however, there was overall uncertainty in this evidence due to various sources of bias in the included studies. Therefore psychological factors cannot be used as a sole deciding factor in player recruitment, retention, release strategies, however it would appear appropriate to include these in the overall decision-making process. Future, studies with more appropriate and robust research designs are urgently needed to provide more certainty around their actual role.

#4 Physical preparation and return to sport of the football player with a tibia-fibula fracture: applying the 'control-chaos continuum'
Reference: BMJ Open Sport Exerc Med. 2019 Oct 30;5(1):e000639. doi: 10.1136/bmjsem-2019-000639. eCollection 2019.
Authors: Taberner M, van Dyk N, Allen T, Richter C, Howarth C, Scott S, Cohen DD
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Summary: Contact in elite football can result in severe injury such as traumatic fracture. Limited information exists regarding the rehabilitation and return to sport (RTS) of these injuries especially in elite football. We outline the RTS of an elite English Premier League footballer following a tibia-fibula fracture including gym-based physical preparation and the use of 'control-chaos continuum' as a framework for on-pitch sport-specific conditioning, development of technical skills while returning the player to pre-injury chronic running loads considering the qualitative nature of movement in competition. Strength and power diagnostics were used to back up clinical reasoning and decision-making throughout rehabilitation and the RTS process. The player returned to full team training after 7.5 months, completed 90 min match-play after 9 months and remains injury-free 11 months post-RTS.

#5 The Attacking Process in Football: A Taxonomy for Classifying How Teams Create Goal Scoring Opportunities Using a Case Study of Crystal Palace FC
Reference: Front Psychol. 2019 Oct 16;10:2202. doi: 10.3389/fpsyg.2019.02202. eCollection 2019.
Authors: Kim J, James N, Parmar N, Ali B, Vučković G
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Summary: Whilst some studies have comprehensively described the different features associated with the attacking process in football they have not produced a methodology of practical use for performance enhancement. This study presents a framework of comprehensive and meaningful metrics to objectively describe the attacking process so that useful performance profiles can be produced. The attacking process was categorized into three independent situations, no advantage (stable), advantage, and unstable (potential goal scoring opportunity) situations. Operational definitions for each situation enhanced their reliability and validity. English Premier League football matches (n = 38) played by Crystal Palace Football Club in the 2017/2018 season were analyzed as an exemplar. Crystal Palace FC created a median of 53.5 advantage situations (IQR = 16.8) and 23 unstable situations (IQR = 8.8) per match. They frequently utilized wide areas (Median = 21.5, IQR = 9.8) to progress, but only 26.6% resulted in unstable situations (Median = 6.0, IQR = 3.8), the lowest rate compared to the other advantage situations. This classification framework, when used with contextual factors in a multi-factorial manner, including individual player contributions, will provide practically useful information for applied practice. This approach will help close the so called theory-practice gap and enable academic rigor to inform practical problems.

#6 Recovery Kinetics After Speed-Endurance Training in Male Soccer Players
Reference: Int J Sports Physiol Perform. 2019 Nov 21:1-14. doi: 10.1123/ijspp.2018-0984. [Epub ahead of print]
Authors: Tzatzakis T, Papanikolaou K, Draganidis D, Tsimeas P, Kritikos S, Poulios A, Laschou VC, Deli CK, Chatzinikolaou A, Batrakoulis A, Basdekis G, Mohr M, Krustrup P, Jamurtas AZ, Fatouros IG.
Summary: The purpose was to determine the recovery kinetics of performance, muscle damage, and neuromuscular fatigue following 2 speed-endurance production training (SEPT) protocols in soccer. Ten well-trained, male soccer athletes randomly completed 3 trials: work-to-rest ratio (SEPT) 1:5, SEPT/1:8, and a control trial. Training load during SEPT was monitored using global positioning system and heart-rate monitors. Performance (isokinetic strength of knee extensors and flexors, speed, and countermovement jump) and muscle damage (delayed-onset muscle soreness [DOMS] and creatine kinase) were evaluated at baseline and at 0, 24, 48 and 72 h posttraining. Maximal voluntary contraction (fatigue index) of knee extensors and flexors was additionally assessed at 1, 2, and 3 h posttraining. Fatigue increased (P < .05) in SEPT/1:5 (∼4-30%) for 3 h and in SEPT/1:8 (∼8-17%) for 2 h. Strength performance declined (P < .05) in both SEPT trials (∼5-20%) for 48 h. Speed decreased (∼4-18%; P < .05) for 72 h in SEPT/1:5 and for 48 h in SEPT/1:8. Countermovement-jump performance decreased (∼7-12%; P < .05) in both SEPT trials for 24 h. DOMS increased (P < .05) in SEPT/1:5 (∼2-fold) for 72 and in SEPT/1:8 (∼1- to 2-fold) for 48 h. Creatine kinase increased (∼1- to 2-fold, P < .05) in both SEPT trials for 72 h. SEPT induces short-term neuromuscular fatigue; provokes a prolonged deterioration of strength (48 h), speed (72 h), and jump performance (24 h); and is associated with a prolonged (72-h) rise of DOMS and creatine kinase. Time for recovery is reduced when longer work-to-rest ratios are applied. Fitness status may affect quality of SEPT and recovery kinetics.

#7 Effect of opposition quality and match location on the positional demands of the 4-2-3-1 formation in elite soccer
Reference: J Exerc Sci Fit. 2020 Jan;18(1):40-45. doi: 10.1016/j.jesf.2019.11.001. Epub 2019 Nov 3.
Authors: Paraskevas G, Smilios I, Hadjicharalambous M
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Summary: The present study examined the influence of match location, quality of opposition team, and playing position on physical performance indicators of the 4-2-3-1 formation. Twenty-six (n = 26) games (with 184 player-observations; n = 17 players, played full 90 min games) were recorded with a video system and the physical demands of the players were analyzed according to their specific playing position (classified into central and wide defenders, central and wide midfielders and forwards). Match performance variables analyzed included total distance (TD), high-intensity running (HIR), very-high-intensity running (VHIR) and sprinting (SPR). There was a main effect of position for TD (F = 37.84, p < 0.001), HIR (F = 41.19, p < 0.001), VHIR (F = 27.89, p < 0.001) and SPR (F = 22.25, p < 0.001). Wide defenders covered the most SPR and -along with the central midfielders-the most VHIR. Central midfielders covered the most TD and HIR. Match location and opposition quality had interactive effects on TD (F = 12.96, p < 0.001), HIR (F = 8.33 p = 0.004) and VHIR (F = 8.17 p = 0.005). Competing against "weak" opponents, more TD, HIR and VHIR covered during home games compared to away games (p < 0.05). However, more TD was covered during away games against "strong" opponents compared to away games against "weak" opponents (p < 0.05). The current study supports more intense-based drills (i.e. repeated sprint training) for wide defenders and more volume-based drills (i.e. long interval training) for central midfielders, whilst total weekly training load can be adjusted based on match location and quality of oppositions on the anticipated game-load.

#8 Effects of Two Competitive Soccer Matches on Landing Biomechanics in Female Division I Soccer Players
Reference: Sports (Basel). 2019 Nov 14;7(11). pii: E237. doi: 10.3390/sports7110237.
Authors: Snyder BJ, Hutchison RE, Mills CJ, Parsons SJ
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Summary: Fatigue has been proposed to increase the risk of knee injury. This study tracked countermovement jump, knee isometric strength, and kinetics and kinematics in 8 female soccer players (experimental group) during an anticipated sidestep maneuver before and after two matches played over a 43-h period. Time points were: Before and after match 1 (T0 and T1), 12 h after the first match (T2), and immediately after the second match (T3). A control group participated only in practice sessions. Isometric knee extension strength decreased by 14.8% at T2 (p = 0.003), but knee flexion was not affected until T3, declining by 12.6% (p = 0.018). During the sidestep maneuver, knee joint degrees of flexion at initial contact was increased by 17.1% at T3, but maximum knee and hip angle at initial contact were unchanged. Peak resultant ground reaction force (GRF) increased by 12.6% (p = 0.047) at T3 (3.03 xBW) from 2.69 xBW at T0, while posterior GRF was significantly higher than T0 at all three subsequent time points (T1 = 0.82 ± 0.23 xBW, T2 = 0.87 ± 0.22 xBW, T3 = 0.89 ± 0.22 xBW). Anterior tibial shear force increased significantly (p = 0.020) at T3 (1.24 ± 0.12 xBW) compared to T1 (1.15 ± 0.13 xBW), an 8.8% increase. Lateral tibial shear force was significantly higher at both T1 (0.95 ± 0.20 xBW) and T3 (1.15 ± 0.38 xBW) compared to T0 (0.67 ± 0.25 xBW). These findings suggest that participation in a soccer match has significant effects on both physical performance parameters and kinetics/kinematics during a sidestep cut, but these can be more pronounced after a second match with short rest.

#9 Higher neck strength is associated with lower head acceleration during purposeful heading in soccer: A systematic review
Reference: J Sci Med Sport. 2019 Nov 12. pii: S1440-2440(19)30660-7. doi: 10.1016/j.jsams.2019.11.004. [Epub ahead of print]
Authors: Peek K, Elliott JM, Orr R
Summary: The purpose was to systematically review the literature to investigate the potential relationship between neck strength and head acceleration during purposeful heading in soccer. Comprehensive search of five electronic databases: EMBASE, MEDLINE, CINAHL, SportsDiscus and Web of Science. Studies were included if they reported data on the relationship between neck strength and head impact and/or acceleration during purposeful soccer heading, published in English (or translation available). From an initial search of 1174 potentially eligible papers, five cross-sectional studies met the eligibility criteria for inclusion in this review. Data from cross-sectional studies indicate that higher neck strength is associated with lower head acceleration during purposeful heading in soccer (p=<0.05; r<-0.5). This review provides evidence that higher neck strength may lower head acceleration during purposeful heading in soccer. Further research is required to determine the most effective method to strengthen the neck musculature in soccer players.

#10 Superior cardiac mechanics without structural adaptations in pre-adolescent soccer players
Reference: Eur J Prev Cardiol. 2019 Nov 28:2047487319890177. doi: 10.1177/2047487319890177. [Epub ahead of print]
Authors: Beaumont A, Oxborough D, George K, Rowland TW, Sculthorpe N, Lord R, Unnithan VB
Summary: This study aimed to evaluate left ventricular structure, function and mechanics, in highly-trained, pre-adolescent soccer players compared with age- and sex-matched controls. The study design was a prospective, cross-sectional comparison of left ventricular structure, function and mechanics. Twenty-two male soccer players from two professional youth soccer academies (age: 12.0 ± 0.3 years) and 22 recreationally active controls (age: 11.7 ± 0.3 years) were recruited. Two-dimensional conventional and speckle tracking echocardiography were used to quantify left ventricular structure, function and peak/temporal values for left ventricular strain and twist, respectively. End-diastolic volume index was larger in soccer players (51 ± 8 mm/(m2)1.5 vs. 45 ± 6 mm/(m2)1.5; p = 0.007) and concentricity was lower in soccer players (4.3 ± 0.7 g/(mL)0.667 vs. 4.9 ± 1.0 g/(mL)0.667; p = 0.017), without differences in mean wall thickness between groups (6.0 ± 0.4 mm vs. 6.1 ± 0.5 mm; p = 0.754). Peak circumferential strain at the base (-22.2% ± 2.5% vs. -20.5% ± 2.5%; p = 0.029) and papillary muscle levels (-20.1% ± 1.5% vs. -18.3% ± 2.5%; p = 0.007) were greater in soccer players. Peak left ventricular twist was larger in soccer players (16.92° ± 7.55° vs. 12.34° ± 4.99°; p = 0.035) and longitudinal early diastolic strain rate was greater in soccer players (2.22 ± 0.40 s-1 vs. 2.02 ± 0.46 s-1; p = 0.025). Highly-trained soccer players demonstrated augmented cardiac mechanics with greater circumferential strains, twist and faster diastolic lengthening in the absence of differences in wall thickness between soccer players and controls.

#11 The Role of Somatic Maturation on Bioimpedance Patterns and Body Composition in Male Elite Youth Soccer Players
Reference: Int J Environ Res Public Health. 2019 Nov 26;16(23). pii: E4711. doi: 10.3390/ijerph16234711.
Authors: Campa F, Silva AM, Iannuzzi V, Mascherini G, Benedetti L, Toselli S
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Summary: The purpose of this study was to examine the influence of chronological age (CA) and somatic maturation on body composition (BC) and bioimpedance parameters in male elite soccer players. BC and bioimpedance variables were measured in a sample of 249 players aged 9-18 years of age and registered in two professional Italian soccer teams. Results from segmental analysis showed transition time points where the influence of CA and somatic maturation on bioimpedance patterns and BC characteristics increased or subsided. The accelerated phases were assessed for fat free mass, total body water, and upper muscle area, with a starting time point at approximately -2.00 years from peak at velocity (YPHV), and for body cell mass, whose developmental tempo sped up around -1.00 YPHV. An increase in the rate of development was also observed close to -2.00 YPHV for phase angle (PA), although without accelerated phases. From a CA point of view, significant slope changes were found for all BC and bioimpendance variables, except for the calf muscle area. Although the starting points and the span of the accelerated phases were different, they subsided or disappeared at ~ 15 years, except for PA, whose growth waned at ~ 17 years.





Latest research in football - week 48 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Observational Studies in Male Elite Football: A Systematic Mixed Study Review
Reference: Front Psychol. 2019 Oct 18;10:2077. doi: 10.3389/fpsyg.2019.02077. eCollection 2019.
Authors: Preciado M, Anguera MT, Olarte M, Lapresa D
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Summary: This systematic mixed study review, focuses on the use of observation methodology in elite men's football matches, which constitutes an innovative approach, that opens up a new panorama of useful and productive research. The methods used in this study follow the recommendations for systematic reviews and meta-analysis guidelines (PRISMA). The search was carried out in five databases. Ninety-four articles out of 3,195 were selected and analyzed. In order to achieve a quality assessment, the guide was used to inform evaluations based on observation methodology (GREOM) (Portell et al., 2015), recognized by the EQUATOR network. From the methodological review analysis, information obtained indicates that 97% of the researches used direct observation and 3% indirect observation. On the other hand, 56.5% of the articles explain the instrument used and 77% justify the applied observational design. A quantitative comparison of the proportions was made in several methodological aspects, which resulted in only 15.21% reviewing the quality of the data, and that 67.3% of the articles contributed to the mixed methods approach. The methodological review allowed us to establish procedural profiles. The results indicate that 67% of the articles have been published in English, and of these, 77% were published in journals that have an impact factor. The majority of the researchers, 53.26%, belong to Spanish entities. The most studied substantive aspects were goal (34%), possession of the ball (28%), and corner (27%). The most observed events were Leagues, World Cups, individual players and other events. The results obtained refer to both substantive and methodological aspects and allow us to configure a systematic review of mixed studies, in which we emphasize the aspects of a "systematic review" and a "mixed study," within an integrated perspective.

#2 Hamstring injury prevention in Belgian and English elite football teams
Reference: Acta Orthop Belg. 2019 Sep;85(3):373-380.
Authors: Van Crombrugge G, Duvivier BM, Van Crombrugge K, Bellemans J, Peers K.
Summary: Hamstring injury is the most common injury in European professional football. The purpose of this study was to provide insight into the content of hamstring injury prevention programmes in English and Belgian elite football teams. Fifteen premier league teams (10 from Belgium and 5 from England) completed a questionnaire on hamstring injury prevention. Most football teams (93%) screened for hamstring injury risk factors. Less than 60% screened for risk factors including gluteus muscle strength, neural tension and body posture during running. While 80% of the teams had a hamstring injury prevention programme during preseason and official season ; only 47% had a prevention programme during mid-season break. Hamstring muscle strength exercises were mainly performed before (77%) instead of after warming-up. In conclusion, while most investigated football teams perform hamstring injury prevention, the content and implementation of the prevention programmes is suboptimal in many Belgian and English elite football teams.

#3 The Functional Movement Screen total score and physical performance in elite male collegiate soccer players
Reference: J Exerc Rehabil. 2019 Oct 28;15(5):657-662. doi: 10.12965/jer.1938422.211. eCollection 2019 Oct.
Authors: Lee S, Kim H, Kim J
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Summary: The objectives of this study were to compare the differences in physical performance of elite male collegiate soccer players according to the Functional Movement Screen (FMS) total scores and to investigate the association between the FMS total score and physical performance. A total of 20 elite male collegiate soccer players (mean age, 19.6±0.7 years; height, 173.4±4.4 cm; body weight, 66.9±7.3 kg; and body mass index, 22.0±2.0 kg/m2) participated in the present study. The subjects were divided into two groups: the high FMS (FMS total score ≥14 points, n=10) and low FMS (FMS total score <14 points, n=10). All participants completed 10-m and 30-m sprint tests, the arrowhead agility test (right and left), and a coordination test. The statistical methods used to verify the study results were the independent sample t-test and Kendall's Tau b correlation test. There were significant differences between the high and low FMS groups in the 10-m (P=0.014) and 30-m sprint (P=0.002) and arrowhead agility tests (right, P=0.039). Conversely, there were no significant differences in the arrowhead agility (left) and coordination tests between the two groups (P>0.05). Moreover, the FMS total score was found to have significant negative correlations with the 10-m sprint (r=-0.444, P=0.017), 30-m sprint (r=-0.425, P=0.016), and arrowhead agility tests (right, r=-0.389, P=0.023). These results suggest that higher FMS total scores could have a positive effect on the physical performance of the players.

#4 Comparison of three types of warm-up upon sprint ability in experienced soccer players
Reference: J Sport Health Sci. 2019 Nov;8(6):574-578. doi: 10.1016/j.jshs.2016.05.006. Epub 2016 May 24.
Authors: van den Tillaar R, Lerberg E, von Heimburg E
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Summary: The study aimed to compare the effects of a long general warm-up, a long specific warm-up, and a short specific warm-up upon sprint ability in soccer players. Twelve male soccer players (age: 18.3 ± 0.8 years, mean ± SD; body mass: 76.4 ± 7.2 kg; body height: 1.79 ± 0.05 m) conducted 3 types of warm-ups with 1 week in between: a long general warm-up, a long specific warm-up, and a short specific warm-up followed by 3 sprints of 40 m each. The best, average, and total sprinting times together with heart rate and ratings of perceived exertion were measured. The sprint times (best, average, and total time) were significantly better when performing a long specific or short specific warm-up compared with the long general warm-up (all p < 0.05). The received perception exertion was significantly lower during the specific short warm-up (4.92 ± 0.90) compared with the longer ones (6.00 ± 0.74 and 6.25 ± 0.87, respectively). Specificity is more important in a warm-up routine before sprint performance than the duration of the warm-up.

#5 The effect of fatigue and duration knowledge of exercise on kicking performance in soccer players
Reference: J Sport Health Sci. 2019 Nov;8(6):567-573. doi: 10.1016/j.jshs.2016.02.001. Epub 2016 Feb 2.
Authors: Ferraz RMP, van den Tillaar R, Pereira A, Marques MC
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Summary: The purpose of this study was to investigate the influence of fatigue upon kicking maximal ball velocity and the target-hitting accuracy of soccer players; and also to examine the effect of the knowledge of the exercise duration upon these 2 parameters. Twenty-four semi-professional soccer players participated in this study and performed maximal instep kicks before and after the implementation of an exercise protocol, either with or without knowledge of the duration of this protocol. A mixed model of analysis of variance showed that kicking maximal ball velocity was significantly affected (F(5, 85) = 11.6, p < 0.001, η 2 = 0.39) but only after just 1 circuit of the fatigue protocol and then remained similar. Accuracy did not change during the protocol (F(5, 75) = 0.23, p = 0.76, η 2 = 0.03) and knowing the duration of exercitation did not affect accuracy and velocity development (F(1, 23) ≤ 1.04, p ≥ 0.32, η 2 ≤ 0.06). These findings demonstrated the potential negative effects of fatigue on kicking ball velocity in soccer but not in the kicking accuracy and that the effect of fatigue may not be progressive over time. Knowing or not knowing the duration of exercitation did not affect the results.

#6 Effect of contextual factors in body composition of professional soccer players. A retrospective study
Reference: Nutr Hosp. 2019 Nov 13. doi: 10.20960/nh.02783. [Epub ahead of print] [Article in Spanish]
Authors: López Cáceres PA, Chena M, Asín Izquierdo I, Moreno-Ortega A, Moreno Rojas R
Summary: The requirements of physical demands in soccer have evolved in recent years, determining the need to investigate those aspects that condition athletic performance. The objective of this study was to describe the incidence of individualized training, company at meals, race, and demarcation on the anthropometric variables of professional soccer players since these four factors affect body composition, which is considered a predictor of performance and an indicator of lifestyle in these individuals. For this purpose, a retrospective study was developed in 51 professional players of the Spanish Football League Second Division B during the 2015/2016, 2016/2017, and 2017/2018 seasons. The anthropometric assessment was carried out under the technical standards of measurement recommended by the International Working Group of Kinanthropometry, adopted by the International Society for the Advancement of Kinanthropometry (ISAK). The results revealed that individualized training and company during meals were the factors that most influence exerted on the anthropometric variables that were collected. The values of fat mass and muscle mass, and the sum of fold measurements are sensitive to the effect of the intervention with these factors. The highest levels of interaction occurred between company during the meals and individualized training, and between demarcation and company during the meals. Considering body composition as an aspect to be taken into account in the development of performance, it should be considered that the application of certain training contents according to the individual characteristics and lifestyle of players are factors that may have a significant influence on professional soccer players.

#7 A case study of the use of verbal reports for talent identification purposes in soccer: A Messi affair!
Reference: PLoS One. 2019 Nov 12;14(11):e0225033. doi: 10.1371/journal.pone.0225033. eCollection 2019.
Authors: Reeves MJ, McRobert AP, Lewis CJ, Roberts SJ
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Summary: Using a two-study approach, the main purpose of this case study was to explore the use of a verbal reporting methodology to better understand the thought processes of soccer talent scouts during an in-situ talent identification environment. Study 1 developed a standardized coding-scheme to examine verbal cognitions during a single soccer game. Study 2 then utilized this methodology to examine two full-time recruitment staff trained in the use of concurrent verbal reporting before undertaking a live, in-game task. Participants also participated in a debrief interview following the game. The findings of the two studies suggest that developing a verbal reporting protocol is viable, however when applied in a live-game environment it is problematic. Future research should therefore consider a modified version of this task to further explore the cognitions of scouts whilst observing and identifying potential talent.

#8 Late Activation of the Vastus Medialis in Determining the Risk of Anterior Cruciate Ligament Injury in Soccer Players
Reference: J Sport Rehabil. 2019 Nov 7:1-4. doi: 10.1123/jsr.2019-0026. [Epub ahead of print]
Authors: Marotta N, Demeco A, de Scorpio G, Indino A, Iona T, Ammendolia A.
Summary: Activation time of the quadriceps is important in determining injury risk in professional soccer players. The objective was to compare the activation time of the quadriceps and hamstrings muscles during a movement that puts stress on anterior cruciate ligament (ACL) to assess the risk of ACL injury. Twenty (10 males and 10 females) professional soccer players participated in this study. An inertial sensor and 4 electrodes positioned on the quadriceps and hamstrings muscles were used for the surface electromyography. The athlete resting on 1 leg dropped, from a 32-cm-high platform, on the suspended foot (testing leg), without jumping or lowering his center of gravity and maintaining single-leg landing for 5 seconds. Using a software, it is possible to calculate the activation time of the rectus femoris, vastus medialis (VM), biceps femoris, and semimembranosus muscles before ground contact. The main outcome was to evaluate the activation times of the rectus femoris, VM, biceps femoris, and semitendinosus muscles before ground contact in comparison with the range of normality calculated by the manufacturer. All male soccer players demonstrated a low risk related to the correct activation of all the examined muscles, while female soccer players demonstrated delayed activation of the VM. Delayed activation of the VM registered in females determines an increase in anterior shear force, which is an important risk factor for incurring an ACL injury. This testing protocol becomes adequate for the screening of high-risk athletes and for targeting interventions to specific imbalances that may increase injury risk.

#9 Poor Sleep Quality's Association With Soccer Injuries: Preliminary Data
Reference: Int J Sports Physiol Perform. 2019 Nov 10:1-6. doi: 10.1123/ijspp.2019-0185. [Epub ahead of print]
Authors: Silva A, Narciso FV, Soalheiro I, Viegas F, Freitas LSN, Lima A, Leite BA, Aleixo HC, Duffield R, de Mello MT.
Summary: The purpose was to investigate the relationship between sleep quality and quantity and injuries in elite soccer players and to compare sleep-wake variables and injury characteristics. The current investigation was a prospective cohort study of 23 elite male soccer players competing for 2 teams over 6 mo in the highest-level Brazilian competition. The players' sleep behavior was monitored for 10 d in the preseason using self-reporting sleep diaries and wrist activity monitors to determine sleep duration and quality. Furthermore, injuries were recorded by the respective club's medical teams into a specific database. Details of injuries recorded included the type, location, and severity of each injury. The results were expressed as descriptive statistics, and the significance level was set at 5%. The Mann-Whitney U test was performed to compare the sleep variables between groups. Spearman correlation coefficient and linear-regression analysis were used. The results indicated a moderate negative correlation between sleep efficiency and particular injury characteristics, including absence time, injury severity, and amount of injuries. The linear-regression analysis indicated that 44% of the total variance in the number of injuries can be explained by sleep efficiency, 24% of the total variance in the absence time after injury (days) can be explained by sleep efficiency, and 47% of the total variance in the injury severity can be explained by sleep efficiency. Soccer players who exhibit lower sleep quality or nonrestorative sleep show associations with increased number and severity of musculoskeletal injuries.

#10 Was Zika introduced to Brazil by participants at the 2013 Beach Soccer World Cup held in Tahiti: A phylogeographical analysis
Reference: Travel Med Infect Dis. 2019 Nov 5:101512. doi: 10.1016/j.tmaid.2019.101512. [Epub ahead of print]
Authors: Le Hingrat Q, Perrier M, Charpentier C, Jacquot A, Houhou-Fidouh N, Descamps D, Visseaux B
Summary: Zika virus (ZIKV) was initially responsible for a limited number of punctual epidemics throughout Africa and Asia. Recently, large epidemics occurred in French Polynesia, Brazil and Pan-America. These outbreaks were associated with severe outcomes such as Guillain-Barré Syndrome and microcephaly of in-utero infected newborns. Previous studies demonstrated that ZIKV was introduced in Brazil from French Polynesia but failed to identify a founding event. All publicly available ZIKV full-genome sequences (n = 182) were phylogenetically analyzed, using Bayesian method, to estimate the introduction date of ZIKV into Brazil. Introduction date into Brazil was estimated between 8th of July 2013 and 4th of November 2013, encompassing the Beach Soccer World Cup held in French Polynesia, in September 2013, which gathered Brazilian athletes and supporters. We also observed that ZIKV sequences from travelers infected in South-East Asia or in Pacific islands were closely related to viruses identified prior to the French Polynesian epidemic, underlining an endemic circulation of ZIKV in those countries since 2007, at least. This work provides a narrower estimation of ZIKV introduction into Brazil and illustrates the need for a better exploration of ZIKV circulation and endemicity in South-East Asia, while epidemiological and prevention efforts have been mainly focused on the Pan-American epidemic.

#11 Constructing Spaces and Times for Tactical Analysis in Football
Reference: IEEE Trans Vis Comput Graph. 2019 Nov 8. doi: 10.1109/TVCG.2019.2952129. [Epub ahead of print]
Authors: Andrienko G, Andrienko N, Anzer G, Bauer P, Budziak G, Fuchs G, Hecker D, Weber H, Wrobel S.
Summary: A possible objective in analyzing trajectories of multiple simultaneously moving objects, such as football players during a game, is to extract and understand the general patterns of coordinated movement in different classes of situations as they develop. For achieving this objective, we propose an approach that includes a combination of query techniques for flexible selection of episodes of situation development, a method for dynamic aggregation of data from selected groups of episodes, and a data structure for representing the aggregates that enables their exploration and use in further analysis. The aggregation, which is meant to abstract general movement patterns, involves construction of new time-homomorphic reference systems owing to iterative application of aggregation operators to a sequence of data selections. As similar patterns may occur at different spatial locations, we also propose constructing new spatial reference systems for aligning and matching movements irrespective of their absolute locations. The approach was tested in application to tracking data from two Bundesliga games of the 2018/2019 season. It enabled detection of interesting and meaningful general patterns of team behaviors in three classes of situations defined by football experts. The experts found the approach and the underlying concepts worth implementing in tools for football analysts.

#12 The real penalty: number of OMFS patients presenting to the emergency department at Sunderland Royal Hospital after England fixtures before and during the 2018 FIFA Football World Cup
Reference: Br J Oral Maxillofac Surg. 2019 Nov 9. pii: S0266-4356(19)30709-0. doi: 10.1016/j.bjoms.2019.10.313. [Epub ahead of print]
Authors: Miller N, Kearns A, Bartram A, Banks R
Summary: The aim of this study was to establish a link between a large televised sporting event and the incidence of patients presenting to the emergency department with oral and maxillofacial injuries. When compared with daily attendances throughout the year, the mean (SD) number rose from 2.53 (1.69) to 4.00 (1.53) (p=0.005) between 1 November 2017 and 31 July 2018 on the day after an England fixture, an increase of 58%. These data show the need for workforce planning during large-scale national sporting events because of the rise in the number of patients presenting. They show that the increase in workload is caused by a higher number of both traumatic and non-traumatic injuries.

#13 Yo-Yo intermittent tests are a valid tool for aerobic fitness assessment in recreational football
Reference: Eur J Appl Physiol. 2019 Nov 9. doi: 10.1007/s00421-019-04258-8. [Epub ahead of print]
Authors: Castagna C, Krustrup P, Póvoas S
Summary: The purpose was to examine the suitability of three versions and two levels of the Yo-Yo intermittent tests for assessing and tracking aerobic fitness status development in male recreational football players. Sixty-six untrained participants (age 39 ± 6 years, VO2max 41.2 ± 6.2 ml kg-1 min-1, body mass 81.9 ± 10.8 kg, height 173.2 ± 6.4 cm) partook in a 12-week recreational football training program. They were evaluated during the Yo-Yo intermittent endurance level 1 (YYIE1) and 2 (YYIE2) tests and the Yo-Yo intermittent recovery level 1 test (YYIR1), and during a treadmill test for VO2max assessment, at baseline. Thirty-two out of these 66 participants replicated all these tests at post-intervention. An additional group of 30 male age-matched recreational football players that afterwards started the 12-week recreational football program (age 39 ± 6 years, VO2max 45.3 ± 5.8 ml kg-1 min-1, body mass 82.5 ± 7.8 kg, height 172.8 ± 5.4 cm) was evaluated at baseline to test cross-validation. The Yo-Yo tests showed very large associations with VO2max at baseline (r = 0.75-0.77; P < 0.0001) and at post-intervention (r = 0.76-0.82; P < 0.0005). Post-training, very large associations were found between YYIE2 performance and VO2max (r = 0.65, P < 0.0001). Cross-validation revealed small to large differences between the observed and estimated VO2max values (1.5-2.96 ml kg-1 min-1) with moderate typical error of estimation (7.9-8.7%) across the tests. Performance in the YYIE1, YYIE2 and YYIR1 tests of ≥ 1760, 480 and 600 m, respectively, indicated good to excellent VO2max values. The Yo-Yo tests considered here showed robust and consistent criterion validity. The YYIE2 could be a more accurate option to track aerobic fitness development in recreational football players.





Latest research in football - week 47 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 An Evaluation of Heart Rate Variability in Female Youth Soccer Players Following Soccer Heading: A Pilot Study
Reference: Sports (Basel). 2019 Nov 4;7(11). pii: E229. doi: 10.3390/sports7110229.
Authors: Harriss AB, Abbott K, Kimpinski K, Holmes JD, Johnson AM, Walton DM, Dickey JP
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Summary: Most head impacts in soccer occur from purposeful heading; however, the link between heading and neurological impairment is unknown. Previous work suggests concussion may result in an uncoupling between the autonomic nervous system and cardiovascular system. Accordingly, heart rate variability (HRV) may be a sensitive measure to provide meaningful information regarding repetitive heading in soccer. The purpose of this pilot study assesses the feasibility of measuring HRV to evaluate autonomic function following soccer heading. Sixteen youth female participants underwent heart rate monitoring during a heading and footing condition. Participants completed a five minute resting supine trial at the start and end of each testing session. Standard 450 g soccer balls were projected at 6 m/s towards participants. Participants performed five headers, for the header condition, and five footers for the footer condition. The HRV for resting supine trials, pre- and post-header and footer conditions were assessed for both time and frequency domains. HRV effect sizes were small when comparing conditions, except absolute low frequency (d = 0.61) and standard deviation of the normal-normal (NN) intervals (d = 0.63). Participant retention and adherence were high, without adverse events. Findings suggest HRV is a feasible measure for evaluating the effects of heading on autonomic function.

#2 Combined Anterolateral, Anterior, and Anteromedial Ankle Impingement in an Adolescent Soccer Player: A Case Report and Review of the Literature
Authors: Cosma DI, Vasilescu DE, Corbu A, Todor A, Valeanu M, Ulici A
Summary: A unique case of combined anterolateral, anterior, and anteromedial ankle impingement in an adolescent soccer player is presented in this article. To the best of our knowledge, this is the only report of circumferential, massive, anterior ankle impingement in children described in the literature. The importance of proper diagnosis and treatment of such a lesion is illustrated in this case report. We also emphasize that clinical examination combined with 3D computed tomography scan reconstruction is an excellent and cost-effective imaging modality that can help with the diagnosis of anterior ankle impingement. Finally, open surgical treatment showed excellent results in an elite athlete.

#3 Defining the Process of a Cardiovascular Risk Assessment Program: Lessons Learned From Cardiac Assessment of Elite Soccer Players in the United Kingdom
Reference: Clin J Sport Med. 2019 Nov;29(6):500-505. doi: 10.1097/JSM.0000000000000534.
Authors: Speers C, Seth AN, Patel KC, Rakhit DJ, Gillett MJ
Summary: Retrospectively analyze the cardiac assessment process for elite soccer players, and provide team physicians with a systematic guide to managing longitudinal cardiac risk. Cardiac assessments incorporating clinical examination, 12-lead ECG, echocardiography, and health questionnaire were utilized in this study.  Soccer players at 5 professional clubs in England, the United Kingdom participated. Data was retrospectively collected, inspected, and analyzed to determine their clinical management and subsequent follow-up. Over 2 years, 265 soccer players, aged 13 to 37 years with 66% of white European ethnicity, were included in the cohort. Eleven percent had "not-normal" assessments, of these assessments, 83% were considered gray screens, falling into three broad categories: structural cardiac features (including valvular abnormalities), functional cardiac features, and electrocardiogram changes. After cardiology consultation, all assessments were grouped into low, enhanced and high-risk categories for ongoing longitudinal risk management. Overall clear-cut pathology was identified in 2%. Cardiovascular assessment is a vital tool in identifying athletes at risk of sudden cardiac death to mitigate their risk through surveillance, intervention, or participation restriction. The decision whether a player is fit to play or not requires a robust risk assessment followed by input from a multidisciplinary team that includes both the team physician and cardiologist. This educational article proposes a clinical management pathway to aid clinicians with this process. Sudden cardiac death is the important medical cause of death during exercise. The team physician should assume responsibility for the management of the longitudinal risk of their players' cardiac assessments in conjunction with sports cardiologist.

#4 Effects of a Computerized Training on Attentional Capacity of Young Soccer Players
Reference: Front Psychol. 2019 Oct 21;10:2279. doi: 10.3389/fpsyg.2019.02279. eCollection 2019.
Authors: Reigal RE, González-Guirval F, Morillo-Baro JP, Morales-Sánchez V, Juárez-Ruiz de Mier R, Hernández-Mendo A
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Summary: The purpose of this work was to analyze the effects of a computerized training on attentional capacity in a group of young soccer players. Seventy-five male adolescents from two soccer clubs in the city of Malaga (Spain) and aged between 14 and 18 (15.45 ± 1.43 years) participated in the investigation. A quasi-experimental design was used, and the adolescents were divided into control (n = 38) and experimental (n = 37) groups. The experimental group underwent a computerized training (Rejilla 1.0) of their attention during 9 weeks and 27 sessions. In addition, the D2 attention test was used to analyze the evolution of participants after the intervention program. The results showed positive effects of the computerized intervention program on selective attention, observing changes both in the executions of the software used (p < 0.001, Cohen's d = 1.58, 95% CI [1.06, 2.11]) and in the main measures of the D2 test, total effectiveness (p < 0.001, Cohen's d = 0.62, 95% CI [0.15, 1.08]) and concentration (p < 0.01, Cohen's d = 0.48, 95% CI [0.02, 0.94]).

#5 Growth pattern of lumbar bone mineral content and trunk muscles in adolescent male soccer players
Reference: J Bone Miner Metab. 2019 Nov 7. doi: 10.1007/s00774-019-01060-6. [Epub ahead of print]
Authors: Takei S, Taketomi S, Tanaka S, Torii S
Summary: Previous studies have reported that the peak in lean body mass (LBM) precedes the peak in bone mineral content (BMC). However, it is unknown whether the trunk region growth is similar. We investigated the difference between pubertal peak age in the increase of LBM in the trunk (trunk LBM) and pubertal peak age in the increase of BMC in the lumbar spine (lumbar BMC) in a longitudinal study of 201 Japanese male adolescent soccer players. The age of peak height velocity (PHV) and the developmental age were calculated. The participants were followed over a 2-year period, with height and dual-energy X-ray absorptiometry scans taken every 6 months. The trunk LBM (ρ = 0.732, p < 0.0001) and the lumbar BMC (ρ = 0.621, p < 0.0001) significantly correlated with the developmental age. The increase of trunk LBM and lumbar BMC was significantly different according to the developmental stages (Kruskal-Wallis test; p < 0.0001 and p < 0.001, respectively). We used a cubic spline to estimate the developmental age, when the increase reached its peak: the peak age of the increase in trunk LBM was estimated to be - 0.08 years (approximately - 1 month) prior to PHV age, whereas the peak age of the increase in lumbar BMC was estimated to be 0.42 years (approximately 5 months) after the PHV age. The maximal increase in trunk LBM occurs just before PHV age and approximately 6 months before the maximal increase in lumbar BMC during the pubertal growth spurt in the Japanese adolescent male soccer players.

#6 The impact of endurance training and table soccer on brain metabolites in schizophrenia
Reference: Brain Imaging Behav. 2019 Nov 5. doi: 10.1007/s11682-019-00198-1. [Epub ahead of print]
Authors: Rauchmann BS, Ghaseminejad F, Keeser D, Keller-Varady K, Schneider-Axmann T, Takahashi S, Karali T, Helms G, Dechent P, Maurus I, Hasan A, Wobrock T, Ertl-Wagner B, Schmitt A, Malchow B, Falkai P
Summary: Higher glutamate and glutamine (together: Glx) and lower N-acetyl-aspartate (NAA) levels were reported in schizophrenia. Endurance training normalizes NAA in the hippocampus, but its effects on other metabolites in the brain and the relationship of metabolites to clinical symptoms remain unknown. For 12 weeks, 20 schizophrenia inpatients (14 men, 6 women) and 23 healthy controls (16 men, 7 women) performed endurance training and a control group of 21 schizophrenia inpatients (15 men, 6 women) played table soccer. A computer-assisted cognitive performance training program was introduced after 6 weeks. We assessed cognitive performance, psychopathological symptoms, and everyday functioning at baseline and after 6 and 12 weeks and performed single voxel magnetic resonance spectroscopy of the hippocampus, left dorsolateral prefrontal cortex (DLPFC), and thalamus. We quantified NAA, Glx, total creatine (tCr), calculated NAA/tCr and Glx/tCr and correlated these ratios with physical fitness, clinical and neurocognitive scores, and everyday functioning. At baseline, in both schizophrenia groups NAA/tCr was lower in the left DLPFC and left hippocampus and Glx/tCr was lower in the hippocampus than in the healthy controls. After 6 weeks, NAA/tCr increased in the left DLPFC in both schizophrenia groups. Brain metabolites did not change significantly in the hippocampus or thalamus, but the correlation between NAA/tCr and Glx/tCr normalized in the left DLPFC. Global Assessment of Functioning improvements correlated with NAA/tCr changes in the left DLPFC. In our study, endurance training and table soccer induced normalization of brain metabolite ratios in the brain circuitry associated with neuronal and synaptic elements, including metabolites of the glutamatergic system.

#7 Maximal oxygen consumption and oxygen muscle saturation recovery following repeated anaerobic sprint test in youth soccer players
Reference: J Sports Med Phys Fitness. 2019 Oct 28. doi: 10.23736/S0022-4707.19.10162-4. [Epub ahead of print]
Authors: Michailidis Y, Chatzimagioglou A, Mikikis D, Ispirlidis I, Metaxas T
Summary: The purpose of the study was to examine whether differences in aerobic capacity (VO2max) influence muscle reoxygenation following repeated anaerobic sprint test (RAST) in soccer players. We hypothesized that muscle reoxygenation is faster in players with higher aerobic capacity. Ten male, youth soccer players participated in the study and performed RAST on a synthetic grass field. Oxygen saturation in muscle (StO2) of the right vastus lateralis muscle was measured by near-infrared spectroscopy. Half the time that was required for StO2 recovery (T1/2 StO2) after RAST was used to evaluate the reoxygenation in the recovery period after testing. The T1/2 StO2 was defined as the time from the end of RAST testing to the time of reaching 50% of StO2. Aerobic capacity (VO2max) was estimated by the Yo-Yo intermittent recovery test level 1 (YYIR1). The T1/2 StO2 had a significant inverse correlation with VO2max (r=-0.71; P=0.021) and with the distance which was covered by players on YYIR1 test (r=-0.71; P=0.021). In contrast, StO2 recovery rate showed no significant correlations with the VO2max in subjects. These results indicate that aerobic capacity can influence vastus lateralis reoxygenation following RAST in youth soccer players.

#8 Match Performance of Soccer Teams in the Chinese Super League-Effects of Situational and Environmental Factors
Reference: Int J Environ Res Public Health. 2019 Nov 1;16(21). pii: E4238. doi: 10.3390/ijerph16214238.
Authors: Zhou C, Hopkins WG, Mao W, Calvo AL, Liu H
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Summary: The purpose of the study was to investigate the effects of situational factors (match location, strength of team and opponent) and environmental factors (relative air humidity, temperature and air quality index) on the technical and physical match performance of Chinese Soccer Super League teams (CSL). The generalized mixed modelling was employed to determine the effects by using the data of all 240 matches in the season 2015 collected by Amisco Pro®. Increase in the rank difference would increase the number of goal-scoring related, passing and organizing related actions to a small-to-moderate extent (Effect size [ES]: 0.37-0.99). Match location had small positive effects on goal-scoring related, passing and organizing related variables (ES: 0.27-0.51), while a small negative effect on yellow card (ES = -0.35). Increment in relative air humidity and air quality index would only bring trivial or small effects on all the technical performance (ES: -0.06-0.23). Increase in humidity would decrease the physical performance at a small magnitude (ES: -0.55--0.38). Teams achieved the highest number in the physical performance-related parameters at the temperature between 11.6 and 15.1 °C. In the CSL, situational variables had major effects on the technical performance but trivial effects on the physical performance, on the contrary, environmental factors affected mainly the physical performance but had only trivial or small impact on the technical performance.

#9 Psychological Intervention Program to Control Stress in Youth Soccer Players
Reference: Front Psychol. 2019 Oct 16;10:2260. doi: 10.3389/fpsyg.2019.02260. eCollection 2019.
Authors: Olmedilla A, Moreno-Fernández IM, Gómez-Espejo V, Robles-Palazón FJ, Verdú I, Ortega E
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Summary: The influence on the psychological well-being of the players and their sports performance seems to be one of the keys to the current sports practice. The purpose of this study was to determine the effectiveness of a psychological intervention program for stress control in youth soccer players. A total sample of 19 male youth soccer players (age: 16.3 ± 0.99 years; years playing soccer: 10.89 ± 1.56 years) completed the current research. The Psychological Characteristics Questionnaire related to Sports Performance (CPRD) was used to assess stress factors related to sports competition. A program based on Cognitive-Behavioral Therapy was implemented during eight sessions of approximately 50 min each. A pre-post design was used and statistical differences between pre- and post-measures were checked through dependent sample t-tests. The results indicated that the post-test scores were higher than the pre-tests in "Influence of the Evaluation of Performance" and "Mental Skills" factors, which supposes a significant improvement of the stress management related to performance evaluation, as well as the use of psychological resources and techniques. In addition, the post-test scores were also higher in the "Stress Control" factor, although in this case the differences were not statistically significant. Practical indications deriving from the findings of this study can help youth soccer players to manage the stress of competition using a psychological training program.

#10 The effectiveness of a practical half-time re-warm-up strategy on performance and the physical response to soccer-specific activity
Reference: J Sports Sci. 2019 Nov 2:1-10. doi: 10.1080/02640414.2019.1686941. [Epub ahead of print]
Authors: Fashioni E, Langley B, Page RM
Summary: The aim of this study was to assess the influence of a half-time (HT) re-warm up (RWU) strategy on measures of performance and the physical and perceptual response to soccer-specific activity. Ten male soccer players completed a control (CON) and RWU trial, in which participants completed 60 min (4 x 15-min periods with a 15-min HT interspersing the third and fourth periods) of a soccer-specific exercise protocol. The CON trial comprised a passive 15-min HT, whilst the RWU trial comprised a passive 12-min period, followed by a 3-min RWU. The RWU elicited an improvement in 20 m sprint times (d= 0.6; CON: 3.42 ± 0.20 s; RWU: 3.32 ± 0.12 s), and both squat (d= 0.6; CON: 26.96 ± 5.00 cm; RWU: 30.17 ± 5.13 cm) and countermovement jump height (d= 0.7; CON: 28.15 ± 4.72 cm; RWU: 31.53 ± 5.43 cm) following the RWU and during the initial stages of the second half. No significant changes were identified for 5 m or 10 m sprint performance, perceived muscle soreness, or PlayerLoadTM. Ratings of perceived exertion were however higher (~2 a.u) following the RWU. These data support the use of a HT RWU intervention to elicit acute changes in performance.

#11 The adolescent motor performance development of elite female soccer players: A study of prognostic relevance for future success in adulthood using multilevel modelling
Reference: J Sports Sci. 2019 Nov 2:1-10. doi: 10.1080/02640414.2019.1686940. [Epub ahead of print]
Authors: Leyhr D, Raabe J, Schultz F, Kelava A, Höner O
Summary: Considering the scarce empirical evidence regarding talent predictors in female youth soccer, the present study aimed to investigate the long-term prognostic validity of elite female soccer players' adolescent motor performance for future success in adulthood. Additionally, the three-year development of highly talented girls' motor performance and the predictive value of this motor development for reaching a professional adult performance level (APL) was analysed.Overall, N = 737 female players participated in nationwide motor diagnostics (sprinting, agility, dribbling, ball control, shooting) within the German Soccer Association's talent identification and development programme at least twice between the age groups Under-12 (U12) and U15. Based on their APL at least four years later, participants were assigned to a professional (first German division, 6.2%) or non-professional group (lower divisions, 93.8%).Multilevel regression analyses revealed a general prognostic relevance for the investigated parameters with respect to players' APL. In addition, there was a non-linear improvement in participants' motor performance across all variables from U12 to U15. However, non-significant interactions between APL and these improvements indicate motor performance development itself cannot adequately predict players' future success in adulthood. Findings provide insightful information that can help coaches foster optimal support for young female soccer players' development.





Latest research in football - week 46 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 A public data set of spatio-temporal match events in soccer competitions
Reference: Sci Data. 2019 Oct 28;6(1):236. doi: 10.1038/s41597-019-0247-7.
Authors: Pappalardo L, Cintia P, Rossi A, Massucco E, Ferragina P, Pedreschi D, Giannotti F
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Summary: Soccer analytics is attracting increasing interest in academia and industry, thanks to the availability of sensing technologies that provide high-fidelity data streams for every match. Unfortunately, these detailed data are owned by specialized companies and hence are rarely publicly available for scientific research. To fill this gap, this paper describes the largest open collection of soccer-logs ever released, containing all the spatio-temporal events (passes, shots, fouls, etc.) that occured during each match for an entire season of seven prominent soccer competitions. Each match event contains information about its position, time, outcome, player and characteristics. The nature of team sports like soccer, halfway between the abstraction of a game and the reality of complex social systems, combined with the unique size and composition of this dataset, provide an ideal ground for tackling a wide range of data science problems, including the measurement and evaluation of performance, both at individual and at collective level, and the determinants of success and failure.

#2 Soccer Injuries in Children and Adolescents
Reference: Pediatrics. 2019 Nov;144(5). pii: e20192759. doi: 10.1542/peds.2019-2759.
Authors: Watson A, Mjaanes JM
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Summary: Participation in youth soccer in the United States continues to increase steadily, with a greater percentage of preadolescent participants than perhaps any other youth sport. Despite the wide-ranging health benefits of participation in organized sports, injuries occur and represent a threat to the health and performance of young athletes. Youth soccer has a greater reported injury rate than many other contact sports, and recent studies suggest that injury rates are increasing. Large increases in the incidence of concussions in youth soccer have been reported, and anterior cruciate ligament injuries remain a significant problem in this sport, particularly among female athletes. Considerable new research has identified a number of modifiable risk factors for lower-extremity injuries and concussion, and several prevention programs have been identified to reduce the risk of injury. Rule enforcement and fair play also serve an important role in reducing the risk of injury among youth soccer participants. This report provides an updated review of the relevant literature as well as recommendations to promote the safe participation of children and adolescents in soccer.

#3 Arachnoid cyst in young soccer players complicated by chronic subdural hematoma: personal experience and review of the literature
Reference: Acta Neurol Belg. 2019 Oct 25. doi: 10.1007/s13760-019-01224-1. [Epub ahead of print]
Authors: Gregori F, Colistra D, Mancarella C, Chiarella V, Marotta N, Domenicucci M
Summary: Arachnoid cysts (ACs) are congenital intracranial benign cavities originating from the meninges during embryological development. Several studies have shown the existence of a relationship between AC and a higher risk to develop ipsilateral chronic subdural hematoma (CSH) especially in a young population. In the presence of an AC, the practice of sport activities may expose young patients to minor head trauma and to an increased risk of developing CSH. We describe three cases of young soccer players with AC associated with CSH. Then, we performed a literature review of all the reported cases in the literature of patients younger than 18 years with AC-associated CSH related to sport practice. A total of 33 cases, including the three cases reported by us, are analyzed. Soccer is the most represented sport activity in this association (39% of cases). The treatment of choice is surgical in all patients, with burr hole or craniotomy in similar proportions. In one-third of patients, the AC has been fenestrated. Outcome is good in all the reported cases. We reviewed the main pathogenic theories, the main surgical strategies described in literature, as well as recurrence rate of CSH, the association of AC and cranial deformities, and the clinical outcome. AC might be associated with skull deformities, but their real incidence remains unclear. The clinical detection of such anomalies should suggest performing further radiological investigations. If the presence of AC is confirmed, the practice of sport activities should not be avoided, as the real incidence of AC-associated CSH is not clear yet and the reported outcomes in literature are good. Surgical treatment of AC-associated CSH should be hematoma removal through burr hole, reserving AC fenestration only for cases with intracystic bleeding or recurrences. The surgeon should adequately advise and inform the young patients and their families that they could have an increased risk of developing CSH given by the presence of the AC, and that they should be referred to a neurosurgical center if they become symptomatic.

#4 Prevalence of Relative Age Effect in Russian Soccer: The Role of Chronological Age and Performance
Reference: Int J Environ Res Public Health. 2019 Oct 23;16(21). pii: E4055. doi: 10.3390/ijerph16214055.
Authors: Bezuglov EN, Nikolaidis PT, Khaitin V, Usmanova E, Luibushkina A, Repetiuk A, Waśkiewicz Z, Gerasimuk D, Rosemann T, Knechtle B
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Summary: The relative age effect (RAE) has been well studied in adolescent and adult soccer players; however, less information has been available about children engaged in regular soccer training and the role of performance. Thus, the aim of the present study was to examine the prevalence of RAE in children and adolescent soccer players, as well as the role of age and performance. Russian soccer players (n = 10,446) of various ages, playing positions and performance levels were examined for their date of birth. It was observed that RAE was widespread in Russian soccer teams of all age groups. RAE was most pronounced in children teams of the top tier Russian soccer academies and junior Russia national teams, where the proportions of soccer players born in the first quarter were 43.9% and 39.8%, respectively, whereas those born in the fourth quarter of the year were 7.7% and 6.3%, respectively. In top tier soccer academies, RAE did not vary by age group. In the middle tier soccer academies, RAE was less pronounced. It was still prevalent in the junior teams of the top tier clubs of the Russian Premier League, where 14.3% of the soccer players were born in the fourth quarter of the year compared to 42.9% born in the first quarter of the year. RAE can be observed in the top tier Russian adult teams as well, although it is less pronounced there. In summary, RAE is highly prevalent in Russian children and junior soccer and is associated with the level of competitiveness. At the same time, the proportion of players born in the fourth quarter of the year is higher in adult teams than in junior and youth teams, which is most likely due to the wider selection of players, not limited by their age and place of residence. In junior teams, RAE results in a bias towards selection of players who are more physically mature, whereas children who may be more talented but are less developed due to their younger chronological age tend to be overlooked.

#5 Women Are at Higher Risk for Concussions Due to Ball or Equipment Contact in Soccer and Lacrosse
Reference: Clin Orthop Relat Res. 2019 Oct 17. doi: 10.1097/CORR.0000000000000995. [Epub ahead of print]
Authors: Ling DI, Cheng J, Santiago K, Ammerman B, Jivanelli B, Hannafin J, Casey E
Summary: There is ample evidence to suggest sex- and gender-based differences in the incidence of sports-related concussions. The mechanisms of concussion may vary between male and female athletes and contribute to this observed difference. Understanding the underlying etiology by pooling data from primary studies across different settings and sport types will inform interventions that can reduce concussion rates. Specifically, we asked: (1) In which sports are female athletes less likely to experience concussions from player contact? (2) In which sports are female athletes more likely to experience concussions because of ball or equipment contact? PubMed, EMBASE, and Cochrane Library databases were searched to identify articles published from January 2000 to December 2018. Ten studies met the inclusion criteria, which were studies that reported concussion incidence by mechanism for both male and female athletes. Exclusion criteria included non-English studies, conference abstracts, and studies on non-sports related concussions. The sports represented by the 10 studies included ice hockey (n = 4), soccer (n = 5), basketball (n = 4), baseball/softball (n = 4), and lacrosse (n = 5). The rate ratio was calculated as the incidence rate in female athletes/male athletes for each concussion mechanism or activity. Data were pooled using the DerSimonian-Laird random-effects model. Study quality was assessed with the Newcastle-Ottawa Scale. Female athletes were at lower risk of player-contact-induced concussions in lacrosse (pooled rate ratio 0.33 [95% CI 0.25 to 0.43]; p < 0.001), basketball (pooled rate ratio 0.86 [95% CI 0.76 to 0.97]; p = 0.01), ice hockey (pooled rate ratio 0.64 [95% CI 0.56 to 0.73]; p < 0.001), soccer (pooled rate ratio 0.70 [95% CI 0.66 to 0.75]; p < 0.001), and soccer heading (pooled rate ratio 0.80 [95% CI 0.72 to 0.90]; p < 0.001); in these sports, men were at higher risk of concussions from player contact. Female athletes were more likely to experience concussions because of ball or equipment contact in lacrosse (pooled rate ratio 3.24 [95% CI 2.10 to 4.99]; p < 0.001), soccer (pooled rate ratio 2.04 [95% CI 1.67 to 2.49]; p < 0.001), and soccer heading (pooled rate ratio 2.63 [95% CI 1.84 to 3.77]; p < 0.001). The mechanism or activity underlying concussions differs between male and female athletes across different sports. This finding remains the same regardless of whether there are rule differences between the men's and women's games. The implementation of other interventions are required to further ensure player safety, including protective head equipment, concussion prevention training, or rules limiting player contact in the men's game.

#6 Jump performance in male and female football players
Reference: Knee Surg Sports Traumatol Arthrosc. 2019 Oct 30. doi: 10.1007/s00167-019-05747-1. [Epub ahead of print]
Authors: Arundale AJH, Kvist J, Hägglund M, Fältström A
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Summary: The purpose was to examine differences between men and women football players in clinically feasible jumping measures. Female football players (N = 46, ages 16-25) were matched based on age, training frequency, and playing position with 46 male players. All players performed the tuck jump and drop vertical jump (DVJ). DVJ was assessed quantitatively for valgus knee motion and probability of a high peak knee abduction moment (pKAM), as well as sagittal plane hip, knee, and ankle angles, and qualitatively with visual assessment of the player's knees upon landing; graded as good, reduced, or poor control. Women had higher total tuck jump scores (5 ± 2) (more technique flaws), than men (3 ± 2, P < 0.01). The quantitative analysis of the DVJ found that men had greater asymmetries between limbs, but women landed bilaterally in more knee valgus (interaction P = 0.04, main effect of sex P = 0.02). There was no difference in pKAM (interaction n.s.). Women also landed in less hip flexion (P = 0.01) and ankle dorsiflexion (P = 0.01) than men. The qualitative DVJ analysis found that more women (48%) had poor knee control compared to men (11%, P < 0.01). The results indicate that women perform worse on the tuck jump assessment than men. The results support previous findings that women land in more knee valgus than men, but also found that men may have larger asymmetries in knee valgus. These results from clinically feasible measures provide some suggestions for clinicians to consider during ACL reconstruction rehabilitation to enhance performance.

#7 Game-specific abilities in elite youth football players: validity and sensitivity to change in subjective coach ratings compared to objectively assessed data
Reference: J Sports Med Phys Fitness. 2019 Oct 25. doi: 10.23736/S0022-4707.19.10084-9. [Epub ahead of print]
Authors: Niederer D, Damm M, Grigereit A, Banzer W, Vogt L
Summary: Little is known on the accuracy of coaches' ratings of game-specific physical abilities in elite youth football players. The present study on elite youth football players aims to assess whether 1) the coaches' subjective assessment of the level of performance of each athlete within the team is in accordance with objectively collected data and 2) the coaches rate changes in the athletes'' performance level accurately or not. Data on jumping ability, sprinting speed, change of direction and strength were collected in seven age groups at a football youth academy (n = 150). The diagnostic battery was repeated after seven months (n = 138). Before the second session, the head coaches completed Likert-scaled closed questions on 1) the importance of running speed and reactive strength components and their relevance to the individual game performance of each of their athletes, 2) level of performance of their athletes, and 3) the change between the first and second performance testing results. Validity and sensitivity of change of their ratings in comparison to the performance data were calculated using analyses of interrelationship. The data of the head coaches showed a low to medium effect size in the agreement with the performance data (Cohen's W = .33 - .71). The evaluation of the change in level of performance was poorer (Cohen's W =.04 - .2; n.s.). Our results underline that functional/physical testing twice during a season may be crucial for displaying performance levels of elite youth football players. Simple self-reported ratings by the coach may be valid in recent performance level assessment but not for performance changes.

#8 Internal training load monitoring in professional football: a systematic review of methods using rating of perceived exertion
Reference: J Sports Med Phys Fitness. 2019 Oct 24. doi: 10.23736/S0022-4707.19.10000-X. [Epub ahead of print]
Authors: Rago V, Brito J, Figueiredo P, Costa J, Krustrup P, Rebelo A
Summary: The rate of perceived exertion (RPE) is widely adopted to quantify internal training load (ITL) in professional football. The aim of this study was to systematically review the use RPE-based methods in professional football. Observational studies conducted during training routines of professional football players over a minimum of one- week were selected based on the preferred reporting items for systematic reviews and meta-analyses statement. Thirty-eight articles met the inclusion criteria (average qualitative score was 6.3 out of 10 [3 to 9]). The main deficiencies identified concerned the poor description of study design (~52% of the studies), and the non-quantification of match load (~44%). Ten studies complemented RPE-based ITL information with time-motion analysis (~26%) and seven studies added HR recordings (~18%). Nine studies collected RPE data after complementary training, separately to field sessions (~3%). Operational questions (e.g. How was your workout? ~71%) were preferred to instructions (e.g. Please rate the intensity of today's session; ~8%). Session-RPE (s-RPE; RPE multiplied by training duration) was more commonly adopted as measure of exercise intensity than isolated RPE (~76 vs. ~8%). RPE-derived variables calculated on weekly values included absolute week-to-week change, acute: chronic workload ratio, monotony and strain and were not frequently used (7 to 15%). Four studies (~11%) divided RPE in two components: respiratory and muscular. There is a lack of consensus for the use of RPE in professional football and "good practices" are warranted. This review might help practitioners regarding procedures to adopt in RPE data collection and interpretation.

#9 No association between perceived exertion and session duration with hamstring injury occurrence in professional football
Reference: Scand J Med Sci Sports. 2019 Oct 30. doi: 10.1111/sms.13591. [Epub ahead of print]
Authors: Lolli L, Bahr R, Weston M, Whiteley R, Tabben M, Bonanno D, Gregson W, Chamari K, Di Salvo V, van Dyk N
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Summary: Training and competition loads have emerged as modifiable composite risk factors of non-contact injury. Hamstring strains are the most common injuries in football with substantial burden on the individual player and club. Nevertheless, robust evidence of a consistent load-hamstring injury relationship in professional football is lacking. Using available data from the Qatar Stars League over three competitive seasons, this study investigated the separate and combined effects of perceived exertion and session duration on hamstring injury occurrence in a sample of 30 outfield football players. Load variables were calculated into 7-day, 14-day, 21-day, 28-day periods of data, and week-to-week changes for average ratings of perceived exertion (RPE; au) score and session-RPE (s-RPE; session-duration X score), plus the cumulative training and match minutes and s-RPE, respectively. Conditional logistic regression models estimated load-injury relationships per 2-within-subject standard deviation increments in each candidate variable. Associations were declared practically important based on the location of the confidence interval in relation to thresholds of 0.90 and 1.11 defining small beneficial and harmful effects, respectively. The uncertainty for the corrected odds ratios show that typically high within-subject increments in each candidate variable were not practically important for training- and match-related hamstring injury (95% confidence intervals range: 0.85 to 1.16). We found limited exploratory evidence regarding the value of perceived exertion and session duration as aetiological factors of hamstring injury in Middle-East professional football. Monitoring remains valuable to inform player load management strategies, but our exploratory findings suggest its role for type-specific injury risk determination appears empirically unsupported.

#10 Risk of acute and overuse injuries in youth elite soccer players: Body size and growth matter
Reference: J Sci Med Sport. 2019 Oct 10. pii: S1440-2440(19)30355-X. doi: 10.1016/j.jsams.2019.10.001. [Epub ahead of print]
Authors: Rommers N, Rössler R, Goossens L, Vaeyens R, Lenoir M, Witvrouw E, D'Hondt E
Summary: This study investigated anthropometric measures and growth as risk factors for overuse and acute injuries in younger (U10-U12) and older (U13-U15) elite level soccer players. Height, weight, and sitting height were measured at the start and the end of the 2016-2017 competitive season and growth velocities were calculated. Throughout the season, injuries were registered continuously by the (para-)medical staff of the included clubs. We analyzed the injury risk using multilevel Poisson regression models, accounting for club and team clustering. Of the included 314 players (11.7±1.7 years of age), 160 players sustained 133 overuse and 163 acute injuries (i.e. 106 injuries in 69 players of the younger group, 190 in 91 players of the older group). In the younger group, risk of overuse injuries was associated with an increase in leg length over the season (incidence rate ratio (IRR) 1.620 [95% CI 1.230-2.117]) and risk of acute injuries with relatively younger age (IRR 1.003 [95% CI 1.000-1.006]). In the older group, a higher leg length was associated with an increased risk of overuse injuries (IRR 1.055 [95% CI 1.011-1.108]), and a higher weight and a lower growth rate with an increased risk of acute injuries (IRR 1.043 [95% CI 1.021-1.067] and 0.903 [95% CI 0.831-0.981], respectively). Injury risk factors differ by age group and type of injury. The age-specific anthropometric and growth-related risk factors should be monitored and these risk profiles should be considered to manage injury risk effectively.

#11 Effects of Ramadan fasting on physical performances in soccer players: a systematic review
Reference: Tunis Med. 2019 Oct;97(10):1114-1131.
Authors: Chtourou H, Trabelsi K, Boukhris O, Ammar A, Shephard RJ, Bragazzi NL.
Summary: The purpose was to evaluate the effects of Ramadan fasting on physical performance measures in soccer players through a systematic appraisal of the literature. Systematic review Data sources: The entire content of two databases, PubMed/MEDLINE and Web of Science. Eligibility criteria for selecting studies: Both singlegroup, pre-post and crossover design studies published in any language before March 15, 2019 were included. Assessments of physical performance were accepted for analysis. study appraisal: The methodological quality of the included studies was assessed using 'QualSyst'. Of 18 selected articles, 16 were generally of strong quality and the remaining studies (n=2) were rated as moderate, although most lacked significant details about the Ramadan fasting. Most studies showed that Ramadan fasting did not impair short-term maximal performances in soccer players (i.e., vertical jump, sprint performance, maximal voluntary contraction, hand grip, agility performance). During the 30-s Wingate test, the repeated sprint exercise (RSE) tasks, and the long-duration incremental and non-incremental exercises, most studies reported some negative effects of Ramadan fasting even when the training load was maintained. For the soccer specific skills and test with ball, most studies reported that there was no significant negative effects of the fasting month on performance when the training load was maintained or slightly reduced during the Ramadan. The continuance of training during Ramadan fasting, with maintained training load, has no negative effects on short-term maximal performances and soccer specific skills and test with ball. However, performances of the 30-s Wingate test, the RSE tasks, and the long-duration incremental and non-incremental exercises were significantly impaired during Ramadan fasting even when the training load was maintained.





Latest research in football - week 45 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Improvements in strength and functional performance after Kinesio taping in semi-professional male soccer players with and without functional ankle instability
Reference: Foot (Edinb). 2019 Jun 27;41:12-18. doi: 10.1016/j.foot.2019.06.006. [Epub ahead of print]
Authors: Fereydounnia S, Shadmehr A, Attarbashi Moghadam B, Talebian Moghadam S, Mir SM, Salemi S, Pourkazemi F
Summary: The objectives of this study were to compare the immediate effects of two methods of Kinesio taping on muscle strength, functional performance, and balance in athletes with and without functional ankle instability (FAI). The present study investigated the effects of distal taping (muscle application over peroneus longus) and proximal- distal taping (muscle application over gluteus medius and peroneus longus) on the strength of evertor and hip abductor muscles, side hop test, figure of 8 hop test, and star excursion balance test in semi-professional male soccer players with and without FAI (n=15 in each group). A Multifactorial repeated measure ANOVA was used for comparison. There were significant differences for factor effect in all outcome measures (P<0.05), except for the figure of 8 hop test. No significant differences for group effects and group by factor interaction effects (P>0.05) was observed except for the side hop test. Kinesio taping had immediate effects on improving strength, performance and balance. However, there were no differences on the method of application. Clinicians can consider the application Kinesio taping during the rehabilitation process of athletes with FAI, to improve balance and strength. The long-term impacts of taping on the functional, balance and strength measures should be investigated in future studies.

#2 Hip Range of Motion: Which Plane of Motion Is More Predictive of Lower Extremity Injury in Elite Soccer Players? A Prospective Study
Reference: J Surg Orthop Adv. 2019 Fall;28(3):201-208.
Authors: Shah SS, Testa EJ, Gammal I, Sullivan J, Gerland RW, Goldstein J, Sheridan B, Mashura M, Shah AS, Goodwillie A, Cohn RM
Summary: The objective of this study was to determine which plane of hip motion (rotational or sagittal) is more predictive of lower extremity (LE) injury in elite soccer players. A total of 69 athletes (43 professional and 26 collegiate) were examined (mean age, 22.6 years). Bilateral hip internal rotation (IR), external rotation, extension, and flexion measurements were taken along with the modified Thomas test during preseason physicals. There were 42 LE injuries (injury rate 3.74/1000 athlete exposures). Mean IR was 25.2. and 29.9° for injured versus noninjured extremities, respectively (p = .009). There was a significant association between decreased IR (categorized as IR < 28°) and incidence of ipsilateral LE injury (p = .042). Extremities with IR < 28° were 2.81 times more likely to sustain a LE injury (95% CI,; p = .023). With a utilitarian focus, the current study has identified a measurement of decreased hip IR with potential for substantial clinical value in collegiate and professional soccer players. (Journal of Surgical Orthopaedic Advances 28(3):201-208, 2019).

#3 Italian consensus statement (2020) on return to play after lower limb muscle injury in football (soccer)
Reference: BMJ Open Sport Exerc Med. 2019 Oct 15;5(1):e000505. doi: 10.1136/bmjsem-2018-000505. eCollection 2019.
Authors: Bisciotti GN, Volpi P, Alberti G, Aprato A, Artina M, Auci A, Bait C, Belli A, Bellistri G, Bettinsoli P, Bisciotti A, Bisciotti A, Bona S, Bresciani M, Bruzzone A, Buda R, Buffoli M, Callini M, Canata G, Cardinali D, Cassaghi G, Castagnetti L, Clerici S, Corradini B, Corsini A, D'Agostino C, Dellasette E, Di Pietto F, Enrica D, Eirale C, Foglia A, Franceschi F, Frizziero A, Galbiati A, Giammatei C, Landreau P, Mazzola C, Moretti B, Muratore M, Nanni G, Niccolai R, Orizio C, Pantalone A, Parra F, Pasta G, Patroni P, Pelella D, Pulici L, Quaglia A, Respizzi S, Ricciotti L, Rispoli A, Rosa F, Rossato A, Sannicandro I, Sprenger C, Tarantola C, Tenconi FG, Tognini G, Tosi F, Trinchese GF, Vago P, Zappia M, Vuckovich Z, Zini R, Trainini M, Chamari K
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Summary: Return to play (RTP) decisions in football are currently based on expert opinion. No consensus guideline has been published to demonstrate an evidence-based decision-making process in football (soccer). Our aim was to provide a framework for evidence-based decision-making in RTP following lower limb muscle injuries sustained in football. A 1-day consensus meeting was held in Milan, on 31 August 2018, involving 66 national and international experts from various academic backgrounds. A narrative review of the current evidence for RTP decision-making in football was provided to delegates. Assembled experts came to a consensus on the best practice for managing RTP following lower limb muscle injuries via the Delphi process. Consensus was reached on (1) the definitions of 'return to training' and 'return to play' in football. We agreed on 'return to training' and RTP in football, the appropriate use of clinical and imaging assessments, and laboratory and field tests for return to training following lower limb muscle injury, and identified objective criteria for RTP based on global positioning system technology. Level of evidence IV, grade of recommendation D.

#4 Physical Performance Differences Between Starter and Non-Starter Players During Professional Soccer Friendly Matches
Reference: J Hum Kinet. 2019 Oct 18;69:283-291. doi: 10.2478/hukin-2019-0018. eCollection 2019 Oct.
Authors: Giménez JV, Leicht AS, Gomez MA
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Summary: The aim of this study was to investigate the physical performance differences between players that started (i.e. starters, ≥65 minutes played) and those that were substituted into (i.e. non-starter) soccer friendly matches. Fourteen professional players (age: 23.2 ± 2.7 years, body height: 178 ± 6 cm, body mass: 73.2 ± 6.9 kg) took part in this study. Twenty, physical performance-related match variables (e.g. distance covered at different intensities, accelerations and decelerations, player load, maximal running speed, exertion index, work-to-rest ratio and rating of perceived exertion) were collected during two matches. Results were analysed using effect sizes (ES) and magnitude based inferences. Compared to starters, non-starters covered greater match distance within the following intensity categories: >3.3≤4.2m/s (very likely), >4.2≤5 m/s (likely) and >5≤6.9 m/s (likely). In contrast, similar match average acceleration and deceleration values were identified for starters and non-starters (trivial). Indicators of workloads including player loads (very likely), the exertion index (very likely), and the work-to-rest ratio (very likely) were greater, while self- reported ratings of perceived exertion were lower (likely) for non-starters compared to starters. The current study demonstrates that substantial physical performance differences during friendly soccer matches exist between starters and non-starters. Identification of these differences enables coaches and analysts to potentially prescribe optimal training loads and microcycles based upon player's match starting status.

#5 Player Load and Metabolic Power Dynamics as Load Quantifiers in Soccer
Reference: J Hum Kinet. 2019 Oct 18;69:259-269. doi: 10.2478/hukin-2018-0072. eCollection 2019 Oct.
Authors: Reche-Soto P, Cardona-Nieto D, Diaz-Suarez A, Bastida-Castillo A, Gomez-Carmona C, Garcia-Rubio J, Pino-Ortega J
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Summary: There has recently been an increase in quantification and objective analysis of soccer performance due to improvements in technology using load indexes such as Player Load (PL) and Metabolic Power (MP). The objectives of this study were: (1) to describe the performance of PL and MP in competition according to the specific role, match-to- match variation, periods of play, game location and match status according to game periods, and (2) to analyze the relationship between both indexes. Twenty-one national-level soccer players were distributed in the following specific positional roles: external defenders (ED) (n = 4), central defenders (CD) (n = 4), midfielders (M) (n = 5), external midfielders (EM) (n = 4) and attackers (A) (n = 4). A total of 12 matches played by a Spanish Third Division team during the 2016/2017 season were analyzed. WIMU PROTM inertial devices (RealTrack System, Almeria, Spain) were used for recording the data. The main results were: (1) a performance reduction in both variables over the course of match time, (2) significant differences in both variables based on the specific position, (3) differences in physical demands during the season matches, (4) winning during a game period and the condition of being the visitor team provoked higher demands, and (5) a high correlation between both variables in soccer. In conclusion, different contextual variables influence the external load demands; both indexes are related so they could be used for external load quantification, and it is necessary to analyze physical demands of the competition for a specific and individualized load design in training sessions.

#6 Combined Small-Sided Game and High-Intensity Interval Training in Soccer Players: The Effect of Exercise Order
Reference: J Hum Kinet. 2019 Oct 18;69:249-257. doi: 10.2478/hukin-2018-0092. eCollection 2019 Oct.
Authors: Rabbani A, Clemente FM, Kargarfard M, Jahangiri S
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Summary: The aim of the present study was to compare combined small-sided game (SSG) and high-intensity interval training (HIT) with different order. Twenty-one semi-professional soccer players were divided into two groups: SSG+HIT (n = 10) and HIT+SSG (n = 11), and underwent similar four-week training programs. Players completed the 30-15 Intermittent Fitness Test (30-15IFT) before and after the experiment; maximum speed (VIFT) was recorded. During the experiment, seven sessions of SSG (3 vs 3) and HIT (15"-15" with 95-100% VIFT) were implemented. Weekly accumulated training loads for both groups during the experiment were similar. Moderate improvements in VIFT were observed in both SSG+HIT (+6.2%, 90% confidence limits, [CL] 4.6; 7.7 and Effect Size, [ES] +0.96) and HIT+SSG (+6.9%, 90% CL 4.6; 9.3 and ES +0.97) groups. Between-group difference in changes of VIFT was trivial (+0.7%, 90% CL -1.8; 3.3 and ES +0.11). Combining SSG and HIT in different order elicited the same enhancement in high-intensity intermittent performance in soccer players.

#7 Trends of Goal Scoring Patterns in Soccer: A Retrospective Analysis of Five Successive FIFA World Cup Tournaments
Reference: J Hum Kinet. 2019 Oct 18;69:231-238. doi: 10.2478/hukin-2019-0015. eCollection 2019 Oct.
Authors: Kubayi A, Toriola A
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Summary: This study analysed the 795 goals scored during a total of 320 matches played in five successive FIFA World Cup tournaments (1998-2014). Data were obtained through YouTube videos and analysed by means of Longomatch software. The variables analysed included the number of goals scored per half (45-min period), per 15-min period, and per 30-min period of extra time, goal scoring zones, goals scored by substitutes, types of goals scored, and goals scored according to the playing position. With regard to 15-min period analysis, most goals were scored between the 76th and 90th minutes (24.7%) of the game in all five World Cup competitions. Chi-square analyses showed no significant (p > 0.05) differences in the frequency of goal scoring patterns per 45-min and 15-min periods in the five World Cup tournaments. Most goals were scored from inside the goal (23.8%) and penalty (14.6%) areas. The greatest number of goals was scored by strikers (54.2%), followed by midfielders (33.3%) and defenders (2.3%). These findings provide practical implications for improving goal-scoring performance in soccer.

#8 Variability of Technical Actions During Small-Sided Games in Young Soccer Players
Reference: J Hum Kinet. 2019 Oct 18;69:201-212. doi: 10.2478/hukin-2019-0013. eCollection 2019 Oct.
Authors: Clemente FM, Sarmento H, Costa IT, Enes AR, Lima R
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Summary: The purpose of this study was three-fold: (i) to test the between-sessions variability of 3 vs. 3 and 6 vs. 6 formats in under-11 players, (ii) to assess the within-session variability of 3 vs. 3 and 6 vs. 6 formats, and (iii) to investigate the variations of technical actions between formats. Sixteen soccer players (10.1 ± 0.3 years old) participated in this study. Both formats of play were played twice within an interval of one week to test the between-session variability and the variables of conquered balls (CBs), received balls (RBs), lost balls (LBs), attacking balls/passes (ABs) and shots (Ss) were analyzed using the Performance Assessment in Team Sports instrument in all matches. Moderate variations on the sum of sets during the 3 vs. 3 and 6 vs. 6 formats were observed in all variables. Considering the variations of technical actions made between sets in the 3 vs. 3 format, likely moderate increases were found in set 2 vs. 1 in terms of RB (37.5%, [-2.7;94.2]), and likely small decreases were found in set 3 vs. 2 for the same variable (-18.3%, [-37.8;7.3]). In the 6 vs. 6 format, only possibly small increases were found for set 3 vs. 1 in S (22.5%, [-7.0;61.3]). Generally (sum of sets), the variables standardized per minute revealed almost certain very large decreases in the 6 vs. 6 vs. the 3 vs. 3 format in the variables of CB (-67.9%, [-75.3;-55.9]), LB (-66.0%, [-73.9;-55.7]), RB (-65.6%, [-74.8;- 53.1]) and S (-87.6%, [-93.1;-77.7]). The results of this study suggest that both formats of play are too noisy to be reproducible. The 3 vs. 3 format largely increased the number of individual technical actions.

#9 Analysis of Successful Offensive Play Patterns by the Spanish Soccer Team
Authors: Amatria M, Maneiro R, Anguera MT
Reference: J Hum Kinet. 2019 Oct 18;69:191-200. doi: 10.2478/hukin-2019-0011. eCollection 2019 Oct.
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Summary: Victory is the ultimate aim in soccer and therefore when a team wins an elite European or world championship, attempts will invariably be made to emulate the winning team's style of play. In this study, we performed an in-depth analysis of play by the Spanish soccer team during the 2012 UEFA European Championship, where it was crowned champion. Using observational methodology and T-pattern analysis, we identified hidden patterns of play that ended in a goal for the Spanish team. A generalizability coefficient (e2) of 0.986 demonstrated that the offensive patterns detected are robust and highly generalizable. These patterns were formed by technical actions consisting of ball control and pass, with alternations between short and long passes, in the central area of the rival pitch, with use of both wings to achieve width of play and prioritization of width over depth of play. We also found patterns showing that goals and shots at goal were made on a ball delivered from the opposite direction to the shot and were not preceded by a technical action.

#10 Practical Use of the Navigate Pain Application for the Assessment of the Area, Location, and Frequency of the Pain Location in Young Soccer Goalkeepers
Reference: J Hum Kinet. 2019 Oct 18;69:125-135. doi: 10.2478/hukin-2019-0091. eCollection 2019 Oct.
Authors: Muracki J, Kumorek M, Kisilewicz A, Pożarowszczyk B, Larsen DB, Kawczyński A, Boudreau S
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Summary: Next to winning, minimizing injuries during training and matches is one of the primary goals of professional team sports games. Soreness and pain can be early indicators and risk factors for acute or long-term injuries. Monitoring pain intensity and duration, as well as potential sources, are useful for planning practices and can be effective means for preventing injury. The aim of this study was to assess the areas and locations of pain in young soccer goalkeepers during a training camp, and to differentiate the area and frequency between pain arising from the muscles (MP), joints (JP), or as a result of an impact (IP). Recordings of the MP, JP, and IP location along with the area were performed using digital body mapping software (Navigate Pain Android app, Aalborg University, Denmark) installed on a tablet personal computer at the end of each training day across a 5-day training camp. There was a significant difference in the area between the three types of pain (p < 0.001). The post hoc analysis revealed statistically significant differences between the pixel areas of IP versus JP (p < 0.001), IP versus MP (p < 0.001), and JP versus MP (p < 0.001). There was no significant time-effect for the IP area between 1-5 days of training (p = 0.610), neither for MP (p = 0.118) or JP (p = 0.797) and no significant difference for all three pain areas between the front and the back side of the body. The body regions most often reported for MP were thighs, while for JP they were groin and hips, and for IP the hips, shoulders, and forearms were most frequently indicated. This is the first study to map and report the pain distribution associated with training across a 5-day training camp in soccer goalkeepers, and these findings emphasize the value of using digital pain drawings clinically as well as for monitoring the health status of soccer players.

#11 Relationships between the Expression of the ACTN3 Gene and Explosive Power of Soccer Players
Reference: J Hum Kinet. 2019 Oct 18;69:79-87. doi: 10.2478/hukin-2019-0020. eCollection 2019 Oct.
Authors: Domańska-Senderowska D, Szmigielska P, Snochowska A, Jastrzębski Z, Jegier A, Kiszałkiewicz J, Jastrzębska J, Pastuszak-Lewandoska D, Cięszczyk P, Suchanecka A, Wilk M, Brzeziański M, Brzeziańska-Lasota E
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Summary: Muscle strength and maximal speed are factors determining athlete's results during competition. Their association with ACTN3 gene activity has been documented. The purpose of this study was the analysis of ACTN3 gene expression during a 2 month training cycle of soccer players and its correlation with the countermovement jump (CMJ) and squat jump (SJ). The study group consisted of 22 soccer players (aged 17-18). The study material included peripheral blood lymphocytes. The relative expression (RQ) of the ACTN3 gene was analyzed by qPCR and performed before and after the two-month training cycle. Before the training cycle low expression levels of ACTN3 (median RQ = 0.95) were observed, yet after the training cycle they were elevated (median RQ = 1.98) ( p = 0.003). There was an increase in performance of both jumps: SJ (p = 0.020) and CMJ (p = 0.012) at the end of the training cycle. A simultaneous increase in the ACTN3 gene expression level and height in both jump tests was observed in 73% of athletes (p > 0.05). There were no significant relationships between the ACTN3 gene expression level and the results of the CMJ and SJ. However, explosive strength is a complex feature shaped by many different factors and it could be the reason why we did not observe correlations between these variables.

#12 Correlations between body composition, aerobic capacity, speed and distance covered among professional soccer players during official matches
Reference: J Sports Med Phys Fitness. 2019 Oct 24. doi: 10.23736/S0022-4707.19.09979-1. [Epub ahead of print]
Authors: Radzimiński Ł, Szwarc A, Padrón-Cabo A, Jastrzębski Z
Summary: The importance of sprinting and high-speed running activities during a soccer match is indisputable. The main purpose of this study was to investigate the relations between the players' speed, aerobic capacity, body composition and distance covered in different speed zones during official soccer matches and to compare the match performance variables according to playing position. Twenty-three professional soccer players (age: 27.9 ± 4.58 y, body mass: 78.8 ± 7.35 kg, height: 181.7 ± 6.53 cm) participated in this study. During 13 weeks of the competitive season, players participated in 16 official matches and completed body composition analyses, sprint tests, multistage shuttle run tests (MST), and incremental running tests (IRTs). Significant negative correlations were found between sprint distance and percent of fat mass (FM; r = -0.57, p < 0.0001), MST (r = 0.45, p < 0.001), maximal speed (r = 0.44, p < 0.001). High-speed running (HSR) distance covered by the players during the matches was significantly correlated with FM (r = -0.38, p < 0.001) and MST distance (r = 0.30, p < 0.01). These data indicate that professional soccer players with lower fat content and higher levels of aerobic capacity are able to cover longer distances in sprinting and HSR during official matches.

#13 Knee muscle and tendon stiffness in professional soccer players: a shear-wave elastography study
Reference: J Sports Med Phys Fitness. 2019 Oct 24. doi: 10.23736/S0022-4707.19.09938-9. [Epub ahead of print]
Authors: Taş S, Özkan Ö, Karaçoban L, Dönmez G, Çetin A, Korkusuz F
Summary: It is well known that several risk factors such as fatigue, previous injury, muscle strength deficit or imbalance are related to a higher incidence of knee injuries in professional soccer players. Knee muscle and tendon stiffness may be another factor that is related to knee injuries in professional soccer players. Therefore, the aim of the present study was to investigate the differences between professional soccer players and healthy sedentary males in terms of the stiffness of patellar tendon (PT), quadriceps tendon (QT), and rectus femoris muscle (RF) and vastus medialis muscle (VM). The study group was comprised of 17 professional male soccer players in age range of 24-37 years. The control group was comprised of 22 healthy sedentary males in an age range of 21-36 years. Shear-Wave Velocity (SWV) measurements of the selected muscles and tendons were performed using an ultrasonography device with a lineal probe. The professional soccer players had lower SWV of PT (p=0.024) and QT (p<0.001) in the dominant leg compared to the control group; however, SWV of PT (p=0.455) and QT (p=0.827) in the non-dominant leg were similar in both groups. SWV of RF was higher in both dominant and non-dominant legs in professional soccer players compared to the control group (p<0.05); however, SWV of VM was similar in both groups (p>0.05). Professional soccer players had lower PT and QT stiffness. On the other hand, they had higher RF stiffness compared to sedentary individuals. Furthermore, VM stiffness was similar in both groups.





Latest research in football - week 44 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Effect of the FIFA 11+ on Landing Patterns and Baseline Movement Errors in Elite Male Youth Soccer Players
Reference: J Sport Rehabil. 2019 Oct 18:1-8. doi: 10.1123/jsr.2018-0374. [Epub ahead of print]
Authors: Akbari H, Sahebozamani M, Daneshjoo A, Amiri-Khorasani M, Shimokochi Y.
Summary: There is no evidence regarding the effect of the FIFA 11+ on landing kinematics in male soccer players, and few studies exist regarding the evaluating progress of interventions based on the initial biomechanical profile. The aim was to investigate the effect of the FIFA 11+ program on landing patterns in soccer players classified as at low or high risk for noncontact anterior cruciate ligament injuries. Field-based functional movement screening performed at the soccer field was measured in a total of 24 elite male youth soccer players participated in this study. The intervention group performed the FIFA 11+ program 3 times per week for 8 weeks, whereas the control group performed their regular warm-up.Before and after the intervention, all participants were assessed for landing mechanics using the Landing Error Scoring System. Pretraining Landing Error Scoring System scores were used to determine risk groups. The FIFA 11+ group had greater improvement than the control group in terms of improving the landing pattern; there was a significant intergroup difference (F1,20 = 28.86, P < .001, ηp2=.591). Soccer players categorized as being at high risk displayed greater improvement from the FIFA 11+ program than those at low risk (P = .03). However, there was no significant difference in the proportion of risk category following the routine warm-up program (P = 1.000). The present study provides evidence of the usefulness of the FIFA 11+ program for reducing risk factors associated with noncontact anterior cruciate ligament injuries. The authors' results also suggest that soccer players with the higher risk profile would benefit more than those with lower risk profiles and that targeting them may improve the efficacy of the FIFA 11+ program.

#2 Neurodegenerative Disease Mortality among Former Professional Soccer Players
Reference: N Engl J Med. 2019 Oct 21. doi: 10.1056/NEJMoa1908483. [Epub ahead of print]
Authors: Mackay DF, Russell ER, Stewart K, MacLean JA, Pell JP, Stewart W
Summary: Neurodegenerative disorders have been reported in elite athletes who participated in contact sports. The incidence of neurodegenerative disease among former professional soccer players has not been well characterized. We conducted a retrospective cohort study to compare mortality from neurodegenerative disease among 7676 former professional soccer players (identified from databases of Scottish players) with that among 23,028 controls from the general population who were matched to the players on the basis of sex, age, and degree of social deprivation. Causes of death were determined from death certificates. Data on medications dispensed for the treatment of dementia in the two cohorts were also compared. Prescription information was obtained from the national Prescribing Information System. Over a median of 18 years, 1180 former soccer players (15.4%) and 3807 controls (16.5%) died. All-cause mortality was lower among former players than among controls up to the age of 70 years and was higher thereafter. Mortality from ischemic heart disease was lower among former players than among controls (hazard ratio, 0.80; 95% confidence interval [CI], 0.66 to 0.97; P = 0.02), as was mortality from lung cancer (hazard ratio, 0.53; 95% CI, 0.40 to 0.70; P<0.001). Mortality with neurodegenerative disease listed as the primary cause was 1.7% among former soccer players and 0.5% among controls (subhazard ratio [the hazard ratio adjusted for competing risks of death from ischemic heart disease and death from any cancer], 3.45; 95% CI, 2.11 to 5.62; P<0.001). Among former players, mortality with neurodegenerative disease listed as the primary or a contributory cause on the death certificate varied according to disease subtype and was highest among those with Alzheimer's disease (hazard ratio [former players vs. controls], 5.07; 95% CI, 2.92 to 8.82; P<0.001) and lowest among those with Parkinson's disease (hazard ratio, 2.15; 95% CI, 1.17 to 3.96; P = 0.01). Dementia-related medications were prescribed more frequently to former players than to controls (odds ratio, 4.90; 95% CI, 3.81 to 6.31; P<0.001). Mortality with neurodegenerative disease listed as the primary or a contributory cause did not differ significantly between goalkeepers and outfield players (hazard ratio, 0.73; 95% CI, 0.43 to 1.24; P = 0.24), but dementia-related medications were prescribed less frequently to goalkeepers (odds ratio, 0.41; 95% CI, 0.19 to 0.89; P = 0.02). In this retrospective epidemiologic analysis, mortality from neurodegenerative disease was higher and mortality from other common diseases lower among former Scottish professional soccer players than among matched controls. Dementia-related medications were prescribed more frequently to former players than to controls. These observations need to be confirmed in prospective matched-cohort studies. (Funded by the Football Association and Professional Footballers' Association.).

#3 Sport Specialization and Coordination Differences in Multisport Adolescent Female Basketball, Soccer, and Volleyball Athletes
Reference: J Athl Train. 2019 Oct;54(10):1105-1114. doi: 10.4085/1062-6050-407-18.
Authors: DiCesare CA, Montalvo A, Foss KDB, Thomas SM, Hewett TE, Jayanthi NA, Myer GD
Summary: Early sport specialization, or the participation in 1 sport year-round to the exclusion of all others, is a growing concern in youth athletics because of its possible association with musculoskeletal injury. The underlying injury risk may be the result of coordination differences that sport-specialized athletes have been speculated to exhibit relative to multisport athletes; however, little evidence exists to support or refute this notion. The aim was to examine relative hip- and knee-joint angular-motion variability among adolescent sport-specialized and multisport female adolescent athletes to determine how sport specialization may affect coordination. A total of 366 sport-specialized and 366 multisport adolescent female basketball, soccer, and volleyball players participated in this study with an drop-vertical-jump (DVJ) assessment. Average coupling-angle variability (CAV) for hip flexion and knee flexion, knee flexion and ankle flexion, hip flexion and knee abduction, knee flexion and knee abduction, knee flexion and knee internal rotation, and knee abduction and knee internal rotation. The sport-specialized group exhibited increased coupling variability in dominant-limb hip flexion and knee flexion (P = .015), knee flexion and knee abduction (P = .014), and knee flexion and knee internal rotation (P = .048) while landing during the DVJ, although they had small effect sizes (η2 = 0.010, 0.010, and 0.007, respectively). No differences were present between groups for any of the other CAV measures of the dominant limb, and no differences were found for any CAV measures of the nondominant limb (all P values > .05). Sport specialization was associated with increased variability of critical hip- and knee-joint couplings responsible for effective landing during the DVJ. Altered coordination strategies that involve the hip and knee joints may underlie unstable landings, inefficient force-absorption strategies, or greater contact forces that can place the lower extremities at risk for injury (or a combination of these).

#4 Evaluation for the effects of nutritional education on Chinese elite male young soccer players: The application of adjusted dietary balance index (DBI)
Reference: J Exerc Sci Fit. 2020 Jan;18(1):1-6. doi: 10.1016/j.jesf.2019.08.004. Epub 2019 Aug 20.
Authors: Zeng D, Fang ZL, Qin L, Yu AQ, Ren YB, Xue BY, Zhou X, Gao ZY, Ding M, An N, Wang QR
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Summary: The aim of this study was to evaluate the effect of nutrition education on Chinese elite male young soccer players through the knowledge, attitude, behavior (KAP) survey and an adjusted dietary balance index (DBI). 30 Chinese elite male young soccer players were randomly divided into two groups: lecture group (N = 15, Age: 16.7 ± 1.8 years, Height: 173.9 ± 9.0 cm; Weight: 62.4 ± 13.0 kg; Training years: 5.6 ± 2.7 years) and non-lecture group (N = 15, Age: 16.8 ± 1.7 years, Height: 175.5 ± 7.9 cm; Weight: 62.5 ± 12.3 kg; Training years: 6.2 ± 3.3). The comics book was given to the non-lecture group, while the a four-week nutritional quality education along with comic books were given to the lecture group. Before and after 4 weeks nutritional education, dietary nutritional status of both groups was assessed. The main outcome measurements included the scores for each part of the KAP survey, diet status (food-weighing method) and the dietary index in the adjusted DBI-07 system (DBI-low bound score, LBS; DBI-high bound score, HBS; and DBI-diet quality distance, DQD). In the lecture group, significant differences were found in the scores of general nutrition knowledge, sports nutrition knowledge and total scores of KAP dietary questionnaire after 4 weeks nutritional education (P < 0.01). However, there is no significant difference in dietary attitude and dietary behavior (P > 0.05) on both two groups. There is no significant change in the DBI-low bound score (LBS), DBI-high bound score (HBS) and DBI-diet quality distance (DQD) of dietary quality index (P > 0.05) in both two groups. Four weeks nutritional quality education improved the understanding of dietary nutrition among Chinese elite male young soccer players.

#5 Analysis of the Association between Running Performance and Game Performance Indicators in Professional Soccer Players
Reference: Int J Environ Res Public Health. 2019 Oct 21;16(20). pii: E4032. doi: 10.3390/ijerph16204032.
Authors: Modric T, Versic S, Sekulic D, Liposek S
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Summary: Running performance (RP) and game performance indicators (GPI) are important determinants of success in soccer (football), but there is an evident lack of knowledge about the possible associations between RP and GPI. This study aimed to identify associations between RP and GPI in professional soccer players and to compare RP and GPI among soccer playing positions. One hundred one match performances were observed over the course of half of a season at the highest level of national competition in Croatia. Players (mean ± SD, age: 23.85 ± 2.88 years; body height: 183.05 ± 8.88 cm; body mass: 78.69 ± 7.17 kg) were classified into five playing positions (central defenders (n = 26), full-backs (n = 24), central midfielders (n = 33), wide midfielders (n = 10), and forwards (n = 8). RP, as measured by global positioning system, included the total distance covered, distance covered in five speed categories (walking, jogging, running, high-speed running, and maximal sprinting), total number of accelerations, number of high-intensity accelerations, total number of decelerations, and number of high-intensity decelerations. The GPI were collected by the position-specific performance statistics index (InStat index). The average total distance was 10,298.4 ± 928.7 m, with central defenders having the shortest and central midfielders having the greatest covered distances. The running (r = 0.419, p = 0.03) and high-intensity accelerations (r = 0.493, p = 0.01) were correlated with the InStat index for central defenders. The number of decelerations of full-backs (r = -0.43, p = 0.04) and the distance covered during sprinting of forwards (r = 0.80, p = 0.02) were associated with their GPI obtained by InStat index. The specific correlations between RP and GPI should be considered during the conditioning process in soccer. The soccer training should follow the specific requirements of the playing positions established herein, which will allow players to meet the game demands and to perform successfully.

#6 Working memory capacity does not always promote dual-task motor performance: The case of juggling in soccer
Reference: Scand J Psychol. 2019 Oct 21. doi: 10.1111/sjop.12589. [Epub ahead of print]
Authors: Laurin R, Finez L
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Summary: The aim of this research was to refine our understanding of the role of working memory capacity (WMC) on motor performances that require attentional control in dual-task situations. Three studies were carried out on soccer players. Each participant had to perform a juggling task in both normal and dual-task conditions. In Study 1, the interfering task was a mental calculation test performed under time pressure (strong cognitive load). In Study 2, the interfering task was a count-down test (low cognitive load). In Study 3 an intra-individual design in which participants perform dual-tasks increasingly complex has been proposed. Results showed a positive relationship between participants' WMC and their dual-task motor performance when the cognitive load was low and a negative relationship when the cognitive load was high. This paper highlights the role of the WMC in the activation of different modes of processing and its importance on the performance in dual-task.

#7 Injury Profile of Elite Male Young Soccer Players in a Spanish Professional Soccer Club: A Prospective Study During 4 Consecutive Seasons
Reference: J Sport Rehabil. 2019 Oct 18:1-7. doi: 10.1123/jsr.2019-0113. [Epub ahead of print]
Authors: Raya-González J, Suárez-Arrones L, Navandar A, Balsalobre-Fernández C, Sáez de Villarreal E.
Summary: As the number of injuries in young soccer players increases, an epidemiological study is the first step in improving preventive strategies. The aim was to analyze the injury profile of a Spanish professional soccer club's academy during 4 consecutive seasons and to examine the injury incidence across different chronological age groups. Aggregate injury and exposure data collected during 4 consecutive seasons were collected of three hundred nine elite male young soccer players. Injuries that led to participation time missed from training and match play prospectively reported by medical or coaching staff of the club were used as outcome measures. A total of 464 time-loss injuries were observed during this study period. The overall injury incidence was 2.93 injuries per 1000 hours, with higher incidence during matches than during training (10.16 vs 2.10 injuries/1000 h; rate ratio [RR] = 0.21; 95% confidence interval [CI], 0.17-0.25; P < .05), with the U14 age group presenting the lowest injury rate (2.39 injuries/1000 h; RR = 1.15-1.57; P < .05). In terms of injury severity, moderate injuries were the most frequent (1.42 injuries/1000 h). Muscle injuries were the most common type of injuries (57.7%; 2.75 injuries/1000 h; RR = 1.84-13.4; P < .05), and hamstrings (93/268) were the most affected muscle group (0.58 injuries/1000 h; RR = 1.58-2.91; P < .05). Injury incidence showed a seasonal variation as indicated by peaks in August and October. In matches, specifically, the match period between 75 and 90 minutes showed the highest injury incidence (10.29 injuries/1000 h; RR = 1.89-6.38; P < .01). The findings of this study suggest that specific preventive strategies must be implemented to try to reduce the injury incidence in Spanish elite young soccer players attending to the characteristics of each age group.

#8 Elite Players' Perceptions of Football Playing Surfaces: A Qualitative Study
Reference: Res Q Exerc Sport. 2019 Oct 24:1-13. doi: 10.1080/02701367.2019.1660757. [Epub ahead of print]
Authors: Roberts JR, Osei-Owusu P, Mears AC, Harland AR
Summary: The decision by the International Football Association Board in 2004 to approve the use of artificial surfaces in elite football (soccer) competitions remains controversial amongst many players, managers and coaching staff. The aim of this study was to conduct a comprehensive assessment of players' opinions to better understand the influence of playing surfaces on the game of football and identify factors that may contribute to differences of opinion. Qualitative data were collected from 103 elite footballers and 21 coaching staff during a series of interviews and focus groups. A thematic analysis was conducted to identify patterns in the data. Players considered that the type and condition of a playing surface influenced ball-surface interactions, game play, tactics/strategy, footwear selection, movement, risk of injury and fatigue. Together these influence a player's perception of the suitability of a surface and also their mindset, which could ultimately affect their performance. The majority of participants in this study expressed a higher preference for natural grass over artificial turf pitches. A perceived increased risk of injury on artificial turf remains a primary concern despite a lack of supporting evidence in research studies. To address this discrepancy, the reporting of muscle soreness and the effect of constant surface switching merit further consideration. Not all participants shared the same views and player characteristics such as age, surface experience, injury history and playing style/position were found to be potential factors that could account for differences in elite players' opinions regarding the surfaces used in football.

#9 Acute effects of differential learning on football kicking performance and in countermovement jump
Reference: PLoS One. 2019 Oct 23;14(10):e0224280. doi: 10.1371/journal.pone.0224280. eCollection 2019.
Authors: Gaspar A, Santos S, Coutinho D, Gonçalves B, Sampaio J, Leite N
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Summary: The aim of this study was to identify the acute effects of a differential-learning training program on football kicking performance and countermovement jump. Twenty youth Portuguese under-15 football players participated in this study. All players were exposed to two training approaches: i) traditional, in which the players performed a total of 36 kicks in a blocked and repetitive approach; and ii) differential learning, which consisted in the 36 kicks using differential variations in each kick. Football kicking impact and velocity were assessed using a Stalker radar gun, while the kicking accuracy was assessed by aggregating the total number of points achieved during 12 kicks into a goal, which was divided into quantifiable scoring zones. Lastly, leg power was measured using a countermovement jump. Measurements were performed at baseline, post-intervention, and following a 35-minute training match. The comparisons between the baseline and post-test revealed that the differential learning approach promoted a possibly ~5% increase in the countermovement jump (small effects) and a likely ~3% increase in the average velocity (small effects) when compared with the traditional training approach. From the accuracy perspective, there was a moderate decrease from the baseline to the post-test and post-match in accurate kicks into zone 1 (centre of the goal) and a moderate decrease from the baseline to the post-match in accurate kicks into zone 5 (lateral zones at short height) in the differential intervention. In turn, a small increase in the accurate kicks into zones 4 and 6 (lateral zones of the goal and nearest to the bar, respectively) was found from the baseline to the post-match in the differential intervention. Overall, the differential learning intervention was more beneficial than a traditional training protocol with respect to acute improvements in countermovement jump performance, football kicking velocity and higher scoring zones kicking accuracy.

#10 Testing the functionality of peripheral vision in a mixed-methods football field study
Reference: J Sports Sci. 2019 Dec;37(24):2789-2797. doi: 10.1080/02640414.2019.1664100. Epub 2019 Sep 6.
Authors: Vater C, Luginbühl S, Magnaguagno L
Summary: In team sports, peripheral vision might be useful to simultaneously monitor movements of opponents and teammates. Until now, however, little is known about the perceptual-cognitive processes underlying peripheral vision in a sporting task. Therefore, we used a mixed-methods approach with in-situ decision making (3 vs. 3 situations) and retrospective verbal reports to identify perceptual strategies used for optimal information pick-up in high- and low-skilled football players. Our results show that the use of peripheral vision by central defenders depends on the position of the ball and the position of the direct opponent. Players were shown to either use a pivot strategy, whereby they frequently look at the direct opponent if he is not in the possession of the ball in addition to making saccades to monitor other players, or they employ a more direct strategy, in which gaze is anchored on this location, avoiding saccades and monitoring the other players with peripheral vision. Based on our findings we make recommendations about how these gaze strategies can be further tested in future research and how sports practice can benefit from these results.

#11 The Relationship Between Personality Traits and Muscle Injuries in Swedish Elite Male Football Players
Reference: J Sport Rehabil. 2019 Oct 18:1-6. doi: 10.1123/jsr.2018-0473. [Epub ahead of print]
Authors: Eckerman M, Svensson K, Edman G, Alricsson M.
Summary: The physical and mental demands of an elite football player are complex, which may explain why injuries are common in football. At elite level, muscle injuries of the lower-extremity are the most common among male football players, and the research hitherto is limited. The aim was to investigate whether personality traits affect the incidence of muscle injuries among male football players from the first league in Sweden. A male football team from the first league in Sweden was prospectively followed, in terms of muscle injuries of the lower-extremity during 8 seasons, between 2007 and 2015. All muscle injuries included in this study were evaluated and diagnosed with ultrasonography. Players from the team filled out the Swedish Universities Scales of Personality questionnaire. Swedish Universities Scales of Personality questionnaire consists of 91 items and is divided into 13 categories. The raw values of each scale were linearly transformed to T scores, having a mean (SD) of 50 (10). All variables were summarized with standard descriptive statistics, such as frequency, mean, and SD. As data were of interval scale and no variable distribution was severely skewed, differences between noninjured players, rarely injured players, and frequently injured players were analyzed with 1-way analysis of variance with post hoc tests by Tukey honestly significant difference test. No significant difference in personality traits were observed between noninjured players, rarely injured players, and frequently injured players regarding number of muscle injuries (P > .05). However, a trend (P = .07) was seen, where frequently injured players scored higher on stress susceptibility than rarely injured players. A player's stress susceptibility should be taken into consideration by the player, coaches, and medical staff when assessing the risk of a muscle injury. Also, preventive measures available for these players may need to be considered.





Latest research in football - week 43 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Acute sleep hygiene strategy improves objective sleep latency following a late-evening soccer-specific training session: A randomized controlled trial
Reference: J Sports Sci. 2019 Dec;37(23):2711-2719. doi: 10.1080/02640414.2019.1661938. Epub 2019 Sep 6.
Authors: Vitale JA, La Torre A, Banfi G, Bonato M
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Summary: The aim of this study was to evaluate the effects of sleep hygiene (SH) education on sleep quality in soccer players after a late-evening small-sided-game (SSG) training session. Twenty-nine non-professional players were recruited and allocated to either an experimental group (EG, n = 17) that received SH education, or a control group (CG, n = 12). SSG consisted of 3 × 4 min in a 4vs4, with 3 min of recovery and was performed at 8.00 p.m. Sleep quality was monitored via actigraphy and sleep diary entries before (PRE) and two nights after (POST1, POST2) the SSG. Sleep latency (SL) differed between the two groups at POST1 (4.9 ± 5.4 vs. 15.5 ± 16.1 for EG and CG, respectively; p = 0.017, effect size [ES] = 2.0); SL values were lower at POST1 compared to PRE for the EG (-47%; p = 0.021, ES = 0.6). Subjective sleep quality was better in the EG than the CG at POST1 (8.6 ± 1.0 vs. 7.1 ± 2.0 for EG and CG, respectively; p = 0.016, ES = 0.9) with a significant improvement over PRE-values (+11.0%, p = 0.004, ES = 0.8). Although SL and subjective sleep quality did not decrease significantly from POST1 to POST2 values at POST2 no longer differed significantly form baseline and, hence, indicate that observed effects may be short-lasting. No other objective sleep indices were influenced by late-evening training or SH practices implemented by the EG. Soccer players may benefit from acute SH strategies to reduce the time to sleep onset after late-evening training sessions.

#2 New curve sprint test for soccer players: Reliability and relationship with linear sprint
Reference: J Sports Sci. 2019 Oct 13:1-6. doi: 10.1080/02640414.2019.1677391. [Epub ahead of print]
Authors: Fílter A, Olivares J, Santalla A, Nakamura FY, Loturco I, Requena B
Summary: The speed performance is involved not only in linear sprints, but also in a wide spectrum of multi-directional movements, such as curve sprinting. Curved sprint can be defined as sprint with gradual and continuous change of direction (COD). Although ~85% of the actions performed at maximum velocity in a professional soccer league are curvilinear sprints, there is not any specific test to assess this ability. This study aimed to analyse the reliability of a new curve sprint test, and compare its results with those obtained by soccer players in linear sprint. Forty experienced soccer players performed 3 attempts of curve sprint (using the penalty arc) to right and left side (17 m), and 3 linear sprints (17 m) in two different days. The ICCs (inter-session reliability) were 0.93 for sprint curve right side (CSRS) and 0.89 for sprint curve left side (CSLS), considered "acceptable". The CVs (intra-session reliability) were 0.87% in CSRS and 1.15% in CSLS. The coefficient of determination (R2) between linear and curve sprinting was ~35%. The association between curve sides was "very large" (r = 0.878; p < 0.01). In summary, we showed that "curve sprint test" is highly reliable, and that curvilinear and linear sprints are different and independent actions.

#3 The most demanding passages of play in football competition: a comparison between halves
Reference: Biol Sport. 2019 Sep;36(3):233-240. doi: 10.5114/biolsport.2019.86005. Epub 2019 Jun 14.
Authors: Casamichana D, Castellano J, Diaz AG, Gabbett TJ, Martin-Garcia A
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Summary: The purpose of this investigation was to determine the differences between halves in the most demanding passages of play in football players according to playing position and duration-specific activity. Global positioning system data were collected from twenty-three football players from a reserve squad of the Spanish La Liga. A total of 265 individual match half data were analysed across the competitive season. Players were categorised based on positional groups: full-back (FB), central defender (CD), midfielder (MF), offensive midfielder (OMF) and forwards (FW). The most demanding passage of match play was analysed using a rolling average method, where maximal values were calculated for five different time durations (1, 3, 5, 10 min and half completed) using distance (m·min-1), high metabolic load distance (HMLD; m·min-1) and average metabolic power (AMP; W·kg-1) as variables of interest. The differences between the first and second half increased as the rolling duration increased, reaching the greatest difference between halves in the complete half (45 min) in all the variables studied (ES = 0.54 ± 0.15, 0.75 ± 0.15 and 0.76 ± 0.15 in distance, HMLD and AMP). The CDs were the players that presented the greatest differences, and it was in the AMP variable where the greatest differences between the first and second half were found. Large decreases in AMP were found for CD (ES = -1.30 ± 0.36) and moderate decreases were found in AMP for FB (ES = -0.84 ± 0.30) and OMF (ES = -0.78 ± 0.37). These results provide insight into the most demanding passages of play to inform training practices for specific football playing positions.

#4 A method for predicting background advertisement exposure parameters in sporting events: Televised football game approach
Reference: PLoS One. 2019 Oct 17;14(10):e0223662. doi: 10.1371/journal.pone.0223662. eCollection 2019.
Authors: Xiao Y, John C, Ren X, Zhang P
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Summary: The background advertisement exposure parameters (BAEP) forms a premise for sponsorship negotiation and the basis for estimating the sponsorship value of background advertising. Prediction of the BAEP has a great contribution to the sporting events organizers and sponsors in terms of negotiating, decision-making for bidding, and income-generating. Virtual Reality (VR), technology was utilized to construct a virtual three-dimensional model of the sports venue and simulate the telecast of the event. Based on VR technology and computer graphics theory, a pre-event prediction method for estimating the background advertisement exposure parameters of sporting events was put forward. The pre and post measures of the thirty BAEP of televised football games were compared to verify the effectiveness of the prediction method. There was no significant difference between the pre- and post-measurement results for the same football game. The pre- and post-measurement results of the thirty BAEP of televised football games were tightly matched. Using the prediction method can predict the BAEP of televised football games effectively and overcomes the shortcomings of current prediction methods that inhibits the effectiveness of the prediction of exposure parameters due to changes such as the type of the sporting events, the size of the sports venue, the layout of the background advertisements, and the placement of the television cameras, etc.

#5 Trait Self-Control Discriminates Between Youth Football Players Selected and Not Selected for the German Talent Program: A Bayesian Analysis
Reference: Front Psychol. 2019 Sep 26;10:2203. doi: 10.3389/fpsyg.2019.02203. eCollection 2019.
Authors: Wolff W, Bertrams A, Schüler J
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Summary: Trait self-control predicts success in various walks of life. Sports is a prototypical domain, where self-control is required, and there is evidence that successful athletes display superior self-control. Here, we assess if self-control already differs between athletes that were selected for a talent development program and non-selected athletes. Self-reported trait self-control was assessed in n = 25 (7 = female, 13.2 ± 1.7 years) youth football players who were part of the German talent development program and in n = 27 (6 = female, 13.6 ± 1.8 years) age and sex matched youth football players, who trained at the same clubs but had not been selected for the program. A one-sided Bayesian two-sample t-test yielded a Bayes factor of 54.99, indicating very strong evidence for the hypothesis that elite youth football players have higher trait self-control than non-elite youth football players. The 95% credibility interval indicates that the true value of δ lies between 0.28 and 1.42, indicating some uncertainty regarding the effects' magnitude. We show that already at young age, elite athletes display higher levels of self-control than their less successful peers. This underlines the importance of self-control as an important personality factor for success. These findings might have implications for talent selection and for sport psychological training.

#6 Clinical Features and isokinetic Parameters in Assessing Injury Risk in elite Football Players
Reference: Int J Sports Med. 2019 Oct 15. doi: 10.1055/a-1014-2911. [Epub ahead of print]
Authors: Liporaci RF, Saad M, Grossi DB, Riberto M
Summary: Football players frequently face the occurrence of non-contact injuries. Although there are likely multiple factors that contribute to increased risk of non-contact injury, it remains a challenge to correlate all these factors. However, it is not clear how much of individual training abilities may interfere in these events. As such, the primary aim of the present study was to determine whether the reduction of functional performance of the thigh in the isokinetic knee tests, anthropometric and morbid history can establish risk factors for lower-limb musculoskeletal injuries throughout the season. The incidence of injuries and odds ratios were calculated for suspected risk factors. Hamstring/Quadriceps conventional ratio outside of the safety range (55-64%) may be involved in the occurrence of non-contact muscle injuries and the risk for any musculoskeletal injuries in the lower extremities is 16 times higher when extensor peak of torque exceeds 10% and 12 times higher when flexor peak of torque difference was greater than 10%. This kind of evaluation can result in intervention programs that may decrease the risk of lower-limb musculoskeletal injuries. Based on these results we can establish a specific and individualized exercise program for each athlete and thus protect them during the season.

#7 Psychological characteristics of developing excellence in elite youth football players in English professional academies
Reference: J Sports Sci. 2019 Oct 13:1-7. doi: 10.1080/02640414.2019.1676526. [Epub ahead of print]
Authors: Saward C, Morris JG, Nevill ME, Minniti AM, Sunderland C
Summary: This mixed-longitudinal prospective study examined the development of psychological characteristics of developing excellence in relation to the career progression of elite youth football players. In a 20-month period, 111 academy football players aged 11-16 completed the Psychological Characteristics of Developing Excellence Questionnaire (PCDEQ) on 1-5 occasions. This combination of single and repeated assessments resulted in a mixed-longitudinal sample of 226 completed PCDEQs. Players were then prospectively tracked, and their scholarship status assessed at follow-up, at age U17. Multilevel modelling revealed that coping with performance and developmental pressures scores increased with age, and that Category 1-2 academy scholars (4.35 ± 0.61) scored higher than Category 3-4 academy scholars (3.99 ± 0.67) and non-scholars (4.02 ± 0.78) (p < .05). Evaluating performances and working on weaknesses scores increased with age for Category 1-2 academy scholars (U12-U14 vs. U15-U16 = 5.16 ± 0.48 vs. 5.38 ± 0.45), compared to non-scholars (U12-U14 vs. U15-U16 = 5.11 ± 0.59 vs. 5.03 ± 0.71) (p < .05). Imagery use during practice and competition scores decreased with age (U12-U14 vs. U15-U16 = 4.45 ± 0.66 vs. 4.29 ± 0.70) (p < .05). A blend of PCDEs may facilitate optimal career progression. Football academies should develop players' PCDEs, with a particular focus on developing their coping skills and their ability to realistically evaluate performances and work on weaknesses.

#8 How does the modern football goalkeeper train? - An exploration of expert goalkeeper coaches' skill training approaches
Reference: J Sports Sci. 2019 Jul 16:1-9. doi: 10.1080/02640414.2019.1643202. [Epub ahead of print]
Authors: Otte FW, Millar SK, Klatt S
Summary: The football goalkeeper position arguably represents a unique role within the team sport. Despite its highly complex skill demands, research on football goalkeeping has only sporadically examined the position within isolated and limited parameters. In particular, there is limited literature on "modern" skill acquisition training methods and approaches within the field of goalkeeper training. In a cross-cultural study with fifteen expert goalkeeper coaches, researchers here examined the overarching research question of "how does the modern football goalkeeper train?". Semi-structured interviews explored expert coaches' views on critical skills for performance in goalkeeping and the training approaches used to develop these critical skills. Results indicate that four skill sets are considered essential by goalkeeper coaches, these are: decision-making skills, athleticism, mentality, and technical skills. In terms of developing these skills in goalkeeper-specific training, the majority of expert coaches apply a similar microstructure to training sessions. This structure involves a steady progression from simple to complex training tasks, where for large parts, isolated technical training appears to be prioritised over a holistic training approach that integrates technical skills and perceptual-cognitive components (e.g., decision making). Scientific and practical recommendations for researchers and practitioners in the field of football goalkeeper coaching are provided.

#9 The effect of age on between-match physical performance variability in professional soccer players
Reference: Res Sports Med. 2019 Oct 20:1-9. doi: 10.1080/15438627.2019.1680985. [Epub ahead of print]
Authors: Lorenzo-Martínez M, Rey E, Padrón-Cabo A
Summary: This study aimed to analyse the effect of age on between-match variability of physical performance in professional soccer players. For this purpose, observations on entire match performance were collected on 787 professional soccer players competing in the first or second division of Spanish league during the 2017-2018 season. Players were classified into six groups according to their age: G1 (≤22.5 years), G2 (22.6-25.1 years), G3 (25.2-27.5 years), G4 (27.6-30.1 years), G5 (30.2-33.1 years) and G6 (≥33.2 years). Coefficients of variation (CVs) were calculated individually for each player and performance variable: total distance, low- intensity, medium-intensity, high-intensity running (HIR), sprinting, number of HIR, number of sprints, average speed and maximal speed. The main finding of this study was that players under 25.2 years (G1 and G2) showed lower CVs for high-intensity activities (HIR and sprinting) in comparison with players over 33.1 years (G6). These findings provide useful information for soccer coaches, who could put extra attention on physical performance of the oldest players when they have to play an entire match, because their performance is more variable and uncertain in comparison with the youngest.

#10 Basal Serum Cortisol and Testosterone/Cortisol Ratio Are Related to Rate of Na+ Lost During Exercise in Elite Soccer Players
Reference: Int J Sport Nutr Exerc Metab. 2019 Oct 17:1-6. doi: 10.1123/ijsnem.2019-0129. [Epub ahead of print]
Authors: Castro-Sepulveda M, Cancino J, Fernández-Verdejo R, Pérez-Luco C, Jannas-Vela S, Ramirez-Campillo R, Del Coso J, Zbinden-Foncea H
Summary: During exercise, the human body maintains optimal body temperature through thermoregulatory sweating, which implies the loss of water, sodium (Na+), and other electrolytes. Sweat rate and sweat Na+ concentration show high interindividual variability, even in individuals exercising under similar conditions. Testosterone and cortisol may regulate sweat Na+ loss by modifying the expression/activity of the cystic fibrosis transmembrane conductance regulator. This has not been tested. As a first approximation, the authors aimed to determine whether basal serum concentrations of testosterone or cortisol, or the testosterone/cortisol ratio relate to sweat Na+ loss during exercise. A total of 22 male elite soccer players participated in the study. Testosterone and cortisol were measured in blood samples before exercise (basal). Sweat samples were collected during a training session, and sweat Na+ concentration was determined. The basal serum concentrations of testosterone and cortisol and their ratio were (mean [SD]) 13.6 (3.3) pg/ml, 228.9 (41.4) ng/ml, and 0.06 (0.02), respectively. During exercise, the rate of Na+ loss was related to cortisol (r = .43; p < .05) and to the testosterone/cortisol ratio (r = -.46; p < .01), independently of the sweating rate. The results suggest that cortisol and the testosterone/cortisol ratio may influence Na+ loss during exercise. It is unknown whether this regulation depends on the cystic fibrosis transmembrane conductance regulator.

#11 Comparison of Drop Jump and Tuck Jump Knee Joint Kinematics in Elite Male Youth Soccer Players: Implications for Injury Risk Screening
Reference: J Sport Rehabil. 2019 Oct 18:1-6. doi: 10.1123/jsr.2019-0077. [Epub ahead of print]
Authors: Lloyd RS, Oliver JL, Myer GD, De Ste Croix MB, Wass J, Read PJ.
Summary: Despite the popularity of jump-landing tasks being used to identify injury risk factors, minimal data currently exist examining differences in knee kinematics during commonly used bilateral jumping tasks. This is especially the case for rebounding-based protocols involving young athletes. The aim was to compare the frontal plane projection angles (FPPAs) during the drop vertical jump (DVJ) and tuck jump assessment (TJA) in a cohort of elite male youth soccer players of varying maturity status. A total of 57 male youth soccer players from an English championship soccer club participated in this study. Participants performed 3 trials of the DVJ and TJA, during which movement was recorded with 2-dimensional video cameras. FPPA for both right (FPPA-r) and left (FPPA-l) legs, with values <180° indicative of medial knee displacement. On a whole-group level, FPPA-r (172.7° [7.4°] vs 177.2° [11.7°]; P < .05; effect size [ES] = 0.46) and FPPA-l (173.4° [7.3°] vs 179.2° [11.0°]; P < .05; ES = 0.62) were significantly greater for both limbs in the TJA compared with the DVJ; however, these differences were less consistent when grouped by maturity status. FPPA-r during the TJA was significantly and moderately greater in the circa-peak height velocity (PHV) group compared with the post-PHV cohorts (169.4° [6.4°] vs 175.3° [7.8°]; P < .05; ES = 0.49). Whole-group data showed moderate relationships for FPPA-r and FPPA-l between the TJA and DVJ; however, stronger relationships were shown in circa- and post-PHV players compared with the pre-PHV cohort. Considering that the TJA exposed players to a larger FPPA and was sensitive to between-group differences in FPPA-r, the TJA could be viewed as a more suitable screen for identifying FPPA in young male soccer players.





Latest research in football - week 42 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Return-to-Play Practices Following Hamstring Injury: A Worldwide Survey of 131 Premier League Football Teams
Reference: Sports Med. 2019 Oct 8. doi: 10.1007/s40279-019-01199-2. [Epub ahead of print]
Authors: Dunlop G, Ardern CL, Andersen TE, Lewin C, Dupont G, Ashworth B, O'Driscoll G, Rolls A, Brown S, McCall A
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Summary: Return-to-play (RTP) is an on-going challenge in professional football. Return-to-play related research is increasing. However, it is unknown to what extent the recommendations presented within research are being implemented by professional football teams, and where there are gaps between research and practice. The purposes of this study were (1) to determine if premier-league football teams worldwide follow a RTP continuum, (2) to identify RTP criteria used and (3) to understand how RTP decision-making occurs in applied practice. We sent a structured online survey to practitioners responsible for the RTP programme in 310 professional teams from 34 premier-leagues worldwide. The survey comprised four sections, based on hamstring muscle injury: (1) criteria used throughout RTP phases, (2) the frequency with which progression criteria were achieved, (3) RTP decision-making process and (4) challenges to decision-making. One-hundred and thirty-one teams responded with a completed survey (42%). One-hundred and twenty-four teams (95%) used a continuum to guide RTP, assessing a combination of clinical, functional and psychological criteria to inform decisions to progress. One-hundred and five (80%) teams reported using a shared decision-making approach considering the input of multiple stakeholders. Team hierarchy, match- and player-related factors were common challenges perceived to influence decision-making. General research recommendations for RTP and the beliefs and practices of practitioners appear to match with, the majority of teams assessing functional, clinical and psychological criteria throughout a RTP continuum to inform decision-making which is also shared among key stakeholders. However, specific criteria, metrics and thresholds used, and the specific involvement, dynamics and interactions of staff during decision-making are not clear.

#2 Match Running Performance on Three Different Competitive Standards in Norwegian Soccer
Reference: Sports Med Int Open. 2019 Oct 16;3(3):E82-E88. doi: 10.1055/a-0943-3682. eCollection 2019 Dec.
Authors: Sæterbakken A, Haug V, Fransson D, Grendstad HN, Gundersen HS, Moe VF, Ylvisaker E, Shaw M, Riiser A, Andersen V
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Summary: The aim of the study was to compare running performance of three competitive standards and to examine the effects of being promoted to a higher league in Norwegian football. One club's first and second team were included. The first team consisted of professional soccer players playing at Level 2 (2015 season) and Level 1 (2016 season). The second team consisted of amateurs playing at Level 4. A fully automatic tracking system was used to examine running performance, divided into different running-speed categories and playing position. Forty-one matches were included containing 278 observations. Level 1 performed 61 and 51% sprinting compared to Level 2 and Level 4 but similar high-speed running. Similar high-speed running distances were observed only for the different playing positions at Level 1 compared to Level 2 and 4. The sprinting distance was greater for the central defender and attacker, and the number of accelerations was greater for central midfielders and wide midfielders' playing at Level 1 compared to lower competitive standards. In conclusion, better competitive standards resulted in greater high-intensity actions than lower leagues in Norwegian soccer. Furthermore, only central defenders and attackers increased their high-intensity locomotions when the team was promoted.

#3 Effects of different repeated sprint-training frequencies in youth soccer players
Reference: Biol Sport. 2019 Sep;36(3):257-264. doi: 10.5114/biolsport.2019.87047. Epub 2019 Jul 31.
Authors: Rey E, Padrón-Cabo A, Costa PB, Lago-Fuentes C
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Summary: The aim of this study was to determine the effects of 2 different repeated-sprint ability (RSA) training frequencies (2 RSA sessions per week [RSA2D] or 1 RSA session [RSA1D]) under volume-equated conditions on sprint and RSA performance in under-15 (U15) soccer players. Twenty-seven youth male soccer players (age: 12.29±0.47 years; height: 158.35±10.86 cm; weight: 45.08±8.05 kg) were randomly assigned to RSA2D (n=14) or RSA1D (n=13) groups. The players performed the same RSA training for 6 weeks, and only the training frequency differed between the groups. Before and after the training period, 5 m sprint, 10 m sprint, 20 m sprint and the RSA test were assessed. No significant time × group interactions were observed (p>0.05). Within-group analysis showed significant improvements in 20 m sprint (p=0.046, partial eta squared [η p 2 ] = 0.150, large) and RSA average time (p=0.001, η p 2 =0.438, large), fastest time (p=0.012, η p 2 =0.229, large), and total time (p=0.001, η p 2 =0.438, large) from pre-test to post-test in RSA1D and RSA2D groups. However, no significant pre-post changes (p>0.05) were found in 5 m and 10 m sprint tests. In the between-group analysis, there were no significant differences between RSA1D and RSA2D groups in any variable. In conclusion, the current findings suggest that 6 weeks of RSA training 1 or 2 times per week in addition to typical soccer training produced significant and similar improvements in sprint and RSA performances. This information could be useful for coaches when planning training sessions during congested fixtures of soccer competitions or in periods when the emphasis should be placed on other physical qualities.

#4 Running technique is more effective than soccer-specific training for improving the sprint and agility performances with ball possession of prepubescent soccer players
Reference: Biol Sport. 2019 Sep;36(3):249-255. doi: 10.5114/biolsport.2019.87046. Epub 2019 Jul 31.
Authors: Lupo C, Ungureanu AN, Varalda M, Brustio PR
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Summary: Soccer-specific training is easily associable to players' sprint abilities demonstrated during a match. However, no clear evidence has been provided to show whether this approach is more effective than training focused on running techniques for sprints in prepubescent soccer players. Thus, the present study aimed at comparing the effects of these two training approaches on prepubescent soccer players' sprint performances. Ninety-five players (10±2 years) competing in local (Piedmont, Italy) Under-9 (N=21), -10 (N=24), -11 (N=25) and -13 (N=25) championships were recruited for the study. Sixty-three and 32 players were included in the running training group (RTG) and soccer-specific group (SSG), respectively. Before (PRE) and after (POST) the training period (2 weekly sessions for 12 weeks), sprint abilities were evaluated by means of four 20-m sprint tests: linear sprint (20-mL), linear sprint with ball possession (20-mLB), sprint with change of direction (20-mCoD), sprint with change of direction and with ball possession (20-mCoDB). A linear mixed model was applied to evaluate differences (P≤0.05) between the RTG and SSG in the four tests and categories, comparing PRE and POST performances. A main effect emerged for the interaction between groups, sessions (p=0.014; Between PRE ES range=0.03, 0.85; Within PRE-POST ES range=-0.45, 0.09), highlighting a POST improvement of RTG for the 20-mLB (Δ=-7.9%; ES=0.85) and 20-mCoDB (Δ=-5.9%; ES=0.33). In contrast, no improvements emerged for the SSG. The present findings indicate that the training approach of the RTG is more able to improve prepubescent soccer players' sprint performances than that of the SSG, with the emphasis on ball possession executions, which are particularly game-related.

#5 Effects of in-season enhanced negative work-based vs traditional weight training on change of direction and hamstrings-to-quadriceps ratio in soccer players
Reference: Biol Sport. 2019 Sep;36(3):241-248. doi: 10.5114/biolsport.2019.87045. Epub 2019 Jul 31.
Authors: Coratella G, Beato M, Cè E, Scurati R, Milanese C, Schena F, Esposito F
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Summary: The present study investigated the effects of in-season enhanced negative work-based training (ENT) vs weight training in the change of direction (COD), sprinting and jumping ability, muscle mass and strength in semi-professional soccer players. Forty male soccer players participated in the eight-week, 1 d/w intervention consisting of 48 squat repetitions for ENT using a flywheel device (inertia=0.11 kg·m -2 ) or weight training (80%1 RM) as a control group (CON). Agility T-test, 20+20 m shuttle, 10 m and 30 m sprint, squat jump (SJ) and countermovement jump (CMJ), lean mass, quadriceps and hamstrings strength and the hamstrings-to-quadriceps ratio were measured. Time on agility T-test and 20+20 m shuttle decreased in ENT (effect-size =-1.44, 95% CI -2.24/-0.68 and -0.75, -1.09/-0.42 respectively) but not in CON (-0.33, -0.87/0.19 and -0.13, -0.58/0.32). SJ and CMJ height increased in both ENT (0.71, 0.45/0.97 and 0.65, 0.38/0.93) and CON (0.41, 0.23/0.60 and 0.36, 0.12/0.70). Overall, quadriceps and hamstrings strength increased in both ENT and CON (0.38/0.79), but the hamstrings-to-quadriceps ratio increased in ENT (0.31, 0.22/0.40) but not in CON (0.03, -0.18/0.24). Lean mass increased in both ENT (0.41, 0.26/0.57) and CON (0.29, 0.14/0.44). The repeated negative actions performed in ENT may have led to improvements in braking ability, a key point in COD performance. Semi-professional soccer players may benefit from in-season ENT to enhance COD and the negative-specific adaptations in muscle strength and hamstrings-to-quadriceps ratio.

#6 Do asymmetry scores influence speed and power performance in elite female soccer players?
Reference: Biol Sport. 2019 Sep;36(3):209-216. doi: 10.5114/biolsport.2019.85454. Epub 2019 May 30.
Authors: Loturco I, Pereira LA, Kobal R, Abad CCC, Rosseti M, Carpes FP, Bishop C
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Summary: This study examined the relationships between vertical jump asymmetries and speed and power performance in elite female soccer athletes. Sixteen professional female soccer players (age: 23.0 ± 3.8 years; body mass: 60.2 ± 7.3 kg; height: 165.1 ± 5.5 cm) from the same professional club participated in this study. Athletes performed unilateral and bilateral squat jumps (SJ) and countermovement jumps (CMJ) on a portable force plate; 30-m sprinting test; Zigzag change-of-direction (COD) test; and muscle power testing using the jump squat (JS) exercise. Asymmetry scores were obtained from the results of the unilateral SJ and CMJ by the percentage difference between the dominant and non-dominant legs. The Pearson product-moment coefficient of correlation was used to analyse the correlations between the bilateral and unilateral vertical jump variables and the physical tests. The bilateral vertical jump performance (in both SJ and CMJ) was closely related to sprinting and JS power performances (r values ranging from 0.50 to 0.73; P< 0.05). In contrast, no significant associations were found between jump asymmetries and performance measures. Our data suggest that asymmetry scores derived from unilateral vertical jumps are not capable of influencing the speed-power performance of professional female soccer players.

#7 Adolescent female soccer players' soccer-specific warm-up effects on performance and inter-limb asymmetries
Reference: Biol Sport. 2019 Sep;36(3):199-207. doi: 10.5114/biolsport.2019.85453. Epub 2019 May 28.
Authors: Pardos-Mainer E, Casajús JA, Gonzalo-Skok O
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Summary: No studies have assessed whether changes in physical performance and inter-limb asymmetries (ILA) can be achieved with the FIFA 11+ prevention programme in adolescent female soccer players. The aim of this study was to assess the effect of the FIFA 11+ programme compared with a standard warm-up on physical performance and ILA in adolescent female soccer players. Thirty-six adolescent female soccer players were randomly assigned to an experimental (EG; n = 19) or a control group (CG; n = 17). Unilateral/bilateral countermovement jump (CMJ), drop jump (DJ) and horizontal jump tests, two different change of direction tests, an ankle dorsiflexion test, the Y-Balance test (YBT) and inter-limb asymmetries were measured before and after 10 weeks of training. The results revealed no significant group-by-time interactions in the vast majority of variables (p>0.05). Paired t-test revealed significant improvements of the right [effect size (ES):0.56] and left (ES:0.49) CMJ, right (ES:0.74) and left (ES:0.54) DJ (ES:0.74), right (ES:1.27) and left (ES:1.26) posteromedial direction and right (ES:0.89) and left (ES:0.84) posterolateral direction in the YBT in the EG (p < 0.05). Right anterior direction in the YBT and V-cut test were significantly improved in both groups (p<0.05). For inter-limb asymmetry variables, no significant group-by-time interactions (ES:0 to 0.93) and an improvement between pre- and post-tests (ES:-0.76 to 0.49) were observed. Therefore, the FIFA 11+ programme led to improved unilateral jumping, dynamic balance and reduced lower extremity symmetries of several tests in adolescent female soccer players.

#8 Retraction Note: Assessing cardiorespiratory fitness of soccer players: is test specificity the issue?-a review
Reference: Sports Med Open. 2019 Oct 17;5(1):42. doi: 10.1186/s40798-019-0217-9.
Authors: Jemni M, Prince MS, Baker JS
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#9 Effect of Kinesio Taping and balance exercises on postural control in amateur soccer players: A randomised control trial
Reference: J Sports Sci. 2019 Dec;37(24):2853-2862. doi: 10.1080/02640414.2019.1677016. Epub 2019 Oct 15.
Authors: Inglés M, Serra-Añó P, Méndez ÀG, Zarzoso M, Aguilar-Rodríguez M, Suso-Martí L, Cuenca-Martínez F, Espí-López GV
Summary: The objective of this study was to determine the effect of Kinesio Taping (KT), alone or together with balance exercises (BE), on parameters related to postural control, such as dynamic balance, static balance and flexibility. Forty-four male amateur soccer players (mean age 24.45 (4.79) years) were randomly allocated to 3 groups: KT+BE that received KT and BE (n = 16); KTp+BE, in which the KT was used as a placebo (n = 15) and KT alone (n = 13). The intervention period lasted 4 weeks. Star Excursion Balance Test (SEBT), Unipedal Stance Test (UST) and the Toe Touch Test (TTT) were assessed at baseline (pre), two weeks after beginning the treatment (mid) and after the intervention (post). We observed a significant improvement on the SEBT (mid and post-treatment) and the UST (post-treatment), but not on the TTT in either KT+BE or KTp+BE groups post treatment. No differences were found either in KT group at any time point or between groups in any variable studied. In conclusion, KT functional correction technique does not improve static and dynamic balance when applied alone, whereas BE alone or combined with KT significantly improves these variables. None of these techniques has any effect on flexibility.

#10 Pediatric retinal damage due to soccer-ball-related injury: Results from the last decade
Reference: Eur J Ophthalmol. 2019 Oct 15:1120672119882332. doi: 10.1177/1120672119882332. [Epub ahead of print]
Authors: Leshno A, Alhalel A, Fogel-Levin M, Zloto O, Moisseiev J, Vidne-Hay O
Summary: The aim was to outline the incidence of posterior segment injuries related to soccer-ball blunt trauma in children. Retrospective search of the computerized hospital medical database between the years 2007 and 2017. All pediatric trauma cases were reviewed and cases with blunt trauma related to direct orbital/ocular hit from a soccer-ball were included. Cases were divided into two groups (non-severe and severe) based on the presence of sight-threatening findings on presentation (e.g. retinal tear, vitreous hemorrhage, retinal detachment, and macular edema). Out of 343 pediatric patients with relevant diagnoses, 14 (4.1%) were treated for injuries related to soccer-ball trauma. All patients were males at their early-to-mid teens (14.3 ± 2.1 years). The most common funduscopic finding was peripheral commotio retina (13, 93%). There was equal distribution between the two groups (seven each). Retinal injury in the severe group included retinal tear (3), vitreous hemorrhage (4), retinal detachment (1), and macular hole (1). Five patients in this group presented with visual acuity of 20/25 or better. Rate of external signs of injury were similar in both groups. Soccer-ball blunt trauma in children can cause significant posterior segment injuries regardless of the presence of external injury or ocular complaints. A thorough ocular exam is mandatory in all cases for the detection of vision-threatening retinal injuries.

#11 Acute sleep hygiene strategy improves objective sleep latency following a late-evening soccer-specific training session: A randomized controlled trial
Reference: J Sports Sci. 2019 Dec;37(23):2711-2719. doi: 10.1080/02640414.2019.1661938. Epub 2019 Sep 6.
Authors: Vitale JA, La Torre A, Banfi G, Bonato M
Summary: The aim of this study was to evaluate the effects of sleep hygiene (SH) education on sleep quality in soccer players after a late-evening small-sided-game (SSG) training session. Twenty-nine non-professional players were recruited and allocated to either an experimental group (EG, n = 17) that received SH education, or a control group (CG, n = 12). SSG consisted of 3 × 4 min in a 4vs4, with 3 min of recovery and was performed at 8.00 p.m. Sleep quality was monitored via actigraphy and sleep diary entries before (PRE) and two nights after (POST1, POST2) the SSG. Sleep latency (SL) differed between the two groups at POST1 (4.9 ± 5.4 vs. 15.5 ± 16.1 for EG and CG, respectively; p = 0.017, effect size [ES] = 2.0); SL values were lower at POST1 compared to PRE for the EG (-47%; p = 0.021, ES = 0.6). Subjective sleep quality was better in the EG than the CG at POST1 (8.6 ± 1.0 vs. 7.1 ± 2.0 for EG and CG, respectively; p = 0.016, ES = 0.9) with a significant improvement over PRE-values (+11.0%, p = 0.004, ES = 0.8). Although SL and subjective sleep quality did not decrease significantly from POST1 to POST2 values at POST2 no longer differed significantly form baseline and, hence, indicate that observed effects may be short-lasting. No other objective sleep indices were influenced by late-evening training or SH practices implemented by the EG. Soccer players may benefit from acute SH strategies to reduce the time to sleep onset after late-evening training sessions.





Latest research in football - week 41 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Isometric Posterior Chain Peak Force Recovery Response Following Match-Play in Elite Youth Soccer Players: Associations with Relative Posterior Chain Strength
Reference: Sports (Basel). 2019 Oct 1;7(10). pii: E218. doi: 10.3390/sports7100218.
Authors: Constantine E, Taberner M, Richter C, Willett M, Cohen DD
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Summary: The purpose of this study was to determine changes in two tests of lower limb isometric posterior chain force (IPC-F) following 90 min of match-play in elite youth soccer players and the interaction between relative strength and recovery profile. 14 players (age: 16 ± 2 years) performed 3 × 3 second IPC-F tests unilaterally at 30° and 90° of knee and hip flexion pre- and post-match, +24 h, +48 h, and +72 h post-match. Peak force was recorded for both limbs, combined and expressed relative to bodyweight (N/kg). A two-way repeated measures analysis of variance was performed to determine differences in force output between joint angles, time intervals and subjects. As there was no interaction between angle and time (p = 0.260), we report the change between timepoints as mean Δ in 90° + 30° IPC-F. Relative to pre-match IPC-F, there were significant decreases post (Δ = -18%; p > 0.001) and at +24 h (Δ = -8%; p = 0.040), no significant difference at +48 h (Δ = 0%; p = 0.992) and a significant increase at +72 h (Δ = +12%; p = 0.005). There was a large inter-individual variability in recovery profile at both angles and substantial differences between post-match deficits at 90° (-10.8%) compared to 30° (-20.7%). Higher pre-match IPC-F was correlated with the magnitude of IPC-F deficits at both angles and all time points (r = 0.56 to 0.70, p = < 0.01) except for post-match 90°. Regular IPC-F monitoring to determine the magnitude of match-induced fatigue and track recovery may help inform decision-making regarding modifications to individual players training load, particularly as there is a large inter-individual variability in response to competition. Further research is warranted to better understand and address the finding that stronger players showed larger force deficits and slower recovery following match-play.

#2 Investigating the Clinical Effect of Kinesio Tape on Muscle Performance in Healthy Young Soccer Players - A Prospective Cohort Study
Reference: Clinics (Sao Paulo). 2019 Sep 26;74:e1158. doi: 10.6061/clinics/2019/e1158. eCollection 2019.
Authors: Alrawaili SM
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Summary: Kinesio tape (KT) is a visible adhesive restorative tape that has typically been utilized for injury prevention, recovery, and even performance improvement, but limited studies have assessed the effect of KT on muscle performance. The purpose of this study was to investigate the clinical impact of KT on muscle performance in healthy young soccer players. Between 25 March and 21 April 2017, sixteen healthy soccer players with a mean age of 20±2.17 were enrolled in this prospective cohort study. All participants were selected from the college football team of Prince Sattam Bin Abdulaziz University. The muscle performance of the players was evaluated with an isokinetic dynamometer for the following three conditions: without tape, immediately after applying KT, and 8 hrs post-KT application while the tape remained on the same site. The differences in peak torque and total work among the three conditions were nonsignificant (p>0.05). Additionally, applying KT to the thigh muscles did not decrease or increase the performance of non injured healthy soccer players (p>0.05). KT does not lead to beneficial outcomes of muscle performance in healthy young soccer players.

#3 Biomechanical mechanisms of jumping performance in youth elite female soccer players
Reference: J Sports Sci. 2019 Oct 1:1-7. doi: 10.1080/02640414.2019.1674526. [Epub ahead of print]
Authors: Jeras NMJ, Bovend'Eerdt TJH, McCrum C
Summary: We aimed to determine key biomechanical parameters explaining age-related jumping performance differences in youth elite female soccer players. Multiple biomechanical parameters from countermovement (CMJ) squat (SJ) and drop (DJ) jump testing of elite female soccer players (n = 60) within the same national training centre were analysed across ages 9-11y, 12-14y and 15-19y. Effects of age group and jump type on jump height were found, with the older jumping higher than the younger groups in all jumps (P < 0.05). For DJ, higher reactive strength index was found for older, compared to each younger group (P < 0.001). For CMJ and SJ, peak power was the most decisive characteristic, with significant differences between each group for absolute peak power (P < 0.0001) and body-weight-normalised peak power in CMJ (57 ± 7W/kg, 50 ± 7W/kg, 44.7 ± 5.5W/kg; P < 0.05) and between the older and each younger group in SJ (56.7 ± 7.1W/kg, 48.9 ± 7.1W/kg, 44.6 ± 6W/kg; P < 0.01). Age-related differences in jumping performance in youth elite female soccer players appear to be due to power production during standing jumps and by the ability to jump with shorter ground contact times during reactive jumps.

#4 Effect of Match Location, Team Ranking, Match Status and Tactical Dimensions on the Offensive Performance in Spanish 'La Liga' Soccer Matches
Reference: Front Psychol. 2019 Sep 12;10:2089. doi: 10.3389/fpsyg.2019.02089. eCollection 2019.
Authors: González-Rodenas J, Aranda-Malavés R, Tudela-Desantes A, Calabuig Moreno F, Casal CA, Aranda R

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Summary: The aim of this paper was to study the combined effects of tactical and contextual dimensions on achieving offensive performance in open play possessions from Spanish "La Liga" soccer matches. 1860 team possessions from 20 random matches were evaluated by means of multidimensional observation. Multilevel regression models were constructed to predict the probability to achieve offensive performance according to the tactical and contextual dimensions registered in each possession. Performing penetrative actions after recovering the ball (OR = 1.497; 95% CI: 1.022-2.192; P < 0.05), and progressing by fast attacks (OR = 3.588; 95% CI: 2.045-6.294; p < 0.001) or counterattacks (OR = 7.097; 95% CI: 3.530-14.269; P < 0.001) was more effective to create scoring opportunities than performing a non-penetrative action and progressing by combinative attack, respectively. Also, progressing by long possessions (OR = 5.057; 95% CI: 2.406-10.627; p < 0.001) was more effective than progressing by short possessions to create scoring opportunities. As for contextual dimensions, multivariate analyses showed how playing at home and against high-ranked opponents registered more likelihood of achieving offensive penetration, although no associations were found in the production of scoring opportunities. Tactical dimensions as initial penetration, type of attack and possession length played an important role on achieving offensive penetration and goal scoring opportunities in Spanish Soccer "La Liga".

#5 Transformational Leadership, Task-Involving Climate, and Their Implications in Male Junior Soccer Players: A Multilevel Approach
Reference: Int J Environ Res Public Health. 2019 Sep 28;16(19). pii: E3649. doi: 10.3390/ijerph16193649.
Authors: Álvarez O, Castillo I, Molina-García V, Tomás I
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Summary: Despite the well-known positive consequences of transformational coaches in sport, there is still little research exploring the mechanisms through which coaches' transformational leadership exerts its impact on athletes. Multilevel SEM was used to examine the relationship between coaches' transformational leadership style, a task-involving climate, and leadership effectiveness outcome criteria (i.e., players' extra effort, coach effectiveness, and satisfaction with their coach), separately estimating between and within effects. A representative sample of 625 Spanish male soccer players ranging from 16 to 18 years old and nested in 50 teams completed a questionnaire package tapping the variables of interest. Results confirmed that at the team level, team perceptions of transformational leadership positively predicted teams' perceptions of task climate, which in turn positively predicted the three outcome criteria. At the individual level, players' perceptions of transformational leadership positively predicted teams' perceptions of task climate, which in turn positively predicted teams' extra effort and coach effectiveness. Mediation effects appeared at the team level for all the outcome criteria, and at the individual only for extra effort. Transformational leadership is recommended to enhance task climate, in order to increase players' extra effort, their perceptions of the effectiveness of their coach, and their satisfaction with his/her leadership style.

#6 Inspiratory muscle training improves performance of a repeated sprints ability test in professional soccer players
Reference: J Bodyw Mov Ther. 2019 Jul;23(3):452-455. doi: 10.1016/j.jbmt.2019.01.016. Epub 2019 Jan 30.
Authors: Cavalcante Silva RL, Hall E, Maior AS
Summary: The aim of this study was to investigate the effects of IMT on exercise tolerance, repeated sprint ability (RSA) performance, maximal inspiratory pressure (MIP), and peak inspiratory flow (PIF) in a cohort of professional male soccer players. Twenty-two healthy male professional soccer players (18.3 ± 1.4 years; 174.5 ± 6.1 cm; 70.5 kg ± 4.6 kg; body fat 10.1 ± 4.2%) from a club in the Brazilian first division soccer league participated in this study. IMT consisted of 15 and 30 self-paced inspiratory breaths (each to 50% maximal static inspiratory pressure [P0]) in the 1-and 2-week intervention period, respectively. IMT was performed prior to soccer training (1 sets.d-1; 6 d.wk-1) with repeated sprint ability (RSA) assessed pre- and post- the 2-week period of IMT. Statistical analyses identified a significant (p < 0.001) decrease in sprint time post-IMT. Additionally, RSAbest, RSAmean, total sprint time and percentage of RSA performance decrement (RSA % dec) also showed significant decreases (p < 0.0001) post-IMT. Additional measures including MIP and PIF were also significantly elevated (p < 0.0002) following the 2-week period of IMT. In conclusion, our results raise two important issues. Firstly, IMT demonstrated enhanced inspiratory muscle strength in professional soccer players. Secondly, this increase in inspiratory muscle efficiency led to a decrease in sprint time and improved exercise tolerance. We recommend that a standard training protocol be developed and tested in an experimental and control group with a large representative sample.

#7 Regarding: "Inspiratory muscle training improves performance of a repeated sprints ability test in professional soccer players"
Reference: J Bodyw Mov Ther. 2019 Jul;23(3):443-444. doi: 10.1016/j.jbmt.2019.03.012. Epub 2019 Apr 2.
Authors: Matte DL, Ribeiro GS, Esquivel MS, Karsten M
Summary: The Journal of Bodywork & Movement Therapies recently published an article by Silva et al., entitled "Inspiratory muscle training improves performance of a repeated sprints ability test in professional soccer players" (Silva et al., 2019). After close reading we find that the new findings of Silva et al., (2019) are relevant and provide a promising indication that IMT can improve the performance of young male soccer players. However, some additional important points must be considered when interpreting these positive findings.

#8 Session-To-Session Variations of External Load Measures of Youth Soccer Players in Medium-Sided Games
Reference: Int J Environ Res Public Health. 2019 Sep 26;16(19). pii: E3612. doi: 10.3390/ijerph16193612.
Authors: Clemente FM, Rabbani A, Kargarfard M, Nikolaidis PT, Rosemann T, Knechtle B
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Summary: The aim of this study was to analyze the variability of time-motion variables during five vs. five games when completed within the same session as, and between, two different sessions. Ten under-19 male soccer players (18.27 ± 0.47 years old) participated in this study. The five vs. five matches (3 × 5 min) were played twice with a 3-day interval of rest in the same week. Moderate between-session variations were observed for TD (total distance) (range coefficient of variation (CV), 6.9; 8.3%, confidence interval (CI), (5.0; 14.0), standardized typical error (STE), 0.68; 1.06, (0.64; 1.75)) and RD (running distance) (range CV, 53.3; 145.7%, (36.6; 338.9), STE, 0.83; 1.09, (0.60; 1.76)). PL (player load) showed small variations (range CV, 4.9; 6.0%, [3.6; 10.1], STE, 0.37; 0.43, (0.27; 0.71)). In within-session analyses for examining the differences between sets, a small decrease was observed in RD in set 3 versus set 2 (-14.8%, 90% CI (-32.1; 6.9%); standardized difference (ES): -0.39 (0.95; 0.16)). TD decreased with moderate (-3.5%, (-6.8; -0.1%); ES: -0.65(-1.30; -0.01)) and large (-8.2%, (-11.4; -4.9%); ES: -1.58(-2.24; -0.92)) effects in sets 2 and 3, respectively, versus set 1. Our results suggest that PL is the most stable performance variable. It was also verified that measures had a progressive decreasing tendency within a session.

#9 Head impact exposure in youth football - are current interventions hitting the target?
Reference: Scand J Med Sci Sports. 2019 Oct 4. doi: 10.1111/sms.13562. [Epub ahead of print]
Authors: Sandmo SB, Andersen TE, Koerte IK, Bahr R
Summary: Restrictions on heading in youth football have been implemented in some countries to limit head-impact exposure. However, current interventions remain poorly guided by evidence. Our objective was to quantify heading exposure in youth football, assessing the effects of sex and age. Football matches played during an international youth football tournament with no heading restrictions were directly observed, including players from both sexes (11-19 years). The elite senior level was included for comparison, using video analysis. All heading events were registered, classified and assigned to individual players. Heading rates were calculated for each sex and age group. We observed a total of 267 matches, corresponding to 4011 player hours (1927 player hours for females, 2083 player hours for males). Males headed more frequently than females (2.7 vs. 1.8 headers/player hour; p<0.001). Heading rates increased with age (ANOVA, p<0.001), approaching the elite senior level for players 16 years and older. There was substantial variation within teams for all age and sex groups, with the widest range (1-18 headers) observed for girls aged 19. Girls younger than 12 years had the lowest exposure, with an average of less than two players per team heading the ball, each with 1-2 headers. In conclusion, age and sex influence head-impact exposure in youth football, and warrants careful consideration when introducing injury prevention measures. Males are more frequently exposed than females, heading rates increase with age, and there is substantial variation between players. Heading is a rare event in the youngest age groups, especially among females.

#10 Trapezoid Fracture Associated with Scaphoid Fracture in a Football Goalkeeper
Reference: Case Rep Orthop. 2019 Sep 5;2019:7949754. doi: 10.1155/2019/7949754. eCollection 2019.
Authors: Yamamoto T, Matsushita T, Ito K, Matsushima S, Yoshida K, Kuroda R
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Summary: A 19-year-old male who played as a football goalkeeper visited our hospital with complaints of sustained pain from the right wrist to the hand after punching a ball. Scaphoid fracture was diagnosed on plain radiographs, whereas trapezoid fracture was overlooked. Computed tomography revealed a displaced trapezoid fracture associated with a scaphoid fracture. Both fractures were successfully treated by open reduction and internal fixation using cannulated screws. Almost complete bone union was achieved at 5 months after surgery. The patient returned to play as a football goalkeeper. The simultaneous occurrence of trapezoid and scaphoid fractures has never been reported. Trapezoid fractures are rare and can be overlooked on plain radiographs, as what happened in the present case, because the trapezoid is small and overlaps with other carpal bones on plain radiographs. If there is sustained pain in the wrist and hand after punching, combined trapezoid and scaphoid fractures should be considered as the possible injury.

#11 Is Physical Performance a Differentiating Element between More or Less Successful Football Teams?
Reference: Sports (Basel). 2019 Sep 30;7(10). pii: E216. doi: 10.3390/sports7100216.
Authors: Asian Clemente JA, Requena B, Jukic I, Nayler J, Hernández AS, Carling C
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Summary: This study investigated the time-motion characteristics of football teams in the Spanish first division, in relation to their final competitive level as defined by league position (Champions League, Europa League, Upper mid-table, lower mid-table and relegation). Match observations (n = 9641) were collected using a multiple-camera computerized tracking system during the 2013-2014 competitive season. The following match parameters were analyzed: total distance, relative distance (m·min-1), distance < 14 km·h-1, >14 km·h-1, between 14-21 km·h-1, >21 km·h-1, and >24 km·h-1. Total distance and distance at different velocities (>14, 21, and 24 km·h-1) in and out of ball possession were also analyzed. A repeated analysis of variance and a comparison of effect sizes were carried out to compare the performance of the teams. The analysis of the data showed differences in physical performance characteristics between competitive levels. The volume of distance covered in the variables analyzed did not relate to success in soccer. Both successful and unsuccessful teams presented the same running requirements at higher velocities. These findings provide valuable information about the physical demands of the running requirements according to their final position in the league table.

#12 Community-based football in men with prostate cancer: 1-year follow-up on a pragmatic, multicentre randomised controlled trial
Reference: PLoS Med. 2019 Oct 1;16(10):e1002936. doi: 10.1371/journal.pmed.1002936. eCollection 2019 Oct.
Authors: Bjerre ED, Petersen TH, Jørgensen AB, Johansen C, Krustrup P, Langdahl B, Poulsen MH, Madsen SS, Østergren PB, Borre M, Rørth M, Brasso K, Midtgaard J
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Summary: Physical exercise has been shown to be effective in relation to fatigue, aerobic fitness, and lower body strength in men with prostate cancer. However, research into the clinically relevant effects of interventions conducted in heterogeneous patient populations and in real-life clinical practice settings is warranted. We conducted a pragmatic, multicentre, parallel randomised controlled trial in 5 Danish urological departments. Recruitment began in May 2015, the first participant was randomised in June 2015, and the last participant was included in February 2017. In total, 214 men with prostate cancer were randomly assigned to either 6 months of free-of-charge football training twice weekly at a local club (football group [FG]) (n = 109) or usual care (usual care group [UG]) (n = 105), including brief information on physical activity recommendations at randomisation. Participants were on average 68.4 (SD 6.2) years old, 157 (73%) were retired, 87 (41%) were on castration-based treatment, 19 (9%) had received chemotherapy, and 41 (19%) had skeletal metastases at baseline. In this 1-year follow-up study, we evaluated the effects of community-based football training on the following outcomes: primary outcome, quality of life; secondary outcomes: continuation of football after 6 months, hip and lumbar spine bone mineral density (BMD), mental health score, fat and lean body mass, and safety outcomes, i.e., fractures, falls, and hospital admissions. Intention to treat (ITT) and per protocol (PP) analyses were conducted. No statistically significant between-group difference was observed in change in prostate-cancer-specific quality of life (ITT: 1.9 points [95% CI -1.9 to 5.8], p = 0.325; PP: 3.6 points [95% CI -0.9 to 8.2], p = 0.119). A statistically significant between-group difference was observed in change in total hip BMD, in favour of FG (0.007 g/cm2 [95% CI 0.004 to 0.013], p = 0.037). No differences were observed in change in lumbar spine BMD or lean body mass. Among patients allocated to football, 59% chose to continue playing football after the end of the 6-month intervention period. At 1-year follow-up in the PP population, FG participants had more improvement on the Mental Component Summary (2.9 [95% CI 0.0 to 5.7], p = 0.048 points higher) than UG participants, as well as a greater loss of fat mass (-0.9 kg [95% CI -1.7 to -0.1], p = 0.029). There were no differences between groups in relation to fractures or falls. Hospital admissions were more frequent in UG compared to FG (33 versus 20; the odds ratio based on PP analysis was 0.34 for FG compared to UG). There were 3 deaths in FG and 4 in UG. Main limitations of the study were the physically active control group and assessment of physical activity by means of self-report. In this trial, participants allocated to football appeared to have improved hip BMD and fewer hospital admissions. Men who played football more than once a week for 1 year lost fat mass and reported improved mental health. Community-based football proved to be acceptable, even when club membership was not subsidised.





Latest research in football - week 40 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Is Playing Soccer More Osteogenic for Females Before the Pubertal Spurt?
Reference: J Hum Kinet. 2019 Jul 5;67:153-161. doi: 10.2478/hukin-2018-0074. eCollection 2019 Jun.
Authors: Lozano-Berges G, Matute-Llorente Á, Gómez-Bruton A, González-Agüero A, Vicente-Rodríguez G, Casajús JA
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Summary: The aims of this study were to assess bone mass in children and adolescent soccer players and to evaluate the influence of both gender and pubertal status on bone mass. A total of 110 soccer players (75 males / 35 females; 12.73 ± 0.65 / 12.76 ± 0.59 years) participated in this cross-sectional study. They were divided into two groups according to their pubertal status. Bone and lean masses were measured with Dual-energy X-ray Absorptiometry. An independent t-test and an adjusted by subtotal lean and training experience multivariate analysis of covariance were used to analyse the differences in bone mass values between genders and maturity status. Female soccer players presented higher bone mass values than their male counterparts in most of the measured weight-bearing sites. Moreover, when stratifying by pubertal status, peripubertal and postpubertal females had higher subtotal body and lumbar spine bone mass than males. Comparing between pubertal status groups before adjustment, both male and female postpubertal players showed higher bone mass than their pubertal counterparts. After adjusting, these differences disappeared and, in fact results were inverted as bone mass at the femoral neck was higher in both male and female peripubertal soccer players than in postpubertal players. Bone mass seems to be more intensely stimulated by playing soccer in female than male players, particularly in the lumbar spine. The results of peripubertal players showing higher bone mass at the femoral neck after adjusting suggest that playing soccer during the peripubertal stage could

#2 Decrease in Attentional Performance After Repeated Bouts of High Intensity Exercise in Association-Football Referees and Assistant Referees
Reference: Front Psychol. 2019 Sep 6;10:2014. doi: 10.3389/fpsyg.2019.02014. eCollection 2019.
Authors: Schmidt SL, Schmidt GJ, Padilla CS, Simões EN, Tolentino JC, Barroso PR, Narciso JH, Godoy ES, Costa Filho RL
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Summary: Referees and assistant referees are submitted to high physical stress during matches. Pressure to make decisions in front of large crowds is another potential stressor. These two stressors can impair attention executive control, depending on physical fitness and individual vulnerability or resilience to situational pressure. Error percentage for referees and assistants may reach around 14% during a soccer match. Although previous studies have suggested that soccer referees and assistants should take cognitive assessments, they are only required by Fédération Internationale de Football Association (FIFA) to demonstrate knowledge of the rules and pass annually in a fitness test (FIFA-Test). This study aimed to assess attention performance in referees and assistants before and after the mandatory FIFA-Test. It is hypothesized that the high physical demands associated with the pressure to pass the FIFA-Test would interfere with attention performance. The sample included 33 referees and 20 assistants. The Continuous Visual Attention Test (CVAT) consisted of a 15-min Go/No-go task. Performance in the CVAT is based on four variables: omission and commission errors, reaction time, and variability of reaction time (VRT). Failure in the CVAT was defined by a performance below the 5th percentile of the age- and sex-matched normative data in at least one variable of the CVAT. Before the FIFA-Test all participants performed the CVAT. The second CVAT began 3-7 min directly following completion of the FIFA-test. Considering only the officials who passed both the FIFA-Test and the first CVAT (19 referees and 15 assistants), 44% (9 referees and 6 assistants) exhibited a performance decline in the second CVAT. A significant increase in VRT was found after the high intensity exercise. As increase in VRT is thought to reflect executive dysfunctions and lapses of attention, we concluded that physical fitness alone may not be enough to help officials cope with the physical and contextual stresses associated with the FIFA-Test. These data suggest that over 35% of soccer referees and their assistants who were considered physically able to referee matches may not be mentally prepared for the attentional demands of refereeing soccer matches.

#3 You Don't Bend It Like Beckham if You're Female and Reminded of It: Stereotype Threat Among Female Football Players
Reference: Front Psychol. 2019 Aug 28;10:1963. doi: 10.3389/fpsyg.2019.01963. eCollection 2019.
Authors: Grabow H, Kühl M
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Summary: Originally, the stereotype threat effect - poorer performance due to a fear of fulfilling a negative stereotype about one's group - was demonstrated for cognitive tasks (e.g. Steele and Aronson, 1995, or Steele, 1997). Drawing on the widespread stereotype of women being unable to play football we experimentally tested (N = 80) whether a respective threat affected female football players' goal scoring precision, i.e. a complex and demanding motor task. Those participants who were reminded of the stereotype scored significantly less hits than those not reminded. Additionally, deviations from the instruction during task execution (e.g. shooting from another distance than demanded or using the wrong foot) were recorded. Stereotype threat did not affect this comparatively more cognitive task of following instructions correctly. In order to explore underlying mechanisms of the observed stereotype effect, several potential mediators, e.g. measures of cognitive interference, or collective identification, were tested. None emerged as an unquestionable link between threat and motor performance. We discuss, however, why collective identification - in comparison to cognitive demand - appears to be the more promising explanatory concept.

#4 Corrigendum: Football Players Do Not Show "Neural Efficiency" in Cortical Activity Related to Visuospatial Information Processing During Football Scenes: An EEG Mapping Study
Reference: Front Psychol. 2019 Aug 27;10:1877. doi: 10.3389/fpsyg.2019.01877. eCollection 2019.
Authors: Del Percio C, Franzetti M, De Matti AJ, Noce G, Lizio R, Lopez S, Soricelli A, Ferri R, Pascarelli MT, Rizzo M, Triggiani AI, Stocchi F, Limatola C, Babiloni C
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#5 Strategies for Maintaining the Coach-Analyst Relationship Within Professional Football Utilizing the COMPASS Model: The Performance Analyst's Perspective
Reference: Front Psychol. 2019 Sep 10;10:2064. doi: 10.3389/fpsyg.2019.02064. eCollection 2019.
Authors: Bateman M, Jones G
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Summary: There is a considerable body of research by that has investigated the coach-athlete relationship in sport. However, given the multi-disciplinary nature of modern elite coaching, there is a scarcity of research focusing on the relationship between coaches and other members of the coaching and support team. This study examined the perceptions of six elite professional football analyst's relationships with their respective coaches. Semi structured interviews utilizing the COMPASS Framework were conducted focusing on Conflict, Openness, Motivation, Preventative Strategies, Assurance, Support, and Social Networks. The results verified that the COMPASS Model of relationship maintenance was applicable to this dyad. Content analysis indicated that there was 215 raw data units comprising of 16 higher order themes across the model which was further broken down into 29 lower order themes. All aspects of the model were found to contribute toward a positively maintained relationship. Having an open relationship underpinned by honesty and being able to provide an opinion was seen as the highest rated attribute that was closely followed by supporting the coach by understanding their requirements for successful coaching practice. Not meeting the coach's expectations was found to cause conflict and was further highlighted by an inductive analysis that revealed the existence of a relationship that is fundamentally dictated by the coach. Implications of this investigation are that professionals which support elite performers need to set out clear expectations of working practice and hierarchies in order to minimize the chance of internal conflict that can impact on the service levels received by the performer.

#6 A study protocol for the development and internal validation of a multivariable prognostic model to determine lower extremity muscle injury risk in elite football (soccer) players, with further exploration of prognostic factors
Reference: Diagn Progn Res. 2019 Sep 19;3:19. doi: 10.1186/s41512-019-0063-8. eCollection 2019.
Authors: Hughes T, Riley R, Sergeant JC, Callaghan MJ
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Summary: Indirect muscle injuries (IMIs) are a considerable burden to elite football (soccer) teams, and prevention of these injuries offers many benefits. Preseason medical, musculoskeletal and performance screening (termed periodic health examination (PHE)) can be used to help determine players at risk of injuries such as IMIs, where identification of PHE-derived prognostic factors (PF) may inform IMI prevention strategies. Furthermore, using several PFs in combination within a multivariable prognostic model may allow individualised IMI risk estimation and specific targeting of prevention strategies, based upon an individual's PF profile. No such models have been developed in elite football and the current IMI prognostic factor evidence is limited. This study aims to (1) develop and internally validate a prognostic model for individualised IMI risk prediction within a season in elite footballers, using the extent of the prognostic evidence and clinical reasoning; and (2) explore potential PHE-derived PFs associated with IMI outcomes in elite footballers, using available PHE data from a professional team. This is a protocol for a retrospective cohort study. PHE and injury data were routinely collected over 5 seasons (1 July 2013 to 19 May 2018), from a population of elite male players aged 16-40 years old. Of 60 candidate PFs, 15 were excluded. Twelve variables (derived from 10 PFs) will be included in model development that were identified from a systematic review, missing data assessment, measurement reliability evaluation and clinical reasoning. A full multivariable logistic regression model will be fitted, to ensure adjustment before backward elimination. The performance and internal validation of the model will be assessed. The remaining 35 candidate PFs are eligible for further exploration, using univariable logistic regression to obtain unadjusted risk estimates. Exploratory PFs will also be incorporated into multivariable logistic regression models to determine risk estimates whilst adjusting for age, height and body weight. This study will offer insights into clinical usefulness of a model to predict IMI risk in elite football and highlight the practicalities of model development in this setting. Further exploration may identify other relevant PFs for future confirmatory studies and model updating, or influence future injury prevention research.

#7 Limited positive effects on jump-landing technique in girls but not in boys after 8 weeks of injury prevention exercise training in youth football
Reference: Knee Surg Sports Traumatol Arthrosc. 2019 Sep 20. doi: 10.1007/s00167-019-05721-x. [Epub ahead of print]
Authors: Lindblom H, Waldén M, Carlfjord S, Hägglund M
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Summary: The aim was to evaluate changes in jump-landing technique in football-playing boys and girls after 8 weeks of injury prevention training. Four boys' and four girls' teams (mean age 14.1 ± 0.8 years) were instructed to use either the original Knee Control injury prevention exercise programme (IPEP) or a further developed IPEP, Knee Control + , at every training session for 8 weeks. Baseline and follow-up testing of jump-landing technique included drop vertical jumps (DVJ), assessed subjectively and with two-dimensional movement analysis, and tuck jump assessment (TJA). Only minor differences in intervention effects were seen between the two IPEPs, and results are therefore presented for both intervention groups combined. At baseline 30% of the boys showed good knee control during the DVJ, normalised knee separation distances of 77-96% (versus hip) and a median of 3 flaws during the TJA. Among girls, 22% showed good knee control, normalised knee separation distances of 67-86% and a median of 4 flaws during the TJA. At follow-up, boys and girls performed significantly more jumps during TJA. No changes in jump-landing technique were seen in boys, whereas girls improved their knee flexion angle at initial contact in the DVJ (mean change + 4.7°, p < 0.001, 95% CI 2.36-6.99, d = 0.7) and their TJA total score (- 1 point, p = 0.045, r = - 0.4). The study showed small positive effects on jump-landing technique in girls, but not in boys, after 8 weeks of injury prevention training.

#8 Prevention of severe knee injuries in men's elite football by implementing specific training modules
Reference: Knee Surg Sports Traumatol Arthrosc. 2019 Sep 20. doi: 10.1007/s00167-019-05706-w. [Epub ahead of print]
Authors: Krutsch W, Lehmann J, Jansen P, Angele P, Fellner B, Achenbach L, Krutsch V, Nerlich M, Alt V, Loose O
Summary: Injury prevention of knee injuries by means of training and warm-up exercises has been investigated in several studies in amateur football. However, the number of investigations in elite football is limited despite the currently higher injury incidence of severe knee injuries. Therefore, the purpose of this study was to investigate whether specifically adapted preventive training modules may reduce severe knee injuries in elite football. In a prospective controlled cohort study of elite football players in Germany, an injury prevention programme with 5 modules was implemented in the season of 2015-2016. The training modules were specifically adapted to this skill level and based on scientific evidence, team coach preferences, and the specific environment of this playing level. Of the 62 teams taking part in this study, 26 used the new trainings modules and 36 continued their standard programme as a control group. Success of the programme was documented by means of an injury report over one season. The primary outcome was reduction in severe knee injuries. A pre-seasonal investigation had identified five modules to be implemented in the training routine. Postural stability, mobilisation of lower extremity joints, leg and trunk stabilisation, jumping, and landing exercises as well as agility movements were incorporated into the programme to prevent severe knee injuries in elite football. Over the season, the study group (529 players) with the adapted training modules had sustained 52 severe knee injuries (incidence: 0.38 per 1000 h football exposure; prevalence: 9.8%) compared to 108 severe knee injuries in the control group (601 players) using the standard programme (incidence: 0.68 per 1000 h football exposure; prevalence: 18.0%; p < 0.05). The overall injury incidence for any other type of injury was comparable between the two groups (3.3 vs. 3.4 in h 1000 football, n.s.). Appropriate preventive training modules reduce severe knee injuries in elite football significantly. The key for the sustainability of preventive training measures are programmes specifically adapted to the demands of the playing level and to the preferences of the coaches

#9 Professional football clubs' involvement in health promotion in Spain: an audit of current practices
Reference: Health Promot Int. 2019 Sep 20. pii: daz097. doi: 10.1093/heapro/daz097. [Epub ahead of print]
Authors: Lozano-Sufrategui L, Pringle A, Zwolinsky S, Drew KJ
Summary: The implementation of effective community-based health interventions within Spanish football clubs has the potential to positively influence the public health agenda and enable the healthcare system in Spain to be more successful and sustainable. This paper aims to explore the involvement of Spanish football clubs in health promotion activities, their potential for future involvement and what that would require. A mixed methods explanatory sequential design, with a purposive sample of La Liga clubs. Data collection included online questionnaires and phone interviews. Quantitative methods enabled us to describe the number and types of programmes the clubs are currently involved in. Qualitative data was useful to further unpick the processes followed by the clubs in planning and developing health promotion programmes, while identifying any determinants to change. Seventeen clubs completed questionnaires and 11 participated in interviews. Clubs generally support inclusive programmes that target disadvantaged groups. Health-related programmes focus on healthy eating, physical activity and blood donation. Thematic analysis of interviews with 11 representatives of La Liga clubs resulted in three-key themes. These related to: (i) Diversity of programmes; (ii) (Lack of) evidence-based approaches to intervention design and evaluation and (iii) Contrasting views about a club's role in health promotion interventions. Spanish football clubs have potential to reach into communities that are currently underserved. However, there is limited infrastructure and understanding within the clubs to do this. Nevertheless, there is huge opportunity for organizations with public health responsibility in Spain to implement translational approaches within football-based settings.

#10 Defining a historic football team: Using Network Science to analyze Guardiola's F.C. Barcelona
Reference:  Sci Rep. 2019 Sep 19;9(1):13602. doi: 10.1038/s41598-019-49969-2.
Authors: Buldú JM, Busquets J, Echegoyen I, Seirul Lo F
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Summary: The application of Network Science to social systems has introduced new methodologies to analyze classical problems such as the emergence of epidemics, the arousal of cooperation between individuals or the propagation of information along social networks. More recently, the organization of football teams and their performance have been unveiled using metrics coming from Network Science, where a team is considered as a complex network whose nodes (i.e., players) interact with the aim of overcoming the opponent network. Here, we combine the use of different network metrics to extract the particular signature of the F.C. Barcelona coached by Guardiola, which has been considered one of the best teams along football history. We have first compared the network organization of Guardiola's team with their opponents along one season of the Spanish national league, identifying those metrics with statistically significant differences and relating them with the Guardiola's game. Next, we have focused on the temporal nature of football passing networks and calculated the evolution of all network properties along a match, instead of considering their average. In this way, we are able to identify those network metrics that enhance the probability of scoring/receiving a goal, showing that not all teams behave in the same way and how the organization Guardiola's F.C. Barcelona is different from the rest, including its clustering coefficient, shortest-path length, largest eigenvalue of the adjacency matrix, algebraic connectivity and centrality distribution.

#11 Improved maximal strength is not associated with improvements in sprint time or jump height in high-level female football players: a clusterrendomized controlled trial
Reference: BMC Sports Sci Med Rehabil. 2019 Sep 17;11:20. doi: 10.1186/s13102-019-0133-9. eCollection 2019.
Authors: Pedersen S, Heitmann KA, Sagelv EH, Johansen D, Pettersen SA
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Summary: Maximal strength increments are reported to result in improvements in sprint speed and jump height in elite male football players. Although similar effects are expected in females, this is yet to be elucidated. The aim of this study was to examine the effect of maximal strength training on sprint speed and jump height in high-level female football players. Two female football teams were team-cluster-randomized to a training group (TG) performing maximal strength training (MST) twice a week for 5 weeks, or control group (CG) doing their regular pre-season preparations. The MST consisted of 3-4 sets of 4-6 repetitions at ≥85% of 1 repetitions maximum (1RM) in a squat exercise. Sprint speed and jump height were assessed in 5-, 10- and 15 m sprints and a counter-movement jump (CMJ) test, respectively. Nineteen participants in TG (18.3 ± 2.7 years) and 14 in CG (18.3 ± 2.4 years) completed pre- and posttests and were carried forward for final analyses. There was no improvement in neither of the sprint times (p > 0.36), nor jump height (p = 0.87). The players increased their 1RM in squats (main of effect of time: p < 0.00, pη2 = 0.704), and an interaction effect of time x group was observed (p < 0.00, pη2 = 0.516) where the TG increased their 1RM more than the CT (between subjects effects: p < 0.001, pη2 = 0.965). MST improved maximal strength in female football players to a large extent; however, the improvement in maximal strength did not result in any transference to sprint speed or jump height.

#12 Acute Surgical Excision of a Traumatic Fat Fracture in a Professional Soccer Player
Reference: J Orthop Case Rep. 2019;9(3):68-71. doi: 10.13107/jocr.2250-0685.1426.
Authors: Kayani B, Ayuob A, Onochie E, Haddad FS
Summary: Surgical excision of fat fractures is often reserved for patients with large chronic deformities to improve cosmetic appearance. To our knowledge, the acute surgical management of a traumatic fat fracture has not been previously reported. This case report describes the management of a professional soccer player that developed a traumatic fat fracture over the lateral thigh. The patient presented with persistent pain, reduced range of movement, and inability to participate in sporting activity. Symptoms were refractory to non-operative treatment. Following acute surgical excision of the fat fracture, the patient was able to make an early return to sporting activity with no complications at short-term follow-up. Acute surgical excision of a traumatic fat fracture may be used as an avenue for improving pain, enhancing functional rehabilitation, and facilitating early return to pre-injury level of function.

#13 The Influence of Caffeine Expectancies on Simulated Soccer Performance in Recreational Individuals
Reference: Nutrients. 2019 Sep 25;11(10). pii: E2289. doi: 10.3390/nu11102289.
Authors: Shabir A, Hooton A, Spencer G, Storey M, Ensor O, Sandford L, Tallis J, Higgins MF
Summary: Caffeine (CAF) has been reported to improve various facets associated with successful soccer play, including gross motor skill performance, endurance capacity and cognition. These benefits are primarily attributed to pharmacological mechanisms. However, evidence assessing CAF's overall effects on soccer performance are sparse with no studies accounting for CAF's potential psychological impact. Therefore, the aim of this study was to assess CAF's psychological vs. pharmacological influence on various facets of simulated soccer performance. Utilising a double-dissociation design, eight male recreational soccer players (age: 22 ± 5 years, body mass: 78 ± 16 kg, height: 178 ± 6 cm) consumed CAF (3 mg/kg/body mass) or placebo (PLA) capsules, 60 minutes prior to performing the Loughborough Intermittent Shuttle Test (LIST) interspersed with a collection of ratings of perceived exertion (RPE), blood glucose and lactate, heart rate and performing the Loughborough Soccer Passing Test (LSPT). Whole-body dynamic reaction time (DRT) was assessed pre- and post- LIST, and endurance capacity (TLIM) post, time-matched LIST. Statistical analysis was performed using IBM SPSS (v24) whilst subjective perceptions were explored using template analysis. Mean TLIM was greatest (p < 0.001) for synergism (given CAF/told CAF) (672 ± 132 s) vs. placebo (given PLA/told PLA) (533 ± 79 s). However, when isolated, TLIM was greater (p = 0.012) for CAF psychology (given PLA/told CAF) (623 ± 117 s) vs. pharmacology (given CAF/told PLA) (578 ± 99 s), potentially, via reduced RPE. Although DRT performance was greater (p = 0.024) post-ingestion (+5 hits) and post-exercise (+7 hits) for pharmacology vs. placebo, psychology and synergism appeared to improve LSPT performance vs. pharmacology. Interestingly, positive perceptions during psychology inhibited LSPT and DRT performance via potential CAF over-reliance, with the opposite occurring following negative perceptions. The benefits associated with CAF expectancies may better suit tasks that entail lesser cognitive-/skill-specific attributes but greater gross motor function and this is likely due to reduced RPE. In isolation, these effects appear greater vs. CAF pharmacology. However, an additive benefit may be observed after combining expectancy with CAF pharmacology (i.e. synergism).





Latest research in football - week 39 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Preseason Hip/Groin Strength and HAGOS Scores Are Associated With Subsequent Injury in Professional Male Soccer Players
Reference: J Orthop Sports Phys Ther. 2019 Sep 17:1-34. doi: 10.2519/jospt.2020.9022. [Epub ahead of print]
Authors: Bourne MN, Williams M, Jackson J, Williams KL, Timmins RG, Pizzari T
Summary: Hip and groin injuries are a significant cause of time lost from training and competition in elite soccer. Therefore the aim was to explore the association between pre-season assessments of 1) isometric hip adductor and abductor strength using a novel field-test; and 2) the Copenhagen Hip and Groin Outcome Score (HAGOS), and subsequent hip/groin injury in professional male soccer players. In total, 204 elite male soccer players from ten professional Hyundai A-League and English Championship League clubs had assessments of hip adductor and abductor strength and completed the HAGOS in the 2017-18 pre-season. In-season hip/groin injuries were reported by team medical staff. Data reduction was conducted using principal component analysis. The principal component for HAGOS and three principal components for strength and imbalance measures were entered with age and prior hip/groin injury into a multivariable logistic regression model to determine their association with prospectively occurring hip/groin injury. Twenty-four players suffered at least one hip/groin injury throughout the 2017-18 season. The principal component for between-limb abduction imbalance (peak strength in the preferred [kicking] limb - non-preferred limb) (OR = 0.58, 95% CI = 0.38 to 0.90, p = 0.011), the principal component for peak adduction and abduction strength (OR = 0.71, 95% CI = 0.50 to 1.00, p=0.045), and the principal component for HAGOS (OR = 0.77, 95% CI = 0.62 to 0.96, p = 0.022), were independently associated with a reduced risk of future hip/groin injury. Receiver operator curve analysis of the whole model revealed an area under the curve of 0.76, which indicates a fair combined sensitivity and specificity of the included variables but an inability to correctly identify all subsequently injured players. Hip abduction imbalance, favouring the preferred kicking limb, higher levels of hip adductor and abductor strength, and superior HAGOS values, were associated with a reduced likelihood of future hip/groin injury in professional soccer players.

#2 Intra-individual variability of sleep and nocturnal cardiac autonomic activity in elite female soccer players during an international tournament
Reference: PLoS One. 2019 Sep 17;14(9):e0218635. doi: 10.1371/journal.pone.0218635. eCollection 2019.
Authors: Costa J, Figueiredo P, Nakamura F, Rago V, Rebelo A, Brito J
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Summary: The aim was to describe individual sleeping patterns and nocturnal cardiac autonomic activity of National team female soccer players during an international tournament. Twenty elite female soccer players (aged 25.2±3.1 years) wore wrist actigraph units and heart rate (HR) monitors during night-sleep throughout 9 consecutive days (6 day-time training sessions [DT], 2 day-time matches [DM], and 1 evening-time match [EM]) of an international tournament. Training and match loads were monitored using the session-rating of perceived exertion (s-RPE) and wearable 18-Hz GPS (total distance covered [TD], training and match exposure time, and high-speed running [HSR]) to characterize training and match loads. Individually, s-RPE, TD, exposure time, and HSR during training sessions ranged from 20 to 680 arbitrary units (AU), 892 to 5176 m, 20 to 76 min, and 80 to 1140 m, respectively. During matches, s-RPE, TD, exposure time, and HSR ranged from 149 to 876 AU, 2236 to 11210 m, 20 to 98 min, and 629 to 3213 m, respectively. Individually, players slept less than recommended (<7 hours) on several days of the tournament, especially after EM (n = 8; TST ranging between 6:00-6:54 h). Total sleep time coefficient of variation (CV) ranged between 3.1 and 18.7%. However, all players presented good sleep quality (i.e., sleep efficiency ≥75%; individual range between: 75-98%) on each day of the tournament. Most of the players presented small fluctuations in nocturnal cardiac autonomic activity (individual nocturnal heart rate variability [HRV] ranged from 3.91-5.37 ms and HRV CV ranged from 2.8-9.0%), while two players presented higher HRV CV (11.5 and 11.7%; respectively). Overall, this study highlights the substantial individual variability in sleep and HRV measures, suggesting the adoption of an individual approach to monitor sleep, training and match loads and recovery, to better understand how players cope with highly demanding competitions.

#3 The neuromuscular, endocrine and mood responses to a single versus double training session day in soccer players
Reference: J Sci Med Sport. 2019 Sep 5. pii: S1440-2440(18)31114-9. doi: 10.1016/j.jsams.2019.08.291. [Epub ahead of print]
Authors: Sparkes W, Turner AN, Cook CJ, Weston M, Russell M, Johnston MJ, Kilduff LP
Summary: This study profiled the 24h neuromuscular, endocrine and mood responses to a single versus a double training day in soccer players. Twelve semi-professional soccer players performed small-sided-games (SSG's; 4 vs 4+goalkeepers; 6×7-min, 2-min inter-set recovery) with neuromuscular (peak-power output, PPO; jump height, JH), endocrine (salivary testosterone, cortisol), and mood measures collected before (pre) and after (0h, +24h). The following week, the same SSG protocol was performed with an additional lower body strength training session (back-squat, Romanian deadlift, barbell hip thrust; 4×4 repetitions, 4-min inter-set recovery; 85% 1 rep-max) added at 2h after the SSG's. Between-trial comparisons revealed possible to likely small impairments in PPO (2.5±2.2Wkg-1; 90% Confidence Limits: ±2.2Wkg-1), JH (-1.3; ±2.0cm) and mood (4.6; ±6.1AU) in response to the double versus single sessions at +24h. Likely to very likely small favourable responses occurred following the single session for testosterone (-15.2; ±6.1pgml-1), cortisol (0.072; ±0.034ugdl-1) and testosterone/cortisol ratio (-96.6; ±36.7AU) at +24h compared to the double session trial. These data highlight that performance of two training sessions within a day resulted in possible to very likely small impairments of neuromuscular performance, mood score and endocrine markers at +24h relative to a single training session day. A strategy of alternating high intensity explosive training days containing multiple sessions with days emphasising submaximal technical/tactical activities may be beneficial for those responsible for the design and delivery of soccer training programs.

#4 Pre-exercise hypohydration prevalence in soccer players: a quantitative systematic review
Reference: Eur J Sport Sci. 2019 Sep 17:1-18. doi: 10.1080/17461391.2019.1669716. [Epub ahead of print]
Authors: Chapelle L, Tassignon B, Rommers N, Mertens E, Mullie P, Clarys P
Summary: Pre-exercise hypohydration can impair soccer performance and has been extensively studied in different soccer populations. Therefore, the aim of this systematic review was to report hypohydration prevalence, measured by blood or urine samples, in different soccer populations based on sex (males and females), performance level (professional and recreational players) and context (training sessions and games). The Pubmed, Web of Science and SPORTDiscus databases were systematically searched until November 2018. Data were pooled to compare hypohydration prevalence between the different subgroups. Following the systematic search selection process, 24 studies were included. The results indicated that overall pre-exercise hypohydration prevalence was 63.3 %, 37.4 % and 58.8 % for urine specific gravity (USG), urine osmolality (U Osm) and urine colour, respectively. Furthermore, no study implemented blood samples to examine hypohydration prevalence in soccer players. The subgroup analyses using USG data indicated that pre-exercise hypohydration prevalence was significantly higher amongst males (66.0 %; p = 0.001), professional soccer players (66.2 %; p = 0.020) and before a training session (79.6 %; p < 0.001). Pre-exercise hypohydration prevalence was 46.8 % among female soccer players, 55.6 % in recreational soccer players and 41,3 % before a game. The subgroup analyses using U Osm data indicated that hypohydration prevalence was significantly higher before a training session (52.6 %; p = 0.023). Based on these results, it can be concluded that hypohydration prevalence in soccer players is of major concern. Future research should explore how pre-exercise hydration status can be improved in a sustainable way.

#5 Analysis of static balance performance and dynamic postural priority according to playing position in elite soccer players
Reference: Gait Posture. 2019 Sep 5;74:148-153. doi: 10.1016/j.gaitpost.2019.09.008. [Epub ahead of print]
Authors: Jadczak Ł, Grygorowicz M, Wieczorek A, Śliwowski R
Summary: Balance performance and postural priority are important components of motor skill development. No published reports have investigated the differences in static balance abilities and postural priority among professional soccer players according to field position. We hypothesized that static balance as well as dynamic postural priority is influenced by playing position in professional soccer players. The study covered a group of 101 elite professional soccer players who were divided into six subgroups according to playing positions: goalkeepers (G) (n = 10), central defenders (CD) (n = 15), external defenders (ED) (n = 15), central midfielders (CM) (n = 23), external midfielders (EM) (n = 15) and forwards (F) (n = 23). All participants completed the Delos Postural System Test using the standard protocol. The tests were performed unilaterally on non-dominant (NL) and dominant leg (DL) under static conditions (with open and closed eyes) standing on a stable platform and under dynamic conditions on an unstable base. In the static test with open eyes (ST OE) there were no statistically significant differences between the legs and positions. In the static test with closed eyes (ST CE), the differences are statistically significant only between positions. Players on the CM position have significantly higher differences than G. In the dynamic postural priority test (DPPT) there is a difference between positions and legs. In fact, the statistically higher differentiation refers to players in the CM position relative to ED, CD, EM and F. We noticed a significantly greater difference in the NL compared to the DL. Static balance performance and postural priority varied with playing position in elite soccer players. Midfield players have better postural priority than players in other positions. Professional soccer players present greater balance postural priority on the non-dominant leg.

#6 Contextual Factors Influencing External and Internal Training Loads in Collegiate Men's Soccer
Reference: J Strength Cond Res. 2019 Sep 12. doi: 10.1519/JSC.0000000000003361. [Epub ahead of print]
Authors: Curtis RM, Huggins RA, Benjamin CL, Sekiguchi Y, Adams WM, Arent SM, Jain R, Miller SJ, Walker AJ, Casa DJ
Summary: This study investigated factors influencing training loads (TL) in collegiate men's soccer. Total distance, high-speed running distance (>14.4 km·h), high-intensity heart-rate zone duration (HI HRZ, >70% heart rate relative to maximum), and session rating of perceived exertion were assessed daily from 107 male soccer players competing for 5 National Collegiate Athletics Association Division I teams. Differences between athlete role (starter and reserve), position (defender, midfielder, and forward), season phase (preseason, in-season, and postseason), days relative to match (MD-1 to MD-5+), days between matches (<4, 4-5, >5 days), previous match outcome (win, loss, and draw), and upcoming opponent relative ranking (weaker, trivial, and stronger) were examined. Mean differences (MD) and effect sizes (ESs) with 90% confidence intervals were reported. There were trivial and insignificant differences by player role, position, or upcoming opponent strength, and small-moderate increases in preseason TL compared with in-season (ES [range] = 0.4-0.9). TLs were lower for MD-1 and higher for MD-5+ (ES [range] = 0.4-1.3) when compared with MD-2-4. External loads (ES = -0.40 ± 0.20) were less after wins compared with losses. TLs are increased in the preseason, when training sessions occur greater than 5 days from a match and after losses. Contextualizing factors affecting TLs has implications for developing workload prescription and recovery strategies.

#7 The isokinetic strength profile of semi-professional soccer players according to low back pain
Reference: J Back Musculoskelet Rehabil. 2019 Aug 30. doi: 10.3233/BMR-171109. [Epub ahead of print]
Authors: Madić D, Obradović B, Golik-Perić D, Marinković D, Trajković N, Gojković Z
Summary: Soccer as a sport has a very high injury rate and low back pain (LBP) is considered to be the most common overuse injury typically occurring in the back and spine in elite soccer players. The objective was to investigate differences in knee muscle strength and muscle imbalances in soccer players according to lower back pain. One hundred and thirty-six male professional soccer players (20.49 ± 3.73 years, 76.57 ± 8.24 kg, 182.63 ± 6.73 cm) volunteered for the study. The isokinetic dynamometer PrimaDOC (EASYTECH, Italy) was used to assess the hamstring and quadriceps strength at the selected speeds of 60∘/s, whereas the Roland-Morris Disability Questionnaire (RDQ) was used as a health status measure to assess physical disability caused by low back pain. A univariate analysis of variance has shown that there is a statistically significant difference among the groups divided into Absolut peak torque right knee flexors, Absolut peak torque left knee flexors, Ratio between hamstrings and quadriceps strength right leg, Ratio between hamstrings and quadriceps strength left leg based on the RDQ scores. On the other hand, no other significant differences among the groups were found in other parameters. The current study indicates that knee muscle strength variables, resulting from an isokinetic testing, have the potential to discriminate between soccer players with and without a history of low back pain. However, low back pain is a multidimensional phenomenon and knee muscle strength or imbalance alone cannot be expected to explain low back pain.

#8 Physical Performance During Soccer-7 Competition and Small-Sided Games in U12 Players
Reference: J Hum Kinet. 2019 Jul 5;67:281-290. doi: 10.2478/hukin-2018-0082. eCollection 2019 Jun.
Authors: Sanchez-Sanchez J, Sanchez M, Hernández D, Gonzalo-Skok O, Casamichana D, Ramirez-Campillo R, Nakamura FY
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Summary: The aim of this study was to compare the activity profile (external loads) during soccer-7 competition versus 6 vs 6 small-sided games ( SSGs) in U12 players. Peak velocity (Vmax), total distance completed (DT), total distance relative to match duration, the percentage of DT in acceleration (%DAC) and in deceleration (%DEA), and the percentage of DT at different speeds were recorded. Six types of SSGs were randomly implemented: without pitch orientation-delimitation and with a limit of three ball-contacts per player (3TOU), with no limit of ball-contacts (MAN), with a greater number of players as internal-offensive wildcard players (2WI) or external-offensive wildcard players (4WE); and with pitch orientation-delimitation and crossing the rival goal-line while dribbling the ball without goalkeepers (INV) or using official goalkeepers (GKP). The physical demands of SSGs were compared with the average of two soccer-7 match plays. During soccer-7 match plays a lower %DAC and %DEA (p < 0.05) were observed compared to 2WI, 4WE, INV and GKP, and to INV and GKP, respectively. The Vmax and %HI were greater (p < 0.05) in soccer-7 match plays compared to all SSGs. In conclusion, the demands imposed on U12 players during different formats of SSGs differ from the soccer-7 match play demands, presenting a low stimulation of the actions performed at high-speed and an adequate simulation of acceleration-deceleration actions.

#9 Effects of Slackline Training on Acceleration, Agility, Jump Performance and Postural Control in Youth Soccer Players
Reference: J Hum Kinet. 2019 Jul 5;67:235-245. doi: 10.2478/hukin-2018-0078. eCollection 2019 Jun.
Authors: Fernández-Rio J, Santos L, Fernández-García B, Robles R, Casquero I, Paredes R
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Summary: The goal of this study was to assess the effects of a supervised slackline training program in a group of soccer players. Thirty-four male division I under-19 players (16.64 ± 0.81 years) agreed to participate in the study. They were randomly divided into an experimental group (EG) and a control group (CG). The first group (EG) followed a 6-week supervised slackline training program (3 sessions/week; 5-9 min/session), while the CG performed only regular soccer training. Several variables were assessed in all participants: acceleration (20-m sprint test), agility (90º turns test), jump performance (squat jump, countermovement jump), and postural control (Center of Pressure ( CoP) testing: length, area, speed, Xmean, Ymean, Xspeed, Yspeed, Xdeviation, Ydeviation). Ratings of perceived exertion and local muscle ratings of perceived exertions were also recorded after each slackline training session. At post-tests, there was a significant increase only in the EG in acceleration, agility, squat jump and countermovement jump performance, as well as several CoP variables: area in the bipedal support on a firm surface, and length, area and speed in the left leg on a firm surface. The program was rated as "somewhat hard" by the players, while quadriceps, gastrocnemius and tibialis anterior were the most exerted muscles while slacklining. In conclusion, slackline training can be an effective training tool for young, high-level soccer players.

#10 The Yo-Yo Intermittent Endurance Level 2 Test: Reliability of Performance Scores, Physiological Responses and Overload Characteristics in Competitive Soccer, Basketball and Volleyball Players
Reference: J Hum Kinet. 2019 Jul 5;67:223-233. doi: 10.2478/hukin-2018-0091. eCollection 2019 Jun.
Authors: Papanikolaou K, Chatzinikolaou A, Pontidis T, Avloniti A, Deli CK, Leontsini D, Draganidis D, Tsimeas PD, Rafailakis L, Jamurtas AZ, Krustrup P, Mohr M, Fatouros IG
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Summary: The purpose of this study was to evaluate the reliability and reproducibility of the physiological and overload features of the Yo-Yo intermittent endurance test level 2 (Yo-Yo IE2) in competitive male soccer (n = 20), basketball (n = 11), and volleyball players (n = 10). The participants completed Yo-Yo IE2 tests on three separate occasions with assessment of performance, heart rate, running speed, accelerations, decelerations and body load using GPS instrumentation. The intra-class correlation coefficient index, confidence intervals and coefficients of variation were calculated to assess the reliability of the test. Intra-class correlation coefficients for test-retest trials in the total sample ranged from large to nearly perfect (total distance: 0.896; mean speed: 0.535; maximum speed: 0.715; mean HR: 0.876; maximum HR: 0.866; body load: 0.865). The coefficients of variation for distance, mean speed, HR response, as well as acceleration and deceleration scores for test-retest trials ranged from 1.2 to 12.5% with no differences observed among particular sport disciplines. The CV for shuttles performed ranged from 4.4 to 5.5% in all sports. Similar results were obtained for the three different categories of players tested. These results suggest that the Yo-Yo IE2 test appears to be a reliable alternative for evaluating the ability to perform intermittent high-intensity running in different outdoor and indoor team sports. Players may need one or two familiarization tests to ensure valid assessment of intermittent endurance capacity. It appears that the Yo-Yo IE2 test incorporates accelerations and decelerations in a consistent and reproducible fashion.

#11 Repeated Sprint Ability in Youth Soccer Players: Independent and Combined Effects of Relative Age and Biological Maturity
Reference: J Hum Kinet. 2019 Jul 5;67:209-221. doi: 10.2478/hukin-2018-0090. eCollection 2019 Jun.
Authors: Duarte JP, Coelho-E-Silva MJ, Costa D, Martinho D, Luz LGO, Rebelo-Gonçalves R, Valente-Dos-Santos J, Figueiredo A, Seabra A, Malina RM
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Summary: The objective of the study was to examine the effects of the relative age effect (RAE) and predicted maturity status on body size and repeated sprint ability (RSA: 7 x 34.2 m / 25 s interval) in youth soccer. The sample was composed of 197 male players aged 13-14 years. Body mass, stature, and sitting height were measured, RSA was assessed in the field, and age at peak height velocity (APHV) was predicted. Factorial ANOVA tested the independent and combined effects of RAE given by birth quarters (BQs) and maturity status on dependent variables. Players born in the second birth quarter (BQ2) were significantly taller (F = 4.28, p < 0.01) than their peers born in BQ1 and BQ3. Additionally, players born in BQ2 performed better than players born in BQ4 in RSA total time and ideal time (F ranged between 4.81 and 4.90, p < 0.01), while players born in BQ1 exhibited a lower RSA fatigue index compared to those born in BQ4 (F = 2.90, p < 0.05). The interaction of the BQ and maturity status was a significant source of inter-individual variation for body size (F ranged between 64.92 and 105.57; p < 0.01) and RSA output (F ranged between 4.082 and 6.76; p < 0.05). In summary, being relatively older and, simultaneously, advanced in maturity status corresponds to a substantial advantage in characteristics that are related to soccer-specific fitness.





Latest research in football - week 38 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Longitudinal emotional process among adolescent soccer player in intensive training centre
Reference: J Sports Sci. 2019 Sep 9:1-12. doi: 10.1080/02640414.2019.1662538. [Epub ahead of print]
Authors: Saby Y, Pupier Y, Guillet-Descas E, Nicolas M, Martinent G
Summary: Grounded in Lazarus's (1999) cognitive motivational relational theory of emotions, this study aimed to explore longitudinal relationships between appraisals, everyday emotions related to the competitive environment and emotional regulation strategies during a competitive season. Forty adolescent soccer players (Mage = 15.8) involved in an intensive training centre from a professional club voluntarily participated to the study. A series of hierarchical linear modelling analyses were conducted upon the 9 measurement times to: (a) examine the relationships between appraisals (threat, challenge, loss), pleasant (happiness, excitement) and unpleasant (anxiety, dejection, anger) emotions, and emotional regulation strategies (adaptive and less adaptive); and (b) ascertain whether the relationships between appraisals and emotions were mediated by emotion regulation strategies. The results of the random coefficient regression models showed: (a) positive relationships between challenge appraisal, adaptive emotion regulation, and pleasant emotions as well as between threat and loss appraisals, less adaptive emotion regulation and unpleasant emotions; and (b) mediating effects of emotional regulation strategies in the appraisals - emotions relationships. As a whole, this study furthered knowledge base about the competitive environment in showing that appraisals, emotion regulation and emotions are intertwined psychological constructs in a dynamic relationship allowing athletes to continuously adjust to their constantly changing everyday demands.

#2 Artificial-turf surfaces for sport and recreational activities: microbiota analysis and 16S sequencing signature of synthetic vs natural soccer fields
Reference: Heliyon. 2019 Aug 29;5(8):e02334. doi: 10.1016/j.heliyon.2019.e02334. eCollection 2019 Aug.
Authors: Valeriani F, Margarucci LM, Gianfranceschi G, Ciccarelli A, Tajani F, Mucci N, Ripani M, Romano Spica V
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Summary: Synthetic fibres are used in place of the natural grass worldwide, for realizing playgrounds, soccer fields and even domestic gardens or recreational structures. An intensive use of artificial turf is currently observed in sports facilities, due to lower costs, higher sustainability in recycling of materials, and advantages related to athletic practice and performance. However, even if chemical and physical risks were studied, the microbiological component was not fully addressed, especially considering a comprehensive evaluation of the microbiota in synthetic vs natural playground surfaces. Here, we investigated the microbial community present on soccer fields, using Next Generation Sequencing and a 16S amplicon sequencing approach. Artificial and natural turfs show own ecosystems with different microbial profiles and a mean Shannon's diversity value of 2.176 and 2.475, respectively. The bacterial community is significantly different between facilities (ANOSIM: R = 0.179; p < 0.001) and surface materials (ANOSIM: R = 0.172; p < 0.005). The relative abundance of potentially pathogenic bacterial OTUs was higher in synthetic than in natural samples (ANOVA, F = 2.2). Soccer fields are characterized by their own microbiota, showing a different 16S amplicon sequencing signature between natural and artificial turfs.

#3 The Running and Technical Performance of U13 to U18 Elite Japanese Soccer Players During Match Play
Reference: J Strength Cond Res. 2019 Sep 6. doi: 10.1519/JSC.0000000000003300. [Epub ahead of print]
Authors: Goto H, Saward C
Summary: The aims of the current study were (a) to examine age-related differences in match running performance with 2 different approaches (speed vs. metabolic power) in U13-U18 Japanese elite soccer players and (b) to examine age-related differences in technical match performance in U13-U18 Japanese elite soccer players. Participants were 110 outfield players from academies of 2 professional soccer clubs in Japan. Forty-eight 11-a-side official league matches (13, 6, 9, 7, 6, and 7 matches for U13, U14, U15, U16, U17, and U18 age-groups, respectively) were analyzed (152 complete match files). Global positioning system (15 Hz) and video analysis were used to analyze running and technical performance during matches, respectively. Total distance covered in absolute terms (U13 < [U14 and U15] < [U16-U18]; p < 0.05 for all), high-intensity running distance ([U13-U15] < [U16-U18]; p < 0.05 for all), and distance covered during the metabolic power zone of ≥35 W·kg relative to match playing time ([U13 < U16], [U13-U15] < [U17 and U18]; p < 0.05 for all) increased with age. The speed zone based approach (high-intensity running distance, ≥4.0 m·s) underestimated high-intensity demands compared with the metabolic power zone based approach (≥20 W·kg) by ∼33 to ∼57% (p < 0.01 for all), with the underestimation declining with age (p < 0.001). Pass accuracy improved with age from 73% at U13 to 85% at U18 (p < 0.001). Therefore, distance covered at high speeds and at high metabolic powers, and pass accuracy increase with age. Moreover, the speed zone based approach underestimates the demands of match play in Japanese elite youth soccer players. The current results could support coaches to develop players, identify talent, and produce age-specific training programs.

#4 The Reliability of Potential Fatigue-Monitoring Measures in Elite Youth Soccer Players
Reference: J Strength Cond Res. 2019 Sep 6. doi: 10.1519/JSC.0000000000003317. [Epub ahead of print]
Authors: Fitzpatrick JF, Hicks KM, Russell M, Hayes PR
Summary:  Monitoring fatigue is of vital importance to practitioners; however, logistics and concerns about reliability may impede the use of certain measures. This study aimed to quantify the reliability of potential measures of fatigue; a subjective wellness questionnaire, jump performance tests, and tri-axial accelerometer variables derived during submaximal shuttle running in elite youth soccer players. A secondary aim was to establish the minimum test duration that could be used for the submaximal shuttle run while maintaining good reliability. Seventeen male youth team players (age: 17.4 ± 0.5 years) were assessed on 2 occasions, spaced 7 days apart. Typical error, coefficient of variation (CV%), interclass correlation (ICC), and minimum detectable change were calculated for a subjective wellness questionnaire, countermovement jump (CMJ), squat jump (SJ) and drop jump contact time (DJ-CT), drop jump height (DJ-JH), and reactive strength (DJ-RSI). A novel submaximal shuttle running test was also used to assess tri-axial accelerometer data reliability. Results suggest that CMJ, SJ, DJ-CT, and DJ-RSI have good test-retest reliability (CV% = 4.5-7.7; ICC = 0.80-0.88); however DJ-JH did not show acceptable reliability (CV% = 6.0; ICC = 0.76). Good reliability was found for all tri-axial accelerometer variables during a 3-minute (2-minute analysis) submaximal shuttle run (CV% = 2.4-8.0; ICC = 0.81-0.95), except for % PlayerLoad anterior-posterior (%PLAP) (CV% = 7.2; ICC = 0.63). The subjective wellness questionnaire demonstrated poor reliability for all items (CV% = 11.2-30.0; ICC = 0.00-0.78). The findings from this study provide practitioners with valuable information about the reliability of a range of potential fatigue-monitoring measures. This can be used to help make accurate decisions about the magnitude of change in these assessments when used in practice.

#5 Effects of a blocked versus an alternated sequence of balance and plyometric training on physical performance in youth soccer players
Reference: BMC Sports Sci Med Rehabil. 2019 Sep 2;11:18. doi: 10.1186/s13102-019-0131-y. eCollection 2019.
Authors: Muehlbauer T, Wagner V, Brueckner D, Schedler S, Schwiertz G, Kiss R, Hagen M
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Summary: The sequence of blocked balance training (BT) followed by blocked plyometric training (PT) showed greater improvements in physical performance than vice versa and is explained by a preconditioning effect of BT-related adaptations on subsequent adaptations induced by PT. However, it remains unclear whether beneficial effects can also be induced using alternating instead of blocked BT and PT exercise sequences. Thus, we examined the effects of a blocked versus an alternated sequence of BT and PT on physical performance in trained individuals. Twenty young soccer players (13 years) were randomly assigned to a blocked (n = 10) or an alternated (n = 10) intervention group. Both groups trained balance and plyometric exercises for six weeks (two sessions/week). The exercises were conducted in a blocked (three weeks of BT followed by three weeks of PT) or an alternated sequence (weekly change of BT and PT). Assessment of pre- and post-training performance included measures of balance, muscle power, speed, and agility. Mainly significant main effects of Test (i.e., pre- to post-test improvements) were observed for the Y-balance test (p ≤ 0.014, 1.3 ≤ Cohen's d ≤ 1.81), the squat jump (p = 0.029, d = 1.36), the countermovement jump (p = 0.002, d = 2.21), the drop jump (p = 0.004, d = 1.96), the split times/total time over 15-m sprinting (p ≤ 0.001, 2.02 ≤ d ≤ 3.08), and the figure-T agility run (p < 0.001, d = 3.80). Further, tendencies toward significant Test x Group interactions were found for several items of the Y-balance test and for SJ height in favor of the blocked BTPT group. Our results indicate that the combined training of balance and plyometric exercises is effective to improve proxies of physical performance in youth soccer players. In addition, there is a limited advantage in some parameters of balance and muscle power for the blocked as compared to the alternated sequence of BT and PT.

#6 Assessment of Selected Exercise-induced CD3+ Cell Subsets and Cell Death Parameters Among Soccer Players
Reference: J Med Biochem. 2019 Mar 26;38(4):437-444. doi: 10.2478/jomb-2019-0013. eCollection 2019 Oct.
Authors: Nowak R, Kostrzewa-Nowak D
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Summary: Molecular mechanisms of biological adaptation to training in professional soccer players are unclear. The aim of this study was to assess the impact of progressive physical effort on peripheral T-cells and their molecular response. Thirteen soccer players form Pogo Szczecin S.A., a top league soccer club, (median age 21, range 18- 31, years old) performed progressive efficiency tests on a mechanical treadmill until exhaustion at the start (period 1) and the end (period 2) of a competition round. Venous blood T-lymphocyte subsets, selected hallmarks of cell death and plasma cytokine levels were determined by flow cytometry three times: pre-exercise, post-exercise, and in recovery. Although significant changes in T, Tc and Tc-naïve cell percentages were found in both periods, Th-naïve cell percentages were altered only in period 1. Post-exercise IL-10 plasma levels were higher than pre-exercise, while an increase in TNF-α levels was noticed in recovery from both periods. An increase in recovery IL-12p70 levels was observed in the second period. Increases in the percentage of T-cells with disrupted mitochondrial membrane potentials, elevated levels of phosphorylated H2AX histones and increases in early apoptotic T-cells were also observed. The immune system in soccer players creates space for naïve CD3+CD8+ cells by inducing mechanisms of cell death. It seems that the cumulative effect of physical activity during a competition round induced an adaptive mechanism, since the cell death process was induced faster during period 2.

#7 Clustering algorithm for formations in football games
Reference: Sci Rep. 2019 Sep 11;9(1):13172. doi: 10.1038/s41598-019-48623-1.
Authors: Narizuka T, Yamazaki Y
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Summary: In competitive team sports, players maintain a certain formation during a game to achieve effective attacks and defenses. For the quantitative game analysis and assessment of team styles, we need a general framework that can characterize such formation structures dynamically. This paper develops a clustering algorithm for formations of multiple football (soccer) games based on the Delaunay method, which defines the formation of a team as an adjacency matrix of Delaunay triangulation. We first show that heat maps of entire football games can be clustered into several average formations: "442", "4141", "433", "541", and "343". Then, using hierarchical clustering, each average formation is further divided into more specific patterns (clusters) in which the configurations of players are different. Our method enables the visualization, quantitative comparison, and time-series analysis for formations in different time scales by focusing on transitions between clusters at each hierarchy. In particular, we can extract team styles from multiple games regarding the positional exchange of players within the formations. Applying our algorithm to the datasets comprising football games, we extract typical transition patterns of the formation for a particular team.

#8 Effects of Temporary Numerical Imbalances on Collective Exploratory Behavior of Young and Professional Football Players
Reference: Front Psychol. 2019 Aug 27;10:1968. doi: 10.3389/fpsyg.2019.01968. eCollection 2019.
Authors: Canton A, Torrents C, Ric A, Gonçalves B, Sampaio J, Hristovski R
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Summary: The aim of this study was to explore how the use of temporary numerical imbalances during small-sided Game SSGs affects team's exploratory behaviors (i.e., variety and quantity of responses given in an ever-changing game context and its rate of change) in different age groups. Two different age groups (under-15 and under-23) of football players participated in the study. For each age group, three teams of five players played six small-sided games of 5 min duration in different conditions: (i) numerical balance (GK + 4 vs. 4 + GK); (ii) temporary numerical imbalance, which consisted of a numerical change of teammates and opponents every one minute. Latitude and longitude GPS coordinates were used to determine the positioning-derived variables. The dynamic overlap (i.e. the measure of average similarity of the game patterns that take place in increasingly larger time intervals) was used to provide information of the rate and breadth of exploratory behavior. The results revealed that the long-term exploratory breadth increased for the under-23 age group. Non-clear effects were found for the short-term rate of exploration, but with an increasing trend. In the under-15 group, the exploratory behavior was more likely to increase in the long term. The increase for the short-term rate of exploration was unclear, but it follows an increasing trend. These results suggest that the use of temporary numerical imbalances could offer coaches more dynamic training situations and different adaptive training environments similar to matches.

#9 Correction to: Injury Incidence, Prevalence and Severity in High-Level Male Youth Football: A Systematic Review
Reference: Sports Med. 2019 Sep 9. doi: 10.1007/s40279-019-01182-x. [Epub ahead of print]
Authors: Jones S, Almousa S, Gibb A, Allamby N, Mullen R, Andersen TE, Williams M
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#10 The association between watching football matches and the risk of cardiovascular events: A meta-analysis
Reference: J Sports Sci. 2019 Sep 9:1-9. doi: 10.1080/02640414.2019.1665246. [Epub ahead of print]
Authors: Lin LL, Gu HY, Yao YY, Zhu J, Niu YM, Luo J, Zhang C
Summary: The aim was to comprehensively shed light on whether viewing football games is associated with a higher risk of cardiovascular disease (CVD). Electronic databases were searched through 17 May 2018. All studies focusing on the association between viewing football matches and the fatal or non-fatal CVD were identified. Viewing football matches was associated with a higher risk of fatal overall CVD (RR: 1.06, 95%CI: 1.01-1.12) in both men (RR: 1.13, 95%CI: 1.004-1.28) and women (RR: 1.08, 95%CI: 1.01-1.15). Subgroup analysis showed that failure of the team has a higher risk of fatal overall CVD (RR: 1.29, 95%CI: 1.15-1.45). However, lower risk of fatal overall CVD from spectators was observed when team obtained a victory (RR: 0.80, 95%CI: 0.66-0.96). For non-fatal CVD, viewing football matches was associated with a higher risk of non-fatal overall CVD (RR: 1.24, 95%CI: 1.09-1.41) in both men (RR: 1.73, 95%CI: 1.12-2.69) and women (RR: 1.25, 95%CI: 1.08-1.45). Subgroup analysis showed that viewing football matches was associated with a higher risk of non-fatal myocardial infarction (RR: 1.20, 95%CI: 1.04-1.38) in both men and women (RR: 1.51, 95%CI: 0.99-2.28; RR: 1.21, 95%CI: 1.08-1.36, respectively). No significant increase was found in fatal or non-fatal stroke. Viewing football matches was associated with a higher risk of the fatal and non-fatal CVD, especially in male spectators. The victory of team could have a lower risk of fatal CVD. Therefore, precautionary measures should be required for the reduction of healthcare burden in football matches.

#11 Effect of poor cooperation between coaching and medical staff on muscle re-injury in professional football over 15 seasons
Reference: Open Access J Sports Med. 2019 Aug 5;10:107-113. doi: 10.2147/OAJSM.S221292. eCollection 2019.
Authors: Ghrairi M1,2,3, Loney T1, Pruna R2,4, Malliaropoulos N2,5, Valle X2,4.
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Summary: Muscle injury is the most common type of injury in football. Previous research has focused on traditional risk factors (eg, age, injury history, muscle imbalance/inflexibility) contributing to muscle re-injury. The effect of poor cooperation between the coaching and medical teams on the risk of re-injury remains unexplored in the sports medicine football literature. Examine the effect of poor cooperation between coaching and medical teams on muscle re-injury in professional football. Retrospective review of the medical files of 97 footballers of a professional team in Dubai over 15 consecutive seasons (2002-2017). Medical team recorded all injuries in each player's file. Data on the perceived level of cooperation between coaching and medical teams were available in the daily meeting notes from the head of the medical team. The level of perceived cooperation was ranked on a three-point Likert scale by the head of the medical team and depended on whether the coaching team accepted the player injury (excellent cooperation), brought some suggestion after discussion with the medical team (normal cooperation) or rejected it (poor cooperation). In total, 338 indirect muscle injuries (21 re-injuries) were recorded during 15 consecutive seasons., There was a significant increase in the mean number of total injuries (mean ± SE, 95% CI; 16±2, 12-21; P<0.0001), mean number of indirect muscle injuries (12±1, 95% CI 10-14; P<0.0001), and indirect muscle re-injuries (4±1, 95% CI 3-5; P<0.0001) during seasons with a poor perceived level of cooperation compared to seasons with a normal/excellent perceived level of cooperation. Findings suggest that poor cooperation between coaching and medical teams may increase the risk of muscle re-injury in professional football. Future studies conducted in different clubs, leagues, countries, and even sports are required to further explore the effect of cooperation between coaching and medical teams on the risk of re-injury.





Latest research in football - week 37 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 A Single Session of Straight Line and Change-of-Direction Sprinting per Week Does Not Lead to Different Fitness Improvements in Elite Young Soccer Players
Reference: J Strength Cond Res. 2019 Sep 2. doi: 10.1519/JSC.0000000000003369. [Epub ahead of print]
Authors: Beato M, Bianchi M, Coratella G, Merlini M, Drust B
Summary: Effective prescription is especially important in elite soccer players, who have a very limited time to dedicate to specific physical development as a consequence of factors such as congested match schedules and travel. The aim of this study was to compare the effectiveness of one repeated-sprint training (RST) session per week over an 8-week period on physical performance. A second aim was to compare the effect of RST involving straight sprints (RST-SS) or changes of direction (RST-COD). This study used a randomized pre-post parallel group trial design. The elite soccer players were randomly assigned to either an RST-SS (10 players) or RST-COD (10 players). RST-SS was 3 sets of 7 × 30-m sprints with 20-second and 4-minute recovery between sprints and sets, respectively. RST-COD was 3 sets of 7 × 20 + 20 m (one COD of 180°) shuttle sprints with 20-second and 4-minute recovery between sprints and sets, respectively. The physical tests selected were long jump, repeated-sprint ability (RSA) best, RSA mean, 505 agility test, Yo-Yo recovery level 1, 10, 30, and 40 m sprints. RST-SS reported unclear variations in long jump, sprint 30 m, sprint 40 m, RSA best, and RSA mean, whereas RST-COD showed unclear and trivial variations in sprint 10 m, sprint 30 m, sprint 40 m, RSA best, and RSA mean. The between-group analysis did not report any statistical difference. In conclusion, a single session of RST-SS and RST-COD do not improve soccer-specific fitness indicators in elite youth players during the season.

#2 The Effects of Six-Weeks Change of Direction Speed and Technique Modification Training on Cutting Performance and Movement Quality in Male Youth Soccer Players
Reference: Sports (Basel). 2019 Sep 6;7(9). pii: E205. doi: 10.3390/sports7090205.
Authors: Dos'Santos T, McBurnie A, Comfort P, Jones PA
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Summary: Cutting manoeuvres are important actions associated with soccer performance and a key action associated with non-contact anterior cruciate ligament injury; thus, training interventions that can improve cutting performance and movement quality are of great interest. The aim of this study, therefore, was to determine the effects of a six-week change of dire[ction (COD) speed and technique modification training intervention on cutting performance and movement quality in male youth soccer players (U17s, n = 8) in comparison to a control group (CG) (U18s, n = 11) who continued 'normal' training. Cutting performance was assessed based on completion time and COD deficit, and the field-based cutting movement assessment score (CMAS) qualitative screening tool was used to assess cutting movement quality. Significant main effects for time (pre-to-post changes) (p ≤ 0.041, η2 = 0.224-0.839) and significant interaction effects of time and group were observed for cutting completion times, COD deficits, and CMASs. Improvements in completion time (p < 0.001, g = 1.63-1.90, -9% to -11% vs. -5% to 6%) and COD deficit (p ≤ 0.012, g = -1.63 to -2.43, -40-52% vs. -22% to -28%) for the COD intervention group (IG) were approximately two-times greater than the CG. Furthermore, lower CMASs (i.e., improved cutting movement quality) were only observed in the IG (p ≤ 0.025, g = -0.85 to -1.46, -23% to -34% vs. 6-19%) compared to the CG. The positive changes in CMASs were attributed to improved cutting technique and reduced incidences of high-risk deficits such as lateral trunk flexion, extended knee postures, knee valgus, hip internal rotation, and improved braking strategies. The results of this study indicate that COD speed and technique modification training, in addition to normal skills and strength training, improves cutting performance and movement quality in male youth soccer players. Practitioners working with male youth soccer players should implement COD speed and technique modification training to improve cutting performance and movement quality, which may decrease potential injury-risk.

#3 Comparing Balance Control Between Soccer Players and Non-Athletes During a Dynamic Lower Limb Reaching Task
Reference: Res Q Exerc Sport. 2019 Sep 3:1-6. doi: 10.1080/02701367.2019.1649356. [Epub ahead of print]
Authors: Snyder N, Cinelli M
Summary: Balance control is an essential element of locomotion that enhances biomotor abilities and physical performance. Individuals with extensive soccer experience display superior static single leg balance control compared to athletes of other sports as well as non-athletes. However, during a match, players often encounter greater challenges to single leg balance that require rapid decision-making skills and dynamic stability. The purpose of this study was to determine if individuals with extensive soccer training demonstrate superior single-leg balance control compared to non-athletes during a dynamic lower limb reaching task. 22 varsity soccer players were matched with 21 non-athlete controls. Single-leg balance control was assessed during a Go/No-Go lower limb reaching task. Centre of pressure displacement (dCOP) was measured for both the dominant and non-dominant feet and compared between groups. Soccer players displayed reduced dCOP during All Go trials compared to non-athletes, particularly in the medial-lateral plane. Additionally, soccer players displayed reduced anterior-posterior dCOP during Go/No-Go trials compared to non-athletes, particularly on their dominant foot. Athletes with soccer-specific training demonstrate improved executive control and use of proprioceptive information, which results in an improved ability to maintain single-support balance and corral COP during a dynamic visuomotor lower limb-reaching task. As such, balance training may be a useful addition to athlete training regimes to improve sport-specific performance. Future research would compare these results to athletes of other sports to explore balance control during a visuomotor reaching task and how it may differ based on sport training history.

#4 Lactate Equivalent for Maximal Lactate Steady State Determination in Soccer
Reference: Res Q Exerc Sport. 2019 Sep 3:1-12. doi: 10.1080/02701367.2019.1643446. [Epub ahead of print]
Authors: Garcia-Tabar I, Rampinini E, Gorostiaga EM
Summary: The association between an overlooked classical Lactate Threshold (LT), named "Minimum Lactate Equivalent" (LEmin), with Maximal Lactate Steady State (MLSS) has been recently described with good MLSS prediction results in endurance-trained runners. This study aimed to determine the applicability of LEmin to predict MLSS in lower aerobic-conditioned individuals compared to well-established blood lactate-related thresholds (BLTs). Fifteen soccer players [velocity at MLSS (MLSSV) 13.2 ± 1.0 km·h-1; coefficient of variation (CV) 7.6%] conducted a submaximal discontinuous incremental running test to determine BLTs and 3-6 constant velocity running tests to determine MLSSV. LEmin did not differ from conventional LTs (p > .05) and was 24% lower than MLSS (p < .001; ES: 3.26). Among LTs, LEmin best predicted MLSSV (r = 0.83; p < .001; SEE = 0.59 km·h-1). There was no statistical difference between MLSS and estimated MLSS using LEmin prediction formula (p = .99; ES: 0.001). Mean bias and limits of agreement were 0.00 ± 0.58 km·h-1 and ±1.13 km·h-1, respectively. LEmin best predicted MLSSV (r = 0.92; p < .001; SEE = 0.54 km·h-1) in the pooled data of soccer players and endurance-trained runners of the previous study (n = 28; MLSSV range 11.2-16.5 km·h-1; CV 9.8%). Results support LEmin to be one of the best single predictors of MLSS. This study is the sole study providing specific operational regression equations to estimate the impractical gold standard MLSSV in soccer players by means of a BLT measured during a submaximal single-session test.

#5 Creative and Intuitive Decision-Making Processes: A Comparison of Brazilian and German Soccer Coaches and Players
Reference: Res Q Exerc Sport. 2019 Sep 3:1-15. doi: 10.1080/02701367.2019.1642994. [Epub ahead of print]
Authors: Klatt S, Noël B, Musculus L, Werner K, Laborde S, Lopes MC, Greco PJ, Memmert D, Raab M
Summary:  The concepts of creativity and intuition have been well studied in isolation, but less is known about their distinctive contributions to option generation in decision making. We examined the relation between creative and intuitive decision making in two studies-one involving coaches and one involving soccer players-using video footage of real soccer matches. Additionally, we analyzed whether this relation is culture generic or culture specific by conducting matched cross-cultural studies in a European and a South American country. In Study 1, results indicate a conceptual overlap of creativity and intuition for Brazilian and German soccer coaches. Furthermore, coaches did not differ in their evaluation of creative and intuitive actions of players of both cultures. In Study 2, we found that for both subsamples the total number of generated options was positively correlated with the quality of the first and the final option and that the quality of players' first (intuitive) option was higher than that of options generated later. Moreover, results indicate a positive correlation between a player's creativity score and the quality of the first generated option for the whole sample. Overall, our findings provide meaningful information regarding athletes' and coaches' option-generation processes in decision making in complex team sports.

#6 Should you let your child play football? What about soccer or hockey?
Reference: Appl Neuropsychol Child. 2019 Sep 2:1-6. doi: 10.1080/21622965.2019.1654385. [Epub ahead of print]
Authors: Ferraro FR, Cuccolo K, Wise RA
Summary: College students (n = 120) answered 18 yes-no questions that varied the child's gender (male, female), grade (grade school, high school, college), and sport (football, soccer, hockey). The format of the 18 yes or no questions was "If you had a child in (grade school, high school, college) would you let (him, her) play (football, soccer, hockey)"? Similar to a previous study, a large percentage (78.8%) of the respondents answered yes to the questions about football, indicating that they would permit their children to play football despite the risk of concussion (96% yes for male children, 67% yes for female children). Although the number of respondents who would allow their male child to play soccer (98% for male children, 99% for female children) or hockey (92% for male children, 89% for female children) was similar to the percentage of respondents that would allow their male child to play football, significantly more respondents would allow their female child to play soccer or hockey than football. This result is potentially problematic because soccer and hockey have high rates of concussion, especially for females, which suggests that the respondents may have been unaware of this fact.

#7 Psychological characteristics in women football players: Skills, mental toughness, and anxiety
Reference: Scand J Psychol. 2019 Sep 6. doi: 10.1111/sjop.12571. [Epub ahead of print]
Authors: Kristjánsdóttir H, Jóhannsdóttir KR, Pic M, Saavedra JM
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Summary: Women's football has been far less studied than men's. This work's objectives were to: (1) analyze the differences in psychological skills, mental toughness (MT), and anxiety in women football players according to their level (national team, first division, and second division); and (2) predict those three levels (using a multivariate model) according to the players' psychological skills, mental toughness, and anxiety. One hundred and forty-two Icelandic women football players (23.5 ± 3.5 years) participated in the study. They were classified into three groups according to their level: national team, and first and second divisions. Three questionnaires were used: the Test of Performance Strategies Questionnaire, the Sport Mental Toughness Questionnaire, and the Sport Anxiety Scale-2 questionnaire. A one-way ANOVA with Bonferroni post hoc correction was used to examine differences between teams. Applying a classification tree analysis, the participants were classified into three groups according to their level. There were few differences between the three groups in psychological skills, but in mental toughness and anxiety the national team had the highest and lowest values respectively, and the first and second division players differed in relaxation in competition (TOPS), total score and confidence (SMTQ), and worry (SAS-2). The classification tree correctly classified 54.9% of the sample with the variables total score (SMTQ) and activation in practice (TOPS). Therefore, given the relevance that psychological attributes appear to have for women football players' performance, it would seem indispensable to incorporate the figure of the sports psychologist into national and club teams.

#8 Different Marks in the Pitch Constraint Youth Players' Performances During Football Small-sided Games
Reference: Res Q Exerc Sport. 2019 Sep 3:1-9. doi: 10.1080/02701367.2019.1645938. [Epub ahead of print]
Authors: Coutinho D, Gonçalves B, Travassos B, Folgado H, Figueira B, Sampaio J

Summary: This study aimed to compare players' performances when manipulating the external markings of the pitch during football small-sided games. Ten under-15 players performed a 5-a-side (plus goalkeepers) under three conditions: (i) Lines, the game was played in a pitch in which the external boundaries were painted with full lines; (ii) Dashed, the game was played in a pitch in which the external boundaries were painted with dashed lines; (iii) Corners, the game was played in a pitch were the external boundaries were delimited by one marker at each pitch corner. Players' positional data was used to compute tactical and time-motion variables. Also, technical analysis was comprised using video footage. Results showed similar tactical, physical and technical performances between the Lines and Dashed conditions. In contrast, the Lines condition showed small higher effects than Corners scenario in the time spent synchronized in longitudinal and lateral displacements, game pace, total distance covered, distance covered while jogging, number successful dribbles and shots on target. The Lines scenario has also revealed a lower effective playing space, distance covered at walking and running and a lower number of passes (small effects) compared to Corners. These results highlight that these changes in informational perception constraints modify players movement behavior. Accordingly, pitches with more visible boundaries were likely to decrease team dispersion, which may optimize team synchrony and technical performances, while decreasing the distance covered at higher speeds. Coaches may use this information to modify the types of pitch external boundaries markings, exposing the players to different environmental information.

#9 Return to play after surgery for isolated unstable syndesmotic ankle injuries (West Point grade IIB and III) in 110 male professional football players: a retrospective cohort study
Reference: Br J Sports Med. 2019 Aug 31. pii: bjsports-2018-100298. doi: 10.1136/bjsports-2018-100298. [Epub ahead of print]
Authors: D'Hooghe P, Grassi A, Alkhelaifi K, Calder J, Baltes TP, Zaffagnini S, Ekstrand J
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Summary: The purpose was to evaluate time to return to play following surgical stabilisation of isolated unstable syndesmosis injuries in a cohort of professional male football players. All professional football players undergoing surgery for isolated unstable syndesmosis injury (West Point grade ≥IIB) at a specialised Orthopaedic and Sports Medicine Hospital were followed up until return to play (minimum ≥6 months). Players with a stable syndesmosis, injuries older than 6 weeks, concomitant medial or lateral malleolar fracture or previous ankle surgery were excluded. During rehabilitation, time required to return to sports-specific rehabilitation, team training and first match play, were recorded. Between January 2012 and December 2017, a total of 110 male professional football players were included. The mean time required to begin on field rehabilitation was 37±12 days, while the mean time to return to team training was 72±28 days. The first official match was played on average 103±28 days postoperatively. Multivariable analysis revealed that the severity of injury, the concomitant presence of talar cartilage injury and the age of the player were significantly associated (p<0.00001) with time to return to on field rehabilitation, team training and match play. In this cohort of professional football players, surgical stabilisation of isolated unstable syndesmosis injuries (West Point grade ≥IIB) allowed for relatively quick return to play. High grade injury (West Point grade III), concomitant cartilage injury and greater age were associated with longer return to play times.

#10 Blood Biomarkers of Recovery Efficiency in Soccer Players
Reference: Int J Environ Res Public Health. 2019 Sep 6;16(18). pii: E3279. doi: 10.3390/ijerph16183279.
Authors: Nowakowska A, Kostrzewa-Nowak D, Buryta R, Nowak R
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Summary: Physical exercise strongly affects human metabolism and causes biochemical changes. This study aimed to investigate the relationship between routine plasma biomarker levels and recovery efficiency in soccer players during an entire competitive match season. The players participating in the study were divided into a midfielder/defender group (seven midfielders and seven defenders) and a goalie/substitute group (six persons-goalkeepers and players with a short cumulative match-time). The fasting capillary blood samples were taken 17-24 h after each competitive match. The blood plasma was used to determine the creatinine, urea, alkaline phosphatase, creatine kinase, lactate dehydrogenase, aspartate and alanine aminotransferase, iron and magnesium levels of the athletes. The levels of (AST) (aspartate aminotransferase), (ALT) (alanine aminotransferase) and (Cr) creatinine were higher in the midfielder/defender group than in the control group, but only AST and Cr significantly varied over time (AST decreased, and Cr increased with time). The (LDH) (lactate dehydrogenase) activity and urea level were significantly lower in the midfielder/defender group than in the goalie/substitute group, and it significantly varied over time (LDH decreased, and urea increased with time). No differences in the (CK) creatine kinase and (ALP) alkaline phosphatase activities between the groups was found, although CK increased significantly with time in the midfielder/defender group (particularly midfielders in the spring round). In midfielders, the AST activity and the iron level were significantly lower in the spring than in the autumn round. On the contrary, ALT, CK, urea and magnesium levels were significantly higher in the spring than in autumn round. A long-term measurement of biochemical parameters in elite soccer players indicated that AST, CK, LDH and creatinine levels, when analyzed together, could constitute a useful set of markers for monitoring recovery periods.

#11 Effect of Pre-training and Post-training Nordic Exercise on Hamstring Injury Prevention, Recurrence, and Severity in Soccer Players
Reference:  Ann Rehabil Med. 2019 Aug;43(4):465-473. doi: 10.5535/arm.2019.43.4.465. Epub 2019 Aug 31.
Authors: Elerian AE, El-Sayyad MM, Dorgham HAA
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Summary: The purpose was to investigate the effect of adding Nordic exercise as post-training in decreasing hamstring initial, recurrent injuries rates, and their severity. In this randomly controlled trial study, 34 professional football players aged 21 to 35 years were randomly assigned into two groups (17 players each) from Sporting clubs at Alexandria, Egypt. For group one, Nordic hamstring exercise (NHE) was performed pre-training and post-training. For group two, NHE was only performed pre-training. The control group was the same team during the previous season. Length of the trial was 12 weeks. The Australian football association injury form was used to collect incidence of injuries for each subject in both groups. Pooled results based on total injuries showed that group one had significantly less hamstring initial injuries (92% less) than the previous season, while group two had 80% less initial injuries and 85% less recurrent injuries than previous season. Regarding the severity of injuries in term of mean number of absent days, it was 1 day for group one and 2.7 days for group two while it was 7.95 days for the previous season during total risk time of 116.3±13.2 and 117.6±5.7 exposure hours for group one and group two, respectively. The use of NHE as a prevention protocol was effective in reducing all hamstring injuries with the use of NHE during pre-training and post-training having the greatest effect.

#12 Pressure pain sensitivity over nerve trunk areas and physical performance in amateur male soccer players with and without chronic ankle instability
Reference: Phys Ther Sport. 2019 Sep 4;40:91-98. doi: 10.1016/j.ptsp.2019.09.002. [Epub ahead of print]
Authors: Navarro-Santana MJ, Albert-Lucena D, Gómez-Chiguano GF, Plaza-Manzano G, Fernández-de-Las-Peñas C, Cleland J, Pérez-Silvestre Á, Asín-Izquierdo I
Summary: Chronic ankle instability (CAI) is reported after ankle sprain. Our aim was to assess differences in mechanical pain sensitivity of lower extremity nerve trunks and physical performance between amateur soccer players with and without CAI. Fifty-five male soccer players, 28 with and 27 without CAI participated in this stud. The perceived instability was assessed with the Cumberland Ankle Instability Tool (CAIT). Pressure pain thresholds (PPTs) on the common peroneal and tibialis nerve trunks, vertical jump, lateral step-down test and joint position sense of the knee were assessed by a blinded assessor.Soccer players with CAI showed lower PPTs over the common peroneal nerve than those without CAI (between-groups mean difference: 1.0 ± 0.8 kg/cm2, P < 0.001). No differences for PPT over the tibialis posterior (P = 0.078) or any physical performance outcome (knee joint positioning sense [P = 0.798], lateral step-down test [P = 0.580] and vertical jump variables [all, P > 0.310]) were found. PPT over the common peroneal nerve exhibited a significant moderate correlation with the CAIT score (r = 0.528, P < 0.001).Amateur soccer players with CAI have higher pressure pain sensitivity over the common peroneal nerve but exhibit similar physical performance to amateur soccer players without CAI.





Latest research in football - week 36 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Combined Resistance and Plyometric Training Is More Effective Than Plyometric Training Alone for Improving Physical Fitness of Pubertal Soccer Players
Reference: Front Physiol. 2019 Aug 7;10:1026. doi: 10.3389/fphys.2019.01026. eCollection 2019.
Authors: Zghal F, Colson SS, Blain G, Behm DG, Granacher U, Chaouachi A
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Summary: The purpose of this study was to compare the effects of combined resistance and plyometric/sprint training with plyometric/sprint training or typical soccer training alone on muscle strength and power, speed, change-of-direction ability in young soccer players. Thirty-one young (14.5 ± 0.52 years; tanner stage 3-4) soccer players were randomly assigned to either a combined- (COMB, n = 14), plyometric-training (PLYO, n = 9) or an active control group (CONT, n = 8). Two training sessions were added to the regular soccer training consisting of one session of light-load high-velocity resistance exercises combined with one session of plyometric/sprint training (COMB), two sessions of plyometric/sprint training (PLYO) or two soccer training sessions (CONT). Training volume was similar between the experimental groups. Before and after 7-weeks of training, peak torque, as well as absolute and relative (normalized to torque; RTD r ) rate of torque development (RTD) during maximal voluntary isometric contraction of the knee extensors (KE) were monitored at time intervals from the onset of contraction to 200 ms. Jump height, sprinting speed at 5, 10, 20-m and change-of-direction ability performances were also assessed. There were no significant between-group baseline differences. Both COMB and PLYO significantly increased their jump height (Δ14.3%; ES = 0.94; Δ12.1%; ES = 0.54, respectively) and RTD at mid to late phases but with greater within effect sizes in COMB in comparison with PLYO. However, significant increases in peak torque (Δ16.9%; p < 0.001; ES = 0.58), RTD (Δ44.3%; ES = 0.71), RTD r (Δ27.3%; ES = 0.62) and sprint performance at 5-m (Δ-4.7%; p < 0.001; ES = 0.73) were found in COMB without any significant pre-to-post change in PLYO and CONT groups. Our results suggest that COMB is more effective than PLYO or CONT for enhancing strength, sprint and jump performances.

#2 Training/Match External Load Ratios in Professional Soccer Players: A Full-Season Study
Reference: Int J Environ Res Public Health. 2019 Aug 23;16(17). pii: E3057. doi: 10.3390/ijerph16173057.
Authors: Clemente FM, Rabbani A, Conte D, Castillo D, Afonso J, Truman Clark CC, Nikolaidis PT, Rosemann T, Knechtle B
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Summary: The aim of this study was two-fold: (i) to describe the training/match ratios of different external load measures during a full professional soccer season while analyzing the variations between different types of weeks (three, four and five training sessions/week) and (ii) to investigate the relationship between weekly accumulated training loads and the match demands of the same week. Twenty-seven professional soccer players (24.9 ± 3.5 years old) were monitored daily using a 10-Hz global positioning system with a 100-Hz accelerometer. Total distance (TD), running distance (RD), high-speed running (HSR), sprinting distance (SD), player load (PL), number of high accelerations (ACC), and number of high decelerations (DEC) were recorded during training sessions and matches. An individual training/match ratio (TMr) was calculated for each external load measure. Weeks with five training sessions (5dW) presented meaningfully greater TMr than weeks with four (4dW) or three (3dW) training sessions. Additionally, TDratio (TDr) was significantly greater in 5dW than in 3dW (mean differences dif: 1.23 arbitray units A.U.) and 4dW (dif: 0.80 A.U.); HSRr was significantly greater in 5dW than in 3dW (dif: 0.90 A.U.) and 4dW (dif: 0.68 A.U.); and SDr was significantly greater in 5dW than in 3dW (dif: 0.77 A.U.) and 4dW (dif: 0.90 A.U.). Correlations between the weekly training loads and the match demands of the same week were small for PL (r = 0.250 [0.13;0.36]), ACC (r = 0.292 [0.17;0.40]) and DEC (r = 0.236 [0.11;0.35]). This study reveals that ratios of above 1 were observed for specific measures (e.g., HSR, SD). It was also observed that training sessions are not adjusted according to weekly variations in match demands.

#3 Variations of Internal and External Load Variables between Intermittent Small-Sided Soccer Game Training Regimens
Reference: Int J Environ Res Public Health. 2019 Aug 15;16(16). pii: E2923. doi: 10.3390/ijerph16162923.
Authors: Clemente FM, Nikolaidis PT, Rosemann T, Knechtle B
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Summary: The purpose of this study was twofold: (i) analyze the variations of internal and external load between intermittent regimens (6 × 3' and 3 × 6') during a small-sided game (SSG); and (ii) analyze the variations of internal and external load within-intermittent regimens (between sets). Ten male amateur soccer players (age: 21.7 ± 2.1 years) participated in this study. Almost certain large decreases in total distance (-8.6%, [-12.3; -4.8], Effect Size (ES): -1.51, [-2.20; -0.82]) and running distance (-34.0%, [47.0; -17.8], ES: -2.23, [-3.40; -1.05]) were observed when comparing the 3 × 6' and 6 × 3'. Very likely moderate and large decreases in total accelerations (-24.0%, [-35.1; -10.9]; ES: -1.11, [-1.75; -0.47]) and total of decelerations (-26.7%, [-38.8; -12.1]; ES:-1.49, [-2.36; -0.62]), respectively, were found when comparing the 3 × 6' and 6 × 3'. Very likely increases in rated of perceived exertion in the set 3 in comparison to the 1st during the 3 × 6' SSG (34.5%, [12.4; 61.0], ES: 1.35, [0.53; 2.16]) and the 6 × 3' (29.9%, [11.6; 51.2]; ES: 1.17, [0.49; 1.85]). Longer sets increase the perception of effort and contribute to a large decrease in total and running distances, and total of accelerations and decelerations. Meaningful decreases in time-motion demands occur between sets 2 and 3 while perceived effort increases.

#4 Physical Performance Measures Correlate with Head Impact Exposure in Youth Football
Reference: Med Sci Sports Exerc. 2019 Aug 28. doi: 10.1249/MSS.0000000000002144. [Epub ahead of print]
Authors: Kelley ME, Jones DA, Espeland MA, Rosenberg ML, Miles CM, Whitlow CT, Maldjian JA, Stitzel JD, Urban JE
Summary: Head impact exposure (HIE) (i.e., magnitude and frequency of impacts) can vary considerably among individuals within a single football team. To better understand individual-specific factors that may explain variation in head impact biomechanics, this study aimed to evaluate the relationship between physical performance measures and HIE metrics in youth football players. Head impact data were collected from youth football players using the Head Impact Telemetry (HIT) System. HIE was quantified in terms of impact frequency, linear and rotational head acceleration, and risk-weighted cumulative exposure metrics (RWELinear, RWERotational, and RWECP). Study participants completed 4 physical performance tests: vertical jump, shuttle run, 3-cone, and 40 yard sprint. The relationships between performance measures and HIE metrics were evaluated using linear regression analyses. A total of 51 youth football athletes (ages: 9-13 years old) completed performance testing and received a combined 13,770 head impacts measured with the HIT System for a full season. All performance measures were significantly correlated with total number of impacts in a season, RWELinear-Season, and all RWE-Game metrics. The strongest relationships were between 40 yard sprint speed and all RWE-Game metrics (all p≤0.0001 and partial R>0.3). The only significant relationships among HIE metrics in practice were between shuttle run speed and total practice impacts and RWELinear-Practices, 40 yard sprint speed and total number of practice impacts, and 3-cone speed and 95th percentile number of impacts/practice. Generally, higher vertical jump height and faster times in speed and agility drills were associated with higher HIE, especially in games. Physical performance explained less variation in HIE in practices, where drills and other factors, such as coaching style, may have a larger influence on HIE.

#5 Proprioception is not associated with lower extremity injuries in U21 high-level football players
Reference: Eur J Sport Sci. 2019 Aug 30:1-20. doi: 10.1080/17461391.2019.1662492. [Epub ahead of print]
Authors: Namazi P, Zarei M, Abbasi H, Hovanloo F, Rommers N, Rössler R
Summary: Football is a contact sport with a significant risk of injury. Although proprioception is well studied in rehabilitation, little is known about the association between proprioception and the occurrence of sport injuries. The purpose of this study was to look into the association between ankle and knee proprioception and lower extremity injuries in young football players. 73 football players from the highest U-21 league in Iran volunteered to participate in this study. Before the start of the 2017-2018 competitive season, joint position sense was measured at 30°, 60° and 90° knee flexion and at 10° and 15° ankle dorsiflexion, and inversion using the Biodex Isokinetic pro 4 system. The teams' medical staff recorded football-related lower extremity injuries. We used mixed effects Cox regression models to calculate hazard ratios (HRs) with 95% CIs, acknowledging the clustered data structure. 22 players (30.1%) suffered one or more lower extremity injuries during the season. None of the proprioception measures examined was significantly associated with the risk of lower extremity injuries. Based on these results of our sample, joint position sense does not seem to be associated with lower extremity injuries in young male football players.

#6 Few training sessions between return to play and first match appearance are associated with an increased propensity for injury: a prospective cohort study of male professional football players during 16 consecutive seasons
Reference: Br J Sports Med. 2019 Aug 29. pii: bjsports-2019-100655. doi: 10.1136/bjsports-2019-100655. [Epub ahead of print]
Authors: Bengtsson H, Ekstrand J, Waldén M, Hägglund M
Summary: It has been hypothesised that injury risk after return to play following an injury absence is influenced by the amount of training completed before return to competition. The aim was to analyse if the number of completed training sessions between return to play and the first subsequent match appearance was associated with the odds of injury in men's professional football. From a cohort study, including 303 637 individual matches, 4805 first match appearances after return to play following moderate to severe injuries (≥8 days absence) were analysed. Rate ratios (RRs) were used to compare injury rates in the first match appearances with the average seasonal match injury rate. Odds ratios (ORs) were used to analyse associations between the number of completed training sessions and general (all injuries), muscle, and non-muscle injury odds. Injury rate in the first match after return to play was increased by 87% compared with the average seasonal match injury rate (46.9 vs 25.0/1000 hours, RR=1.87; 95% CI 1.64 to 2.14). The odds of injury dropped 7% with each training session before the first match (OR 0.93; 95% CI 0.87 to 0.98). The same association was found for muscle injuries (OR 0.87; 95% CI 0.79 to 0.95) but not for non-muscle injuries (OR 0.99; 95% CI 0.91 to 1.07). Injury rates in the first match after injury are higher than the average seasonal match injury rate, but the propensity for player injury is decreased when players complete more training sessions before their first match.

#7 C-Reactive Protein Serum Levels as an Internal Load Indicator of Sprints in Competitive Football Matches
Reference: Int J Sports Med. 2019 Aug 29. doi: 10.1055/a-0985-4464. [Epub ahead of print]
Authors: Jatene P, Dos Santos GS, Portella DL
Summary: This study compared internal load variable dynamics across three consecutive football matches and investigated its relationship with the number of sprints performed by players. Twenty-three male players had blood and salivary samples collected for hormonal concentration (testosterone, cortisol, and testosterone-cortisol ratio), and serum analysis (interleukin-6, interleukin-1-beta, and c-reactive-protein), respectively. Sprints were measured through Global Position System devices. Testosterone and testosterone-cortisol-ratio presented a decreasing behavior up to the second match, and all other indicators presented an increasing behavior during the same period, c-reactive-protein was the only indicator observed to significantly rise up to the third match as well (0.38±0.02 mg/L; 0.49±0.05 mg/L; 0.69±0.05 mg/L; 0.89±0.08 mg/L). C-reactive-protein showed strong correlations with sprints in the second and third matches (p<0.01, r=0.71 and 0.79), and weak-to-moderate in the first one (p<0.05, r=0.59). Interleukin-6 and interleukin-1-beta presented weak-to-moderate correlation in every match (p<0.05, r=0.48 to 0.51; r=0.51 to 0.55) while testosterone-cortisol ratio presented weak-to-moderate correlation only in the third one (p<0.05, r=0.42). Multilevel linear regression showed that c-reactive-protein had a higher R2 than other biomarker in any regression model (R2=0.624; p<0.001). Therefore, c-reactive-protein can be a valid and reliable indicator of sprinting in competitive football. Future research should explore longer periods of monitoring and/or others external load variables so that other behaviors may arise to knowledge.

#8 Radiographic analysis of lower limb alignment in professional football players
Reference: Arch Orthop Trauma Surg. 2019 Aug 28. doi: 10.1007/s00402-019-03266-9. [Epub ahead of print]
Authors: Krajnc Z, Drobnič M
Summary: The purpose was to radiographically analyze lower limb alignment in adult asymptomatic professional football players and to correlate these values to clinical measurements. Twenty-four asymptomatic players [24.2 (3.6) years] were enrolled. Standard bilateral lower limb anteroposterior weight-bearing radiographs were acquired and clinical measurement of intercondylar/intermalleolar (ICD/IMD) distance was performed. Coronal plane mechanical alignment was assessed by five angles: leg mechanical axis (LMA), lateral proximal femoral angle (LPFA), lateral distal femoral angle (LDFA), medial proximal tibial angle (MPTA), and lateral distal tibial angle (LDTA). Their values were compared to the reference values for adult population. An inter-individual comparison between right/left and dominant/non-dominant leg was added. The sum of bilateral LMA was correlated against ICD/IMD and against ICD/IMD adjusted for body height. Football players presented with ICD/IMD of 46.5 (19.8) mm. Two, out of five, lower leg coronal angles showed significant differences (p < 0.001) compared to reference data from literature: LMA 5.8 (3.0)º vs.1.2 (2.2)º and MPTA 83.5 (2.6)º vs. 87.2 (1.5)º. No significant differences between left/right leg and dominant/non-dominant leg were established. Summed up bilateral LMA showed a high correlation to IMD/ICD (r = 0.8395; R2 = 0.7048), and even higher to ICD/IMD adjusted for body height (r = 0.8543; R2 = 0.7298). This study was radiographically confirming increased varus of elite football players toward general population. Apex of the varus deformity was located in the proximal tibia. Clinical measurement of ICD/IMD adjusted for body height highly correlated with the radiographic values of coronal alignment; therefore, it may be used in population studies.

#9 Short term effects of a weight loss and healthy lifestyle programme for overweight and obese men delivered by German football clubs
Reference: Eur J Sport Sci. 2019 Aug 28:1-35. doi: 10.1080/17461391.2019.1660809. [Epub ahead of print]
Authors: Pietsch B, Weisser B, Hanewinkel R, Gray C, Hunt K, Wyke S, Morgenstern M
Summary: Numbers of obese and overweight people continue to grow in Germany as they do worldwide. Men are affected more often but do less about it and few weight loss services attract men in particular. To evaluate the effectiveness of a men-only weight loss program, Football Fans in Training (FFIT), delivered by football clubs in the German Bundesliga, we did a non-randomized trial with a waiting list control group. Participants' data were collected between January 2017 and July 2018. FFIT is a 12-week, group-based, weight loss program and was delivered in stadia and facilities of 15 professional German Bundesliga clubs. Inclusion criteria were age 35-65 years, BMI ≥ 28 and waist circumference ≥100 cm. Clubs recruited participants through Social Media, E-Mail and match day advertisement. 477 German male football fans were allocated to the intervention group by order of registration date at their respective clubs. 84 participants on waiting list were allocated to the control group. Primary outcome was mean difference in weight loss with treatment condition over time as independent variable. We performed a multilevel mixed-effects linear regression analysis. Results were based on Intention-to-treat (ITT) analysis with Multiple Imputation. After 12 weeks, the mean weight loss of the intervention group adjusted for club, course and participants' age was 6.24 kg (95% CI 5.82 to 6.66) against 0.50 kg (-0.47 to 1.49) in the comparison group (p < 0.001). The results indicate that Football Fans in Training effectively helped German men to reduce their weight and waist circumference.

#10 Use of functional performance tests in sports: Evaluation proposal for football players in the rehabilitation phase
Reference: Turk J Phys Med Rehabil. 2018 May 15;64(2):148-154. doi: 10.5606/tftrd.2018.1462. eCollection 2018 Jun.
Authors: Gomez-Piqueras P, Gonzalez-Rubio J, Sainz de Baranda P, Najera A
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Summary: Based on the criteria of a group of experts, this study aims to select a set of functional performance tests which can be applied to evaluate the functional status of a football player in the recovery process and make a decision in relation to their return to practice. A total of 16 experts were selected by the coordinator group to judge an initial list of functional performance tests and, thus, reach a consensus about the tests which are best suited to the needs of the injured player. Each of the experts had to evaluate each one of the tests in a scale from 1 to 5 in relation to their suitability. Delphi method was used to reach consensus in the expert group. From the initial list of 25, the tests which obtained the best evaluation were: Counter movement jump (4.3±0.9), Single hop test (4.1±0.8), Triple hop test (4.1±0.9), Crossover hop test (4.1±0.7), Yo-Yo intermittent recovery (4.2±0.6), Barrow test (4.1±0.6), Shuttle run 8¥5 m (4.1±0.8). Star excursion balance test (4±0.7) and Y balance test (4.1±0.7). In the opinion of the experts selected here, these tests are the ones which best respond to the needs involved in a complex decision such as RTP.

#11 Injury Incidence, Prevalence and Severity in High-Level Male Youth Football: A Systematic Review
Reference: Sports Med. 2019 Aug 26. doi: 10.1007/s40279-019-01169-8. [Epub ahead of print]
Authors: Jones S, Almousa S, Gibb A, Allamby N, Mullen R, Andersen TE, Williams M
Summary: At a young age, high-level youth footballers enter structured practice where they engage in regular training and matches. The academy system is considered fundamental to a young footballer's tactical, technical and physical development. Yet, with regular training and matches, high-level youth footballers may be exposed to the risk of injury. This systematic review analyses and summarises published scientific information on high-level youth football injury characteristics and calculates the risk of them sustaining an injury over the course of a typical season. The search was performed using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Of the 1346 studies found, 23 fulfilled the inclusion criteria. Quality assurance scores for the selected research articles ranged between two and five out of eight. A high degree of heterogeneity between studies was observed. The probability of sustaining a time-loss injury during a high-level youth season ranged between < 1% and 96% for under 9- to under 16-year age groups and 50% and 91% for under 18- to under 21-year age groups. Pooled estimates for total (training and match) incidence per 1000 h was 5.8 for youth players aged under 9 to under 21 years, 7.9 for older players (under 17-under 21 years) and 3.7 for younger aged players (under 9-under 16 years). Training injury incidence rate ranged from 0.69 to 7.9 per 1000 h for all age groups in youth football. Match injury incidence rate for high-level youth players ranged from 0.4 to 80.0 per 1000 h. Close to one-fifth (18%) of all high-level youth football injuries were classified as severe and required > 28 days recovery time. Muscle strain injury accounted for 37% of all injuries reported in youth football. High probabilities (> 90%) of sustaining a time-loss injury over one typical high-level football season were found. High-level youth players lose large portions of the seasonal development to injury, with players seemingly suffering long absences from training and matches, consequently affecting health and well-being and possibly burdening club/parental finances and healthcare systems.





Latest research in football - week 35 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Influence of poor preparation and sleep deficit on injury incidence in amateur small field football of both gender
Reference: Arch Orthop Trauma Surg. 2019 Aug 17. doi: 10.1007/s00402-019-03261-0. [Epub ahead of print]
Authors: Krutsch V, Clement A, Heising T, Achenbach L, Zellner J, Gesslein M, Weber-Spickschen S, Krutsch W
Summary: Amateur small-field football tournaments are rather common worldwide. Adequate preparation is essential for injury prevention. The consequences of insufficient injury preparation at this level are still unclear. This study investigates the factors influencing injuries in this football population. In 2017, medical students participating in a national amateur football tournament were analysed in a prospective cohort study. Injury incidence, injury pattern and factors influencing injuries were investigated according to the statement on data collection and injury definition of Fuller et al. (Br J Sports Med 40:193-201, 2006). Preparation for the tournament was assessed for both sexes by means of hours of sleep, alcohol consumption, training level and warm-up performance. Of 694 amateur football players (423 men and 271 women) with a mean age of 23 years (SD 2.5), 321 (21.1%) injuries happened during the tournament. 60% of injuries affected the lower extremity. The most common types of traumatic injury were skin abrasions (40.0%) and muscle strains (23.3%). The injury incidence of male players during match exposure was 469 per 1000 h football and significantly higher than in female players 313 (p = 0.025). One potential reason for the higher injury rate of male players as measure for inadequate preparation was significantly higher alcohol consumption the evening before the tournament (p < 0.001) and the after-effects on match day (p < 0.001). Additionally, male players reported less and inadequate sleep the night before the tournament (p < 0.007) and a lower warm-up rate before the matches compared to female players (p < 0.001). Small-field tournaments in football have a high injury incidence. Male players have a higher injury incidence than female players and show additionally a lack of sleep and alcohol consumption the night before the tournament and poor warm-up performance on match day. Adequate preparation for a football tournament is the key factor for preventing injuries, also in recreational football.

#2 Tattoos among elite football players during the 2019 FIFA Women's World Cup France
Reference: J Eur Acad Dermatol Venereol. 2019 Aug 17. doi: 10.1111/jdv.15890. [Epub ahead of print]
Authors: Kluger N
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Summary: Thirty-four percent of the men players harbored visible tattoos, without notable impact on performance or discipline on the field during the 2018 FIFA World Cup (FWC), [1]. In a spirit of gender equality, we performed the same study among elite women footballers enrolled in the 2019 FWC France with the same methodology [1]. Players' visible tattoos (location, colours) were reviewed using the Getty Images website [2]. We collected players and teams' statistics using the official FIFA website.

#3 Distribution of External Load During Acquisition Training Sessions and Match Play of a Professional Soccer Team
Reference: J Strength Cond Res. 2019 Aug 29. doi: 10.1519/JSC.0000000000003363. [Epub ahead of print]
Authors: Castillo D, Raya-González J, Weston M, Yanci J
Summary: The aim of this study was to use global position systems to analyze the external loads of the 3 different acquisition training sessions (ATS) with competitive matches in professional soccer players over a 6-week period. Sixteen professional soccer players participated in the study, which analyzed the distribution of external load during the training microcycle of a professional soccer team. The 3 types of ATS undertaken by the players were as follows: ATS1 (strength), ATS2 (endurance), and ATS3 (speed). The total distance covered, the distance covered at above 14 km·h, the distance covered >21 km·h, the number of high accelerations (>3 m·s), and player load were recorded. The results showed that external loads were consistently higher during matches when compared with all training sessions (range of effect sizes: 1.06-3.38). Between training session comparisons revealed higher external loads during ATS1 and ATS2, when compared with ATS3 (range of effect sizes: 0.60-2.41). The only external load variable that differed between ATS1 and ATS2 was the distance covered >21 km·h, which was higher for ATS1. Our findings suggest that technical staff should consider the physical demands of weekly periodization to understand the training process regarding optimizing player physical performance.

#4 Relationship Among Biological Maturation, Physical Characteristics, and Motor Abilities in Youth Elite Soccer Players
Reference:  J Strength Cond Res. 2019 Aug 29. doi: 10.1519/JSC.0000000000003346. [Epub ahead of print]
Authors: Itoh R, Hirose N
Summary: Studies investigating skeletal maturity and motor abilities in youth Asian elite soccer players are lacking. We aimed to investigate the cross-sectional relationship among skeletal age (SA), physical characteristics, and motor abilities in youth elite soccer players. Skeletal age is commonly used to estimate the maturity status of youth athletes using a hand-wrist radiograph. We enrolled 49 youth elite male soccer players (12.7 ± 0.2 years). Height, body mass, body fat percentage, circumference (thigh/calf), flexibility, 10-m/50-m sprint, 10-m × 5 shuttle run, the crank test, 5-step bounding, Yo-Yo intermittent recovery test level 2, and cooper run were measured. Participants were divided into early (n = 14), average (n = 22), and late (n = 13) maturation groups according to their chronological age (CA) and SA based on the following criteria: SA-CA < -1 year, SA-CA = ±1 year, and SA-CA > +1 year, respectively. The difference in parameters among the groups was analyzed using one-way analysis of variance and Tukey's post hoc test. Statistical significance was set at p < 0.05. The early and average maturation groups were taller and heavier and had a larger circumference than the late maturation group (p < 0.05). Conversely, the early and average groups were significantly faster in 50-m sprint (p < 0.05) and scored higher in 5-step bounding (p < 0.05) than the late group. There was no difference in other parameters among the groups. In conclusion, the difference in biological maturity influences physical and physiological development, particularly height and muscular power, in youth elite soccer players.

#5 Competencies for rating perceived exertion in amateur soccer players with and without intellectual disabilities
Reference: J Appl Res Intellect Disabil. 2019 Aug 30. doi: 10.1111/jar.12668. [Epub ahead of print]
Authors: Schmitz G, Meis JM, Hafferkamp M, Schmitz S
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Summary: Perception of exertion is essential for self-regulation in sports. The ability to rate perceived exertion (RPE) is regarded as psychophysiological competence, although cognitive components of RPE are largely unknown. The present study tested the hypothesis that cognitive processing speed, perseveration and figural fluency correlate with RPE. The present study tested relationships between the performance in neuropsychological tests and the competence for RPE assessed during soccer training in 30 adults with and 22 adults without intellectual disabilities. Mean correlation coefficients for RPE and heart rate differed significantly between participants with intellectual disabilities (r = .41) and participants without intellectual disabilities (r = .71). The variance of RPE could be partially explained by neuropsychological performance measures reflecting cognitive processing speed and perseveration and by age. The results point to an impaired perception of exertion in people with intellectual disabilities, which can be partially explained by individual neuropsychological competencies.

#6 Sports Specialization Is Not Associated With Greater Odds of Previous Injury in Elite Male Youth Soccer Players
Reference: Clin J Sport Med. 2019 Sep;29(5):368-373. doi: 10.1097/JSM.0000000000000643.
Authors: Frome D, Rychlik K, Fokas J, Chiampas G, Jayanthi N, LaBella C
Summary: The purpose was to determine the relationship between sport specialization and previous injury in elite male youth soccer players. Male youth soccer players (N = 2123) participated in this study.  Sport specialization, weekly training volume, training ratio, and age were utilized as risk factors. Previous sports-related injury, injury type (traumatic vs overuse), injury severity, and injury location were main outcomes measures.  Of 2099 participants (average age 13.2 ± 1.8 years), 61.7% were specialized in soccer (played soccer >8 mo/yr and no other sports) and 38.3% were nonspecialized (played soccer >8 mo/yr and also played other organized sports). Specialized athletes were older than nonspecialized athletes (13.7 ± 1.9 vs 12.5 ± 1.4, P < 0.0001). Thirty-three percent (690/2099) of athletes reported at least one previous sports-related injury for a total of 765 traumatic injuries and 25 overuse injuries. Distribution of injury type was similar for specialized and nonspecialized athletes. Among athletes with overuse injuries, nonspecialized athletes were more likely to report upper-extremity and trunk overuse injuries than specialized athletes. After accounting for age and weekly training volume, specialized athletes had decreased odds of reporting any previous injury compared with nonspecialized athletes [odds ratio (OR), 0.78; 95% confidence interval (CI), 0.64-0.95], and similar odds of reporting a previous lower-extremity (LE) overuse injury as nonspecialized athletes (OR, 0.70; 95% CI, 0.56-1.1). However, specialized athletes missed more practices due to injury than nonspecialized players [median = 3, interquartile range (IQR) 2-4 vs median = 2, IQR 2-4, P = 0.0003]. In this national sample of elite, male youth soccer players, after accounting for age and weekly training volume, specialized athletes had decreased odds of reporting any previous injury and similar odds of reporting a previous LE overuse injury as nonspecialized athletes. These data suggest the need for further research to determine whether injury risk related to sports specialization depends on sex, chosen sport, and skill/competitive level.

#7 Comparative efficacy of active recovery and cold water immersion as post-match recovery interventions in elite youth soccer
Reference: J Sports Sci. 2019 Aug 28:1-9. doi: 10.1080/02640414.2019.1660448. [Epub ahead of print]
Authors: Pooley S, Spendiff O, Allen M, Moir HJ
Summary: The current study compared cold-water immersion (CWI) and active recovery (AR) to static stretching (SS) on muscle recovery post-competitive soccer matches in elite youth players (n = 15). In a controlled crossover design, participants played a total of nine competitive soccer games, comprising three 80 minute games for each intervention (SS, CWI and AR). Muscle oedema, creatine kinase (CK), countermovement jump performance (CMJA) and perceived muscle soreness (PMS) were assessed pre-, immediately post-, and 48 hours post-match and compared across time-intervals and between interventions. Following SS, all markers of muscle damage remained significantly elevated (P < 0.05) compared to baseline at 48 hours post-match. Following AR and CWI, CMJA returned to baseline at 48 hours post-match, whilst CK returned to baseline following CWI at 48 hours post-match only. Analysis between recovery interventions revealed a significant improvement in PMS (P < 0.05) at 48 hours post-match when comparing AR and CWI to SS, with no significant differences between AR and CWI observed (P > 0.05). Analysis of %change for CK and CMJA revealed significant improvements for AR and CWI compared to SS. The present study indicated both AR and CWI are beneficial recovery interventions for elite young soccer players following competitive soccer matches, of which were superior to SS.

#8 Does soccer play lower blood pressure?
Reference: Dtsch Med Wochenschr. 2019 Aug;144(17):1229-1232. doi: 10.1055/a-0953-6509. Epub 2019 Aug 27. [Article in German]
Summary: Playing football leads to a sustainable improvement of cardiovascular risk factors, especially to a reduction of blood pressure in hypertension. For certain target groups football is more attractive with its team character than individual sports. However, the existing studies are not sufficient for an evidence-based recommendation. Therefore, no medical society explicitly recommends football for lowering blood pressure. Urgent studies are needed to adequately evaluate the value of football as a health sport. This includes a special training program and rules, the involvement of football clubs in these programs, the training of appropriate coaches and the involvement of interested physicians. Football could, with its popularity, motivate more people to exercise and contribute to a sustained reduction in cardiovascular disease.

#9 Seasonal Accumulated Workloads in Collegiate Men's Soccer: A Comparison of Starters and Reserves
Reference: J Strength Cond Res. 2019 Aug 23. doi: 10.1519/JSC.0000000000003257. [Epub ahead of print]
Authors: Curtis RM, Huggins RA, Benjamin CL, Sekiguchi Y, M Arent S, C Armwald B, Pullara JM, West CA, Casa DJ
Summary: The purpose of this investigation was to quantify and compare player's season total-, match-, and training-accumulated workload by player status characteristics (i.e., starter vs. reserve) in American collegiate men's soccer. Global positioning system (GPS) and heart rate (HR)-derived workloads were analyzed from 82 collegiate male soccer athletes from 5 separate teams over the 2016 and 2017 seasons. Differences in total physical and physiological workloads (i.e., total distance, accelerations, and weighted HR-zone training impulse [TRIMP] score) as well as workloads over a range of intensity zones were examined using multilevel mixed models, with mean difference (MD) and effect size (ES) reported. Starters accumulated substantially more total distance (MD = 82 km, ES = 1.23), TRIMP (MD = 2,210 au, ES = 0.63), and total accelerations (MD = 6,324 n, ES = 0.66) over the season. Total accumulated distance in all velocity zones (ES [range] = 0.87-1.08), all accelerations zones (ES [range] = 0.54-0.74), and time spent at 70-90% HRmax (ES [range] = 0.60-1.12) was also greater for starters. Reserves accumulated substantially more total distance (MD = 20 km, ES = 0.43) and TRIMP (MD = 1,683 au, ES = 0.79) during training. Although reserves show elevated physical and physiological loads during training compared with starters, there is an imbalance in overall workloads between player roles, with starters incurring substantially more match and total seasonal workloads. These results indicate managing player workloads in soccer requires attention to potential imbalances between players receiving variable match times. Coaches and practitioners in collegiate men's soccer may consider implementing strategies to reduce discrepancies in loading between starters and reserves. Individualized monitoring of training and match workloads may assist in the implementation of more balanced load management programs.

#10 Contextual Variables and Training Load Throughout a Competitive Period in a Top-Level Male Soccer Team
Reference: J Strength Cond Res. 2019 Aug 23. doi: 10.1519/JSC.0000000000003258. [Epub ahead of print]
Authors: Rago V, Rebelo A, Krustrup P, Mohr M
Summary: The aim of the present study was to investigate and quantify the weekly training load (TL) according to different match-related contextual factors in a professional male soccer team (n = 23). Training load was quantified using a 10-Hz global positioning system with integrated 100-Hz accelerometer and heart rate recordings over a 3-month competitive period. Total distance (TD) covered and high-speed running (HSR, >16 km·h) during training were higher in the week after playing against a bottom-level or top-level opponent compared to a medium-level opponent (p < 0.05; effect size [ES] = 0.30-1.04). TD was also higher when preparing for a match against a bottom-level opponent (p < 0.05; ES = 0.39-0.76). In addition, the percentage of HSR was higher after playing a bottom-level compared to a medium-level opponent (p < 0.001; ES = 0.49 [0.27; 0.71]). TD covered was higher in the week following a draw or a win, and higher before a loss compared to a draw (p < 0.05, ES = 0.32-0.81). Both absolute HSR and HSR expressed as percentage of TD were higher before losing and winning a match compared to a draw (p < 0.05; ES = 0.72-0.98). Weekly TL seems to be slightly affected by match-related contextual variables, with special emphasis on the opponent standard and match outcome. Higher training volume was observed before and after playing against a top-level opponent, and after losing a match, whereas the volume of high-intensity training seems to be higher when preparing for a game against a top-level opponent. Future experimental research should clarify the interaction between match-related contextual variables (e.g., cause) and weekly TL (e.g., effect).

#11 Relative Age Effect in Collegiate Soccer: Influence of Nationality, Playing Position, and Class
Reference: J Strength Cond Res. 2019 Aug 23. doi: 10.1519/JSC.0000000000003356. [Epub ahead of print]
Authors: Hurley E, Comstock BA, Haile L, Beyer KS
Summary: The purpose of this study was to evaluate the existence of relative age effects (RAEs) in collegiate soccer. In addition, the impact of nationality, position, class, and National Collegiate Athletic Association (NCAA) tournament qualification status on the prevalence of RAEs was assessed. Birth dates from male NCAA Division I soccer athletes (n = 4,082) from the 2017/2018 season were categorized into quarters based on calendar and scholastic quarters. All athlete birth-date distributions were compared with the expected birth-date distributions for the United States. International-born athletes (INT) displayed a significant difference in birth-date distribution when assessed with calendar quarters, whereas American-born athletes (USA) showed a significant difference in birth-date distributions when assessed with scholastic quarters. Furthermore, INT showed significant RAEs for midfielders and defenders, whereas USA showed significant RAEs midfielders and goalkeepers. In terms of class, INT had significant RAEs for all classes, whereas USA had significant RAEs only for freshmen and sophomores. All INT had significant RAEs regardless of tournament qualification status; however, USA had significant RAEs only for nontournament teams. In summary, significant RAEs exist in male Division I college soccer; however, the presence of RAEs is influenced by nationality, position, class, and NCAA tournament qualification status. Coaches should be aware of RAEs during the recruitment process to avoid potential selection bias.

#12 High-intensity endurance capacity assessment as a tool for talent identification in elite youth female soccer
Reference: J Sports Sci. 2019 Aug 26:1-7. doi: 10.1080/02640414.2019.1656323. [Epub ahead of print]
Authors: Datson N, Weston M, Drust B, Gregson W, Lolli L
Summary: Talent identification and development programmes have received broad attention in the last decades, yet evidence regarding the predictive utility of physical performance in female soccer players is limited. Using a retrospective design, we appraised the predictive value of performance-related measures in a sample of 228 youth female soccer players previously involved in residential Elite Performance Camps (age range: 12.7-15.3 years). With 10-m sprinting, 30-m sprinting, counter-movement jump height, and Yo-Yo Intermittent Recovery Test Level 1 (IR1) distance as primary predictor variables, the Akaike Information Criterion (AIC) assessed the relative quality of four penalised logistic regression models for determining future competitive international squads U17-U20 level selection. The model including Yo-Yo IR1 was the best for predicting career outcome. Predicted probabilities of future selection to the international squad increased with higher Yo-Yo IR1 distances, from 4.5% (95% confidence interval, 0.8 to 8.2%) for a distance lower than 440 m to 64.7% (95% confidence interval, 47.3 to 82.1%) for a score of 2040 m. The present study highlights the predictive utility of high-intensity endurance capacity for informing career progression in elite youth female soccer and provides reference values for staff involved in the talent development of elite youth female soccer players.





Latest research in football - week 34 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Eccentric-concentric Ratio: A Key Factor for Defining Strength Training in Soccer
Reference: Int J Sports Med. 2019 Aug 21. doi: 10.1055/a-0977-5478. [Epub ahead of print]
Authors: Nuñez FJ, Hoyo M, López AM, Sañudo B, Otero-Esquina C, Sanchez H, Gonzalo-Skok O
Summary: The aims of this study were to analyse the effect of chronic strength training over concentric power (CON), eccentric power (ECC), ECC/CON ratio, and 20 m linear sprint performance in elite young soccer players. Twenty young elite Spanish soccer players were assigned to an experimental group (CPG) which performed a front-step exercise using a conical pulley, 2-3 sets of 6 repetitions each leg, during 9 weeks (CPG, n=10) in addition to its usual strength training, or to a control group (CG, n=10). The improvements in the ECC mean power (36%, ES=1.61), and ECC / CON ratio (17%, ES=1.77) were substantially greater in the CPG than in the CG while the CON mean power (16%, ES=0.83) was substantially greater in the CG than in the CPG. The sprinting time for 10 m (2.8%, ES=0.78) and the 10 m flying time between 10-20 m (1.72%, ES=0.41) were substantially enhanced in CPG and CG respectively. To be efficient when defining a functional strength training and performance increments using an inertial device, the mean power output need to be measured during the CON and ECC phases and an analysis of the ECC / CON ratio should be included.

#2 Progressive strength training restores quadriceps and hamstring muscle strength within 7 months after ACL reconstruction in amateur male soccer players
Reference: Phys Ther Sport. 2019 Aug 9;40:10-18. doi: 10.1016/j.ptsp.2019.08.004. [Epub ahead of print]
Authors: Welling W, Benjaminse A, Lemmink K, Dingenen B, Gokeler A
Summary: The purpose of the current study was to compare the results of a progressive strength training protocol for soccer players after anterior cruciate ligament reconstruction (ACLR) with healthy controls, and to investigate the effects of the strength training protocol on peak quadriceps and hamstring muscle strength. Thirty-eight amateur male soccer players after ACLR were included. Thirty age-matched amateur male soccer players served as control group. Quadriceps and hamstring muscle strength was measured at three time points during the rehabilitation. Limb symmetry index (LSI) > 90% was used as cut-off criteria. Soccer players after ACLR had no significant differences in peak quadriceps and hamstring muscle strength in the injured leg at 7 months after ACLR compared to the dominant leg of the control group. Furthermore, 65.8% of soccer players after ACLR passed LSI >90% at 10 months for quadriceps muscle strength. Amateur male soccer players after ACLR can achieve similar quadriceps and hamstring muscle strength at 7 months compared to healthy controls. These findings highlight the potential of progressive strength training in rehabilitation after ACLR that may mitigate commonly reported strength deficits.

#3 Analysis of Playing Area Dimensions in Spanish Professional Soccer: Extrapolation to the Design of Small-Sided Games With Tactical Applications
Reference: J Strength Cond Res. 2019 Aug 15. doi: 10.1519/JSC.0000000000003226. [Epub ahead of print]
Authors: Caro O, Zubillaga A, Fradua L, Fernandez-Navarro J
Summary: The aims of this study were to examine (a) the width and length dimensions of the playing area in 4v4 situations during competition, (b) the influence of the pitch zone where the ball is on 4v4 dimensions, and (c) the influence of match status on the dimensions of 4v4 situations. Data were collected from 25 matches from the Spanish La Liga of the 2007-2008 season using the Amisco system. Length, width, and individual playing area (IPA) of the rectangle that included the nearest 4 players to the ball from each team were collected in a total of 8,727 4v4 game situations. The pitch zone and match status were also considered for these 4v4 situations. To determine factors that affect 4v4 game situations, 1-way analysis of variance was used. The influence of the pitch zone where 4v4 situations took place showed significant differences (p < 0.001) between the zones where different principles of the game apply. The areas of the 4v4 situations ranged from 14.70 ± 4.69 × 17.18 ± 6 to 17.09 ± 5.16 × 20.34 ± 5.93 m, and the IPA of the 4v4 playing rectangle ranged from 46.33 ± 20 to 35.48 ± 16.95 m, being larger in the central zones of the pitch. The length of the 4v4 rectangle showed a significant reduction in the closer zones to the goal. Match status did not affect the dimensions of these 4v4 game situations significantly. The findings of this study suggest that the size of 4v4 situations proposed for training should be designed according to the pitch zone where playing actions take place.

#4 Augmented-Feedback Training Improves Cognitive Motor Performance of Soccer Players
Reference: Med Sci Sports Exerc. 2019 Aug 16. doi: 10.1249/MSS.0000000000002118. [Epub ahead of print]
Authors: Hicheur H, Chauvin A, Cavin V, Fuchslocher J, Tschopp M, Taube W
Summary: In this study, we tested the hypothesis that augmented feedback (AF) training can improve both perceptual-cognitive and/or motor skills specific to soccer. Three groups of young elite players (U14-U15 categories) performed a test consisting in passing the ball as accurately and as quickly as possible towards a visual target moving briefly across a large screen located at 6 meters from the player. The performed task required players to correctly perceive the target, anticipate its future location and to adequately adjust the pass direction and power. The control group (CON) performed normal soccer training and was compared with two visuomotor training groups (AF and No-Feedback NF) that followed the same training regime but integrated series of 32 passes three times per week over a seventeen-day period into their normal soccer training. Objective measurements of the passing performance were provided using a high-technology system (COGNIFOOT) prior to, during and after training. During training, only players of the AF-group received visuo-auditory feedback immediately after each trial informing them about the accuracy of their passes. The results show that only players of the AF-group significantly improved passing accuracy, reactiveness, and global passing performance (+22 %) whereas the NF-group only improved passing accuracy. None of these parameters was improved in the CON-group. The objectively measured changes in passing performance were compared to the more subjectively judged passing performance provided by coaches and players. Coaches' judgments were more reliable than players' judgments and exhibited a training group effect comparable to the ones objectively measured by COGNIFOOT. This study provides evidence that the training of cognitive motor performance in soccer players highly benefits from the use of augmented feedback.

#5 Effects of mental fatigue on passing decision-making performance in professional soccer athletes
Reference: Eur J Sport Sci. 2019 Aug 19:1-21. doi: 10.1080/17461391.2019.1656781. [Epub ahead of print]
Authors: Gantois P, Caputo Ferreira ME, Lima-Junior D, Nakamura FY, Batista GR, Fonseca FS, de Sousa Fortes L
Summary: The aim of this study was to analyze the effect of mental fatigue on passing decision-making in professional soccer athletes. A controlled and counterbalanced cross-over design was adopted consisting of three visits with a 1-week interval between sessions. Twenty (20) professional soccer male athletes participated in three randomized conditions divided into three visits: control, 15-min Stroop task, and 30-min Stroop task. Inhibitory control was accessed by the Stroop task (accuracy and response time) before and after induced mental fatigue protocol. The athletes played a training match (90-min) following the experimental conditions. The Game Performance Assessment Instrument (GPAI) was used for the passing decision-making analysis. The GPAI analysis showed impaired passing decision-making performance following the 30-min Stroop task compared with the 15-min and control condition (F(2,17) = 6.99, p = .01). Moreover, an increase in response time during the Stroop task was found following 30-min Stroop task condition (F(2,17) = 6.57, p = .03) compared to 15-min of Stroop task and control conditions. Prolonged cognitive tasks may be considered a mediating factor in passing decision-making performance in male professional soccer athletes throughout a full-length training match. Thus, athletes should avoid highly demanding-cognitive tasks before a soccer match. Future studies are required to explore more ecological cognitive tasks to induce mental fatigue (i.e. smartphones and video-games) and their effects on other performance indicators (e.g., physical, technical, tactical) in a full-length training match setting.

#6 Using differential ratings of perceived exertion to assess agreement between coach and player perceptions of soccer training intensity: An exploratory investigation
Reference: J Sports Sci. 2019 Aug 19:1-6. doi: 10.1080/02640414.2019.1653423. [Epub ahead of print]
Authors: Macpherson TW, McLaren SJ, Gregson W, Lolli L, Drust B, Weston M
Summary: We aimed to assess the coach-player agreement of subjective soccer training loads via differential ratings of perceived exertion (dRPE). The coach initially underwent quantifiable familiarisation (blackness test) with the Borg CR100 scale. Data were collected from 16 semi-professional soccer players across seven consecutive training sessions. For the measurement of subjective training load, the coach and players provided dRPE (CR100) for legs (RPE-L), breathlessness (RPE-B) and technical exertion (RPE-T). Coach-prescribed dRPE were recorded prior to training, with coach observed and player reported dRPE collected post training. Statistical equivalence bounds for agreement between coach (prescribed and observed) and player reported dRPE scores were 4 arbitrary units on the CR100 and we used a probability outcome of likely (≥75%) to infer realistic equivalence. Following three familiarisation sessions, the coach improved their blackness test score from 39% to 83%. Coach observed and player reported RPE-T scores were likely equivalent, with all other comparisons not realistically equivalent. Since training prescription is coach-led, our data highlight the importance of accurate internal load measurement and feedback in soccer. The improved accuracy and precision of coach intensity estimation after three attempts at the blackness test suggests that this method could be worthwhile to researchers and practitioners employing dRPE.

#7 The effects of detraining and retraining periods on fat-mass and fat-free mass in elite male soccer players
Reference: PeerJ. 2019 Aug 13;7:e7466. doi: 10.7717/peerj.7466. eCollection 2019.
Authors: Suarez-Arrones L, Lara-Lopez P, Maldonado R, Torreno N, De Hoyo M, Nakamura FY, Di Salvo V, Mendez-Villanueva A
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Summary: The aim of the study was to examine the effects of a detraining period (DTP) (i.e., off-season) with an individually prescribed training program, and a retraining period (RTP) (i.e., pre-season) combining soccer and flywheel-based strength training on fat-free mass (FFM) and fat-mass (FM) in 10 elite professional male soccer players. The present study used a controlled repeated-measures research design to investigate the changes in FFM and FM using dual-energy X-ray absorptiometry. Whole body %FM increased (effect size (ES) = 0.87 ± 0.46) and FFM reduced after DTP (ES = -0.30 ± 0.19), returning to values comparable to the end of the previous season after RTP. At regional levels, arms, legs, and trunk %FM increased (ES = from 0.42 to 1.29) while trunk-FFM was reduced (ES = -0.40 ± 0.26) after DTP, returning to the values observed at the end of the previous season after RTP. Legs-FFM did not change after DTP, with a substantial increase after RTP in comparison with pre-season values (ES = 0.34 ± 0.29 and 0.53 ± 0.36 for the right and left leg, respectively). Despite the small sample size of the present study, the findings indicate that elite soccer players can be allowed 2 weeks of rest during a five-week DTP, since the changes in %FM and FFM were relatively small, and FM and FFM returned to the optimal initial values for competition after the proposed RTP during the pre-season.

#8 The Effects of a Single Versus Three Consecutive Sessions of Football Training on Postprandial Lipemia: a Randomized, Controlled Trial in Healthy, Recreationally Active Males
Reference: Sports Med Open. 2019 Aug 22;5(1):38. doi: 10.1186/s40798-019-0212-1.
Authors: Paul DJ, Bangsbo J, Cherif A, Nassis GP
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Summary: Exercise frequency is important for maintaining health; however, its effects on postprandial responses remain largely unknown. Better understanding this during popular sports activities such as football may influence exercise habits. Therefore, the aim of the present study was to examine the effects of playing one single versus three consecutive days of 60-min small-sided football matches on postprandial lipemia. Fifteen males performed either one (1FOOT; n = 7) or three 60-min football (3FOOT; n = 8) sessions across an 8-day trial period. On day 1, a blood sample was collected at fasted (0 min) and 0.75, 2, 4, 6 h after a high-fat meal. Participants were then randomly allocated to the 1FOOT (day 7) or 3FOOT (days 5, 6, 7) condition. On day 8, they repeated the high-fat meal and blood sampling for 6 h following the meal. Postprandial total and incremental area under the curve (AUC, iAUC, respectively) were calculated. The postprandial triglyceride iAUC was 41% lower from pre- to post-measures for the 1FOOT (p < 0.05; ES = 1.02) and 15.7% lower for the 3FOOT (ns; ES = 0.41). Total triglyceride AUC was lower (26%) post-football matches in the 3FOOT group only (p < 0.01; ES = 1.23). In 3FOOT, insulin concentration was lower for post- compared to pre-measures at 0.75 and 2 h, respectively (p < 0.001). One single 60-min small-sided football match lowered postprandial TG incremental area under the curve while performing three consecutive days of football matches did not result in a greater attenuation.

#9 The Dependence of Running Speed and Muscle Strength on the Serum Concentration of Vitamin D in Young Male Professional Football Players Residing in the Russian Federation
Reference: Nutrients. 2019 Aug 21;11(9). pii: E1960. doi: 10.3390/nu11091960.
Authors: Bezuglov E, Tikhonova A, Zueva A, Khaitin V, Lyubushkina A, Achkasov E, Waśkiewicz Z, Gerasimuk D, Żebrowska A, Nikolaidis PT, Rosemann T, Knechtle B
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Summary: Vitamin D insufficiency is prevalent among athletes, and it can negatively affect physical performance. At the same time, most of the available data were obtained from untrained individuals of various ages, and published studies performed in athletes led to contradictory conclusions. This cohort prospective study examined the serum concentration of 25-hydroxycalciferol (25(OH)D) and its association with running speed and muscle power in 131 young football players (mean age 15.6 ± 2.4 years). 25(OH)D levels were below reference in 42.8% (serum 25(OH)D <30 ng/mL) and above reference in 30.5% of the participants (serum 25(OH)D 61-130 ng/mL). A comparison of the results of 5, 15, and 30 m sprint tests and the standing long jump test found no statistically significant differences between the two groups. Athletes from the 25(OH)D-insufficient group were treated with 5000 IU cholecalciferol supplement daily for 60 days. After the treatment, the 25(OH)D concentration increased by 79.2% and was within reference in 84% of the treated athletes (serum 25(OH)D 30-60 ng/mL). Testing was repeated after the end of treatment, and a statistically significant increase in the results of the 5, 15, and 30 m sprint tests was observed (Cohen's d was 0.46, 0.33, and 0.34, respectively), while the results of the standing long jump test remained unchanged. Body height, body weight, and lean body mass of the football players also increased. These findings indicate that there is likely no correlation between serum levels of 25(OH)D, muscle power, and running speed in young professional football players, and the changes observed post-treatment might have been caused by changes in the anthropometric parameters. During the study, all the anthropometric parameters changed, but the amount of lean body mass only correlated with the results of the 5 m sprint.

#10 Extracting spatial-temporal features that describe a team match demands when considering the effects of the quality of opposition in elite football
Reference: PLoS One. 2019 Aug 22;14(8):e0221368. doi: 10.1371/journal.pone.0221368. eCollection 2019.
Authors: Gonçalves B, Coutinho D, Exel J, Travassos B, Lago C, Sampaio J
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Summary: Spatiotemporal patterns of play can be extracted from competitive environments to design representative training tasks and underlying processes that sustain performance outcomes. To support this statement, the aims of this study were: (i) describe the collective behavioural patterns that relies upon the use of player positioning in interaction with teammates, opponents and ball positioning; (ii) and define the underlying structure among the variables through application of a factorial analysis. The sample comprised a total of 1,413 ball possession sequences, obtained from twelve elite football matches from one team (the team ended the season in the top-5 position). The dynamic position of the players (from both competing teams), as well as the ball, were captured and transformed to two-dimensional coordinates. Data included the ball possession sequences from six matches played against top opponents (TOP, the three teams classified in the first 3 places at the end of the season) and six matches against bottom opponents (BOTTOM, the three teams classified in the last 3 at the end of the season). The variables calculated for each ball possession were the following: ball position; team space in possession; game space (comprising the outfield players of both teams); position and space at the end of ball possession. Statistical comparisons were carried with magnitude-based decisions and null-hypothesis analysis and factor analysis to define the underlying structure among variables according to the considered contexts. Results showed that playing against TOP opponents, there was ~38 meters game length per ~43 meters game width with 12% of coefficient of variation (%). Ball possessions lasted for ~28 seconds and tended to end at ~83m of pitch length. Against BOTTOM opponents, a decrease in the game length with an increase in game width and in the deepest location was observed in comparison with playing against TOP opponents. The duration of ball possession increased considerable (~37 seconds), and the ball speed entropy was higher, suggesting lower levels of regularity in comparison with TOP opponents. The BOTTOM teams revealed a small EPS. The Principal Component Analysis showed a strong association of the ball speed, entropy of the ball speed and the coefficient of variation (%) of the ball speed. The EPS of the team in possession was well correlated with the game space, especially the game width facing TOP opponents. Against BOTTOM opponents, there was a strong association of ball possession duration, game width, distance covered by the ball, and length/width ratio of the ball movement. The overall approach carried out in this study may serve as the starting point to elaborate normative models of positioning behaviours measures to support the coaches' operating decisions.

#11 Physical and Tactical Demands of the Goalkeeper in Football in Different Small-Sided Games
Reference: Sensors (Basel). 2019 Aug 19;19(16). pii: E3605. doi: 10.3390/s19163605.
Authors: Jara D, Ortega E, Gómez-Ruano MÁ, Weigelt M, Nikolic B, Sainz de Baranda P
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Summary: Several studies have examined the differences between the different small-sided game (SSG) formats. However, only one study has analysed how the different variables that define SSGs can modify the goalkeeper's behavior. The aim of the present study was to analyze how the modification of the pitch size in SSGs affects the physical demands of the goalkeepers. Three professional male football goalkeepers participated in this study. Three different SSG were analysed (62 m × 44 m for a large pitch; 50 m × 35 m for a medium pitch and 32 m × 23 m for a small pitch). Positional data of each goalkeeper was gathered using an 18.18 Hz global positioning system. The data gathered was used to compute players' spatial exploration index, standard ellipse area, prediction ellipse area The distance covered, distance covered in different intensities and accelerations/decelerations were used to assess the players' physical performance. There were differences between small and large SSGs in relation to the distances covered at different intensities and pitch exploration. Intensities were lower when the pitch size was larger. Besides that, the pitch exploration variables increased along with the increment of the pitch size.





Latest research in football - week 33 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Validity and reliability of speed tests used in soccer: A systematic review
Reference: PLoS One. 2019 Aug 14;14(8):e0220982. doi: 10.1371/journal.pone.0220982. eCollection 2019.
Authors: Altmann S, Ringhof S, Neumann R, Woll A, Rumpf MC
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Summary: Speed is an important prerequisite in soccer. Therefore, a large number of tests have been developed aiming to investigate several speed skills relevant to soccer. This systematic review aimed to examine the validity and reliability of speed tests used in adult soccer players. A systematic search was performed according to the PRISMA guidelines. Studies were included if they investigated speed tests in adult soccer players and reported validity (construct and criterion) or reliability (intraday and interday) data. The tests were categorized into linear-sprint, repeated-sprint, change-of-direction sprint, agility, and tests incorporating combinations of these skills. In total, 90 studies covering 167 tests were included. Linear-sprint (n = 67) and change-of-direction sprint (n = 60) were studied most often, followed by combinations of the aforementioned (n = 21) and repeated-sprint tests (n = 15). Agility tests were examined fewest (n = 4). Mainly based on construct validity studies, acceptable validity was reported for the majority of the tests in all categories, except for agility tests, where no validity study was identified. Regarding intraday and interday reliability, ICCs>0.75 and CVs<3.0% were evident for most of the tests in all categories. These results applied for total and average times. In contrast, measures representing fatigue such as percent decrement scores indicated inconsistent validity findings. Regarding reliability, ICCs were 0.11-0.49 and CVs were 16.8-51.0%. Except for agility tests, several tests for all categories with acceptable levels of validity and high levels of reliability for adult soccer players are available. Caution should be given when interpreting fatigue measures, e.g., percent decrement scores. Given the lack of accepted gold-standard tests for each category, researchers and practitioners may base their test selection on the broad database provided in this systematic review. Future research should pay attention to the criterion validity examining the relationship between test results and match parameters as well as to the development and evaluation of soccer-specific agility tests.

#2 Correlation of Fiber-Type Composition and Sprint Performance in Youth Soccer Players
Reference: J Strength Cond Res. 2019 Aug 8. doi: 10.1519/JSC.0000000000003320. [Epub ahead of print]
Authors: Metaxas T, Mandroukas A, Michailidis Y, Koutlianos N, Christoulas K, Ekblom B
Summary: The aim of this study was to examine the correlation between muscle fiber type and sprint performance in elite young soccer players of different age groups of the same team. Twenty-eight young players participated in this study (group U15, n = 8; group U13, n = 9; and group U11, n = 11). Anthropometric assessments, acceleration (10 m), and Bangsbo modified sprint test (30 m) were performed. Muscle biopsies were obtained from the vastus lateralis, and after that, fiber-type composition was determined by immunohistochemistry. No significant correlations were found between the sprint test and muscle fiber distribution for the groups U13 and U11 (p > 0.05). Also, no correlations were found between cross-sectional areas in the types of fibers with the sprint test in all groups (p > 0.05). A positive correlation was found between type I fibers and the performance in the acceleration test (10 m) (r = 0.77, p < 0.05) was found only in group U15 and a negative correlation between type IIA fibers and the performance in the acceleration test (10 m) (r = -0.89, p < 0.05). The correlations were observed only in group U15, which may indicate that the duration and the intensity of the soccer systematic training can affect the plasticity of the muscle fibers. Specific soccer training in youth is one of the factors that can affect fiber-type plasticity. The specific training programs and status of U15 are more intensive, and the exercises are oriented more to improve physical fitness.

#3 Biomarker Response to a Competitive Season in Division I Female Soccer Players
Reference: J Strength Cond Res. 2019 Aug 8. doi: 10.1519/JSC.0000000000003264. [Epub ahead of print]
Authors: Walker AJ, McFadden BA, Sanders DJ, Rabideau MM, Hofacker ML, Arent SM
Summary: The purpose of this study was to evaluate effects of training load (TL) on performance and biomarkers of health, performance, and recovery in Division I female soccer players throughout a competitive season. Participants (N = 25, Mage = 20 ± 1.1 years) were monitored before the start of preseason and every 4-weeks thereafter (T1-T5). A battery of performance tests was administered before the start of preseason (P1) and end-of-season (P2), including body composition (percent body fat [%BF], fat free mass [FFM], and fat mass), vertical jump (VJ), and V[Combining Dot Above]O2max. Blood draws were conducted at every time point (T1-T5) to assess free and total cortisol (CORTF and CORTT), prolactin (PRL), T3, IL-6, creatine kinase (CK), sex-hormone binding globulin, omega-3 (n-3FA), vitamin-D (Vit-D), iron (Fe), hematocrit (HcT), ferritin (Fer), percent saturation (%Sat), and total iron-binding capacity (TIBC). Daily exercise energy expenditure (EEE) and TL were determined. There were significant declines in V[Combining Dot Above]O2max, VJ, weight, and %BF from P1-P2 (p < 0.05) with no significant differences in FFM. Training load and EEE significantly decreased from T1-T3 (p < 0.05). Significant increases were seen in CORTT, CORTF, PRL, T3, IL-6, CK, and TIBC throughout the season (p < 0.05). Significant decreases were seen in n-3FA, Fe, Fer, %Sat, and Hct throughout the season (p < 0.05). Female athletes experience significant physiological changes following high TL and EEE associated with preseason and appear to be further exacerbated by the cumulative effects of the season. Unique insights provided by biomarkers enable athletes and coaches to be cognizant of the physiological changes that are occurring throughout the season.

#4 Where to go: Computational and visual what-if analyses in soccer
Reference: J Sports Sci. 2019 Aug 11:1-9. doi: 10.1080/02640414.2019.1652541. [Epub ahead of print]
Authors: Stein M, Seebacher D, Marcelino R, Schreck T, Grossniklaus M, Keim DA, Janetzko H
Summary: To prepare their teams for upcoming matches, analysts in professional soccer watch and manually annotate up to three matches a day. When annotating matches, domain experts try to identify and improve suboptimal movements based on intuition and professional experience. The high amount of matches needing to be analysed manually result in a tedious and time-consuming process, and results may be subjective. We propose an automatic approach for the realisation of effective region-based what-if analyses in soccer. Our system covers the automatic detection of region-based faulty movement behaviour, as well as the automatic suggestion of possible improved alternative movements. As we show, our approach effectively supports analysts and coaches investigating matches by speeding up previously time-consuming work. We enable domain experts to include their domain knowledge in the analysis process by allowing to interactively adjust suggested improved movement, as well as its implications on region control. We demonstrate the usefulness of our proposed approach via an expert study with three invited domain experts, one being head coach from the first Austrian soccer league. As our results show that experts most often agree with the suggested player movement (83%), our proposed approach enhances the analytical capabilities in soccer and supports a more efficient analysis.

#4 Relative Age Effect in the Sport Environment. Role of Physical Fitness and Cognitive Function in Youth Soccer Players
Reference: Int J Environ Res Public Health. 2019 Aug 8;16(16). pii: E2837. doi: 10.3390/ijerph16162837.
Authors: Huertas F, Ballester R, Gines HJ, Hamidi AK, Moratal C, Lupiáñez J
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Summary: The need to achieve short-term competitive outcomes in sports may influence the emergence of talent selection strategies, which could bias individuals' opportunities. The present study aimed to further explore the relative age effect (RAE), a phenomenon that strongly influences youth sport development. The RAE refers to a disproportionately high percentage in sport teams of athletes born early in the selection year. Our primary focus was to explore whether the RAE is supported by behavioral evidence in favor of better fitness-and especially cognitive-attentional functioning-of early as compared to late-born players. A cross-sectional study was conducted on 105 young athletes (u10, n = 52; 9.8 ± 0.3 years old, and u12, n = 53; 11.8 ± 0.2 years old) attending two youth elite soccer academies. Attentional functioning, anthropometrics, physical fitness, and game intelligence were compared across two Age Groups (u10 vs. u12) and four Birth Quarters (BQ1-BQ4). The RAE was statistically significant (p < 0.001), showing that about 50% of participants were born in the first quarter and 75% were born in the first half of the year. More importantly, U12 players outperformed u10 players in measures that were related to sustained attention (with faster and less variable responses; p < 0.001 and p < 0.05, respectively), and in all anthropometric measures (p < 0.001), physical-fitness capacities (p < 0.05). Crucially, neither the attentional measures, game intelligence, anthropometrics, nor physical fitness were affected by BQ (all ps > 0.1 and BF10 between 0.08 and 0.6, showing strong evidence for the null hypothesis). The present findings suggest that the early selection process that occurs during scouting in youth soccer academies offsets the age-related differences that could be anticipated in cognitive skills, anthropometrics, and physical abilities, due to growth and maturation. These birth asymmetries could lead teams to disregard later maturation athletes and athletes born later in the year inducing a larger dropout of those players with the consequent reduction in the talent pool.

#5 Similar risk of ACL graft revision for alpine skiers, football and handball players: the graft revision rate is influenced by age and graft choice
Reference: Br J Sports Med. 2019 Aug 9. pii: bjsports-2018-100020. doi: 10.1136/bjsports-2018-100020. [Epub ahead of print]
Authors: Ekeland A, Engebretsen L, Fenstad AM, Heir S
Summary: The risk of graft revision following ACL reconstruction may depend on the sport type the individuals are engaged in. The purpose of this study was to report the ACL graft revision rate in alpine skiers, football and handball players. Primary ACL reconstructions and graft revision data from 2004 to December 2016 were obtained from the Norwegian Cruciate Ligament Registry. The graft survival rates were calculated for individuals in each of the three sport types, for bone patellar tendon bone (BPTB) and hamstring tendons (HT) grafts separately, and related to age at primary operation and sex. A total of 711 grafts in 14 201 primary ACL reconstructions were revised (5.0%) after median 6 years, 3.8% in alpine skiers, 5.0% in soccer and 6.1% in handball players (p<0.001). Adjusted Cox regression showed similar ACL graft survival rates in the three groups. The HR for graft revision was 5 times higher for individuals aged ≤18 years than for those aged ≥35 years (p<0.001). The corresponding HR for graft type was 1.8 times higher for HT than for BPTB grafts (p<0.001), but 2.8 times higher for individuals aged ≤18 years (p<0.001). The 12 years survival of BPTB grafts was 96% compared with 93% for HT grafts (p <0.001). The revision rate for ACL grafts was similar among alpine skiers, football and handball players, and the results support the use of BPTB grafts in young athletes with closed growth zones in the knee.

#6 Functional Deficits in the Wrist and Finger Joints of Goalkeepers After 20 Years of Playing Recreational Football
Reference: Sportverletz Sportschaden. 2019 Aug;33(3):142-148. doi: 10.1055/a-0884-3334. Epub 2019 Aug 16.
Authors: Hilber F, Wiesenberg A, Kerschbaum M, Ernstberger A, Worlicek M, Nerlich M, Prantl L, Koch M, Krutsch V, Krutsch W
Summary: Long-term damage in the hip, knee and ankle joints of football players has been thoroughly discussed in the literature. Compared with outfield players, however, goalkeepers sustain injuries to the upper extremities five times more often. There is a lack of studies on long-term functional damage to the wrist and finger joints of football goalkeepers. The hypothesis was that repetitive micro-traumas and injuries lead to degenerative diseases in goalkeepers after 20 years of playing recreational soccer.  The personal histories, injury histories and clinical examination findings of the wrist and finger joints of 27 goalkeepers were compared with the findings obtained in a control group of outfield players. Goalkeepers were significantly more restricted in finger movement (p < 0.05) and experienced more pain and swelling (p < 0.05) as well as higher levels of instability (p < 0.05) in the wrist and finger joints than outfield players. Medical history and clinical findings indicate deficits in the hands of soccer goalkeepers and a high prevalence of joint and ligament injuries sustained to the fingers over the course of their sports activity. This necessitates specific strategies in the future to prevent injuries and long-term posttraumatic deficits.

#7 Editorial: Fatigue and Recovery in Football
Reference: Sports (Basel). 2019 Aug 13;7(8). pii: E192. doi: 10.3390/sports7080192.
Authors: Clarke N, Noon M
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#8 Play-by-Play Network Analysis in Football
Reference: Front Psychol. 2019 Jul 25;10:1738. doi: 10.3389/fpsyg.2019.01738. eCollection 2019.
Authors: Korte F, Link D, Groll J, Lames M
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Summary: This study identifies dominant and intermediary players in football by applying a play-by-play social network analysis (SNA) on 70 professional matches from the 1. and 2. German Bundesliga during the 2017/2018 season. SNA provides a quantification of the complex interaction patterns between players in team sports. So far, the individual contributions and roles of players in football have only been studied at match-level considering the overall passing of a team. In order to consider the real structure of football, a play-by-play network analysis is needed that reflects actual interplay. Moreover, a distinction between plays of certain characteristics is important to qualify different interaction phases. As it is often impossible to calculate well known network metrics such as betweenness on play-level, new adequate metrics are required. Therefore, flow betweenness is introduced as a new playmaker indicator on play-level and computed alongside flow centrality. The data on passing and the position of players was provided by the Deutsche Fußball Liga (DFL) and gathered through a semi-automatic multiple-camera tracking system. Central defenders are identified as dominant and intermediary players, however, mostly in unsuccessful plays. Offensive midfielders are most involved and defensive midfielders are the main intermediary players in successful plays. Forward are frequently involved in successful plays but show negligible playmaker status. Play-by-play network analysis facilitates a better understanding of the role of players in football interaction.

#9 A comparative study of core musculature endurance and strength between soccer players with and without lower extremity sprain and strain injury
Reference: Int J Sports Phys Ther. 2019 Jul;14(4):525-536.
Authors: Abdallah AA, Mohamed NA, Hegazy MA
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Summary: Lower extremity sprain and strain injury constitutes a large percentage of lower extremity injuries experienced by soccer players. Yet, very limited data exists on the association between core strength and endurance and this injury. The purpose of this study was to compare core muscle endurance and hip muscle strength between soccer players who experienced non-contact lower extremity sprain and/or strain injury during their season and those who did not. Additionally, the frequency of injury was correlated with core muscle endurance and hip strength, and endurance was used for predicting the risk for injury. Twenty-one (35.59%) athletes experienced non-contact lower extremity sprain and/or strain injury during the season. Fifty-nine male athletes (mean age 20.92 ± 4.08 years, mass 77.34 ± 12.02 kg and height 1.79 ± 0.06m) were tested. Prior to the start of the season, prone-bridge, side-bridge, trunk flexion and horizontal back extension hold times were recorded for endurance assessment and peak hip abductor and external rotator isokinetic torques for strength assessment. Prone-bridge and side-bridge hold times were significantly longer in the non-injured players when compared with the times of the injured players (p=0.043 & 0.008 for the prone-bridge and side-bridge, respectively). There were significant negative correlations between the frequency of injury and both prone-bridge (r=-0.324, p=0.007) and side-bridge (r=-0.385, p=0.003) hold times. Logistic regression analysis revealed that side-bridge hold time was a significant predictor of injury (OR=0.956, CI=0.925-0.989). Soccer players with non-contact lower extremity sprain and/or strain have less core endurance than non-injured players. Reduced core endurance is associated with increased incidence of injury. Improving side-bridge hold time, specifically, may reduce the risk for injury.

#10 High Risk of Further ACL Injury in a 10-Year Follow-up Study of ACL-Reconstructed Soccer Players in the Swedish National Knee Ligament Registry
Reference: Arthroscopy. 2019 Aug 19. pii: S0749-8063(19)30500-6. doi: 10.1016/j.arthro.2019.05.052. [Epub ahead of print]
Authors: Sandon A, Engström B, Forssblad M
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Summary: To follow up on soccer players 10 years after a primary anterior cruciate ligament (ACL) reconstruction to find out how many players returned to play soccer, what influenced their decision, and if there are any differences in additional ACL injuries (graft failure and/or contralateral ACL injury) between those who returned to play and those who did not. The study cohort consists of 1661 soccer players from the Swedish National Knee Ligament Registry. A questionnaire was sent to each player regarding their return to play and additional knee injuries that may have occurred 10 years after their primary ACL. The results are based on the 684 responders. Data such as age, sex, surgical procedural data, associated injuries, patient-reported outcome measures, and additional knee surgeries were collected from the registry. In this study, 51% returned to play soccer. For those who did not return to play, the primary reason was knee related (65.4% of the cases). The most common knee-related reasons for not returning were pain and/or instability (50%; n = 109), followed by fear of reinjury (32%; n = 69). Players who return to soccer have a significantly higher risk of additional ACL injury. Of the players who returned to play soccer, 28.7% (odds ratio [OR] 2.3, P < .001) had additional ACL injury, 9.7% (OR 2.9, P < .001) had a graft failure and 20.6% (OR 2.1, P < .001) had a contralateral ACL injury. Players that return to soccer have a significantly higher risk of sustaining further ACL injury. Only half of the soccer players return to play after ACL reconstruction, and in two-thirds of those who did not return, the reason was knee related. The high risk of sustaining additional knee injury is of serious concern to the player's future knee health and should be considered when deciding on a return to play.

#11 Phase Angle is Moderately Associated with Short-term Maximal Intensity Efforts in Soccer Players
Reference: Int J Sports Med. 2019 Aug 22. doi: 10.1055/a-0969-2003. [Epub ahead of print]
Authors: Nabuco HCG, Silva AM, Sardinha LB, Rodrigues FB, Tomeleri CM, Ravagnani FCP, Cyrino ES, Ravagnani CFC
Summary: This study examined the relationship between PhA and short-term maximal intensity efforts in soccer players, and was conducted in 99 male soccer players, ages 19-36 years. Bioelectrical impedance was used to assess body fat, fat free mass (FFM) and PhA (phase angle). Running Anaerobic Sprint Test (RAST) was used to evaluate physical performance. Food consumption was assessed through the 24-hour dietary recall method. Pearson correlation and multiple regressions were used for statistical analysis. Phase angle exhibited a positive relationship with maximum power (β=0.66; P<0.001), even after adjustment for the co-variables FFM and body fat (β=0.52; P=0.02). Phase angle was inversely related with fatigue index (β=- 0.61; P=0.04), even after adjusting for FFM (β=- 0.70; P=0.020). Our results indicated that independently of FFM and body fat, PhA was inversely associated with fatigue index and positively related with maximum power, revealing the PhA appeared as a valid predictor of fatigue.





Latest research in football - week 32 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Effects of Neuromuscular Training on Agility Performance in Elite Soccer Players
Reference: Front Physiol. 2019 Jul 23;10:947. doi: 10.3389/fphys.2019.00947. eCollection 2019.
Authors: Zouhal H, Abderrahman AB, Dupont G, Truptin P, Le Bris R, Le Postec E, Sghaeir Z, Brughelli M, Granacher U, Bideau B
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Summary: Agility in general and change-of-direction speed (CoD) in particular represent important performance determinants in elite soccer. The objectives of this study were to determine the effects of a 6-week neuromuscular training program on agility performance, and to determine differences in movement times between the slower and faster turning directions in elite soccer players. Twenty male elite soccer players from the Stade Rennais Football Club (Ligue 1, France) participated in this study. The players were randomly assigned to a neuromuscular training group (NTG, n = 10) or an active control (CG, n = 10) according to their playing position. NTG participated in a 6-week, twice per week neuromuscular training program that included CoD, plyometric and dynamic stability exercises. Neuromuscular training replaced the regular warm-up program. Each training session lasted 30 min. CG continued their regular training program. Training volume was similar between groups. Before and after the intervention, the two groups performed a reactive agility test that included 180° left and right body rotations followed by a 5-m linear sprint. The weak side was defined as the left/right turning direction that produced slower overall movement times (MT). Reaction time (RT) was assessed and defined as the time from the first appearance of a visual stimulus until the athlete's first movement. MT corresponded to the time from the first movement until the athlete reached the arrival gate (5 m distance). No significant between-group baseline differences were observed for RT or MT. Significant group x time interactions were found for MT (p = 0.012, effect size = 0.332, small) for the slower and faster directions (p = 0.011, effect size = 0.627, moderate). Significant pre-to post improvements in MT were observed for NTG but not CG (p = 0.011, effect size = 0.877, moderate). For NTG, post hoc analyses revealed significant MT improvements for the slower (p = 0.012, effect size = 0.897, moderate) and faster directions (p = 0.017, effect size = 0.968, moderate). Our results illustrate that 6 weeks of neuromuscular training with two sessions per week included in the warm-up program, significantly enhanced agility performance in elite soccer players. Moreover, improvements were found on both sides during body rotations. Thus, practitioners are advised to focus their training programs on both turning directions.

#2 A Meta-Analysis of Meta-Analyses of the Effectiveness of FIFA Injury Prevention Programmes in Soccer
Reference: Scand J Med Sci Sports. 2019 Aug 8. doi: 10.1111/sms.13535. [Epub ahead of print]
Authors: Al Attar WSA, Alshehri MA
Summary: FIFA has a Medical and Research Centre (F-MARC) which has designed a comprehensive programme targeting muscle strength, kinaesthetic awareness, and neuromuscular control during static and dynamic movements to decrease injury risk for soccer players. A number of meta-analyses now exist on how effective FIFA's programmes to prevent and reduce injury actually are, with various degrees of injury reduction reported. This research aimed to carry out a systematic review and to meta analyse the existing meta-analyses so that a conclusion can be drawn on how effective the injury programmes are. Relevant studies were identified by searching five databases for the period January 1990 till 1 July 2018. Results of each meta-analysis were combined together using risk ratios (RR) in a summary meta-analysis. QUOROM checklist and AMSTAR 2 assessment were used to assess the quality of reporting and methodology in the meta-analyses. Four meta-analyses met the inclusion criteria covering fifteen primary studies. All four meta-analyses scored quite highly on QUOROM, but two were rated by AMSTAR 2 as moderate quality and two were found to be of critically low quality. An overall risk reduction of 34% [RR= 0.66 (0.60 - 0.73)] for all injuries and a reduction of 29% [RR= 0.71 (0.63 - 0.81)] for injuries to the lower limbs were revealed by this meta-analysis of meta-analyses. Combining every previous meta-analysis into a single source in this paper produced decisive evidence that the risk of injuries while playing soccer is reduced as a result of FIFA's injury prevention programmes.

#3 A comparison of a GPS device and a multi-camera video technology during official soccer matches: Agreement between systems
Reference: PLoS One. 2019 Aug 8;14(8):e0220729. doi: 10.1371/journal.pone.0220729. eCollection 2019.
Authors: Pons E, García-Calvo T, Resta R, Blanco H, López Del Campo R, Díaz García J, Pulido JJ
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Summary: The aim of this study was to compare the agreement of the movement demands data during a soccer match (total distance, distance per minute, average speed, maximum speed and distance covered in different speed sectors) between an optical tracking system (Mediacoach System) and a GPS device (Wimu Pro). Participants were twenty-six male professional soccer players (age: 21.65 ± 2.03 years; height: 180.00 ± 7.47 cm; weight: 73.81 ± 5.65 kg) from FC Barcelona B, of whom were recorded a total of 759 measurements during 38 official matches in the Spanish second division. The Mediacoach System and the Wimu Pro were compared using the standardized mean bias, standard error of estimate, intraclass correlation coefficients (ICC), coefficient of variation (%), and the regression equation to estimate data for each variable. In terms of agreement between systems, the magnitude of the ICC was almost perfect (> 0.90-1.00) for all variables analyzed. The coefficient of the variations between devices was close to zero (< 5%) for total distance, distance per minute, average speed, maximum speed, and walking and jogging, and between 9% and 15% for running, intense running, and sprinting at low and at high intensities. It can be observed that, compared to Wimu Pro the Mediacoach System slightly overestimated all the variables analyzed except for average speed, maximum speed, and walking variables. In conclusion, both systems can be used, and the information they provide in the analyzed variables can be interchanged, with the benefits implied for practitioners and researchers.

#4 Genomic analysis reveals association of specific SNPs with athletic performance and susceptibility to injuries in professional soccer players
Reference: J Cell Physiol. 2019 Aug 7. doi: 10.1002/jcp.29118. [Epub ahead of print]
Authors: La Montagna R, Canonico R, Alfano L, Bucci E, Boffo S, Staiano L, Fulco B, D'Andrea E, De Nicola A, Maiorano P, D'Angelo C, Chirico A, De Nicola A, Giordano A
Summary: The development of specific and individualized training programs is a possible way to improve athletic performance and minimize injuries in professional athletes. The information regarding the sport's physical demands and the athletes' physical profile have been, so far, considered as exhaustive for the design of effective training programs. However, it is currently emerging that the genetic profile has to be also taken into consideration. By merging medical and genetic data, it is thus possible to identify the athlete's specific attitude to respond to training, diet, and physical stress. In this context, we performed a study in which 30 professional soccer players, subjected to standard sport medical evaluation and practices, were also screened for genetic polymorphism in five key genes (ACTN3, COL5A1, MCT1, VEGF, and HFE). This genetic analysis represents the central point of a multidisciplinary method that can be adopted by elite soccer teams to obtain an improvement in athletic performance and a concomitant reduction of injuries by tailoring training and nutritional programs. The genetic fingerprinting of single athletes led to the identification of two performance-enhancing polymorphisms (ACTN3 18705C>T, VEGF-634C>G) significantly enriched. Moreover, we derived a genetic model based on the gene set analyzed, which was tentatively used to reduce athletes' predisposition to injuries, by dictating a personalized nutrition and training program. The potential usefulness of this approach is concordant with data showing that this team has been classified as the healthiest and least injured team in Europe while covering the highest distance/match with the highest number of high-intensity actions/match.

#5 Ten-Year Epidemiology of Ankle Injuries in Men's and Women's Collegiate Soccer Players
Reference: J Athl Train. 2019 Aug 7. doi: 10.4085/1062-6050-144-18. [Epub ahead of print]
Authors: Gulbrandsen M, Hartigan DE, Patel K, Makovicka J, Tummala S, Chhabra A
Summary: Data from the National Collegiate Athletic Association (NCAA) Injury Surveillance Program (ISP) has indicated that ankle injuries are the most common injuries among NCAA soccer players. The objective was to review 10 years of NCAA-ISP data for soccer players' ankle injuries to understand how the time period (2004-2005 through 2008-2009 versus 2009-2010 through 2013-2014), anatomical structure injured, and sex of the athlete affected the injury rate, mechanism, and prognoses. The NCAA-ISP was queried for men's and women's soccer ankle data from 2004 to 2014. Ankle injury rates were calculated on the basis of injuries per 1000 athlete-exposures. Rate ratios (RRs) were used to compare injury rates. Injury proportion ratios (IPRs) were used to compare injury characteristics. When compared with the 2004-2005 through 2008-2009 seasons, the 2009-2010 through 2013-2014 seasons showed a similar rate of injuries (RR = 0.94, 95% confidence interval [CI] = 0.85, 1.04) but fewer days missed (P < .001) and fewer recurrent injuries (IPR = 0.55, 95% CI = 0.41, 0.74). The 4 most common ankle injuries, which accounted for 95% of ankle injuries, were lateral ligament complex tears (65.67%), tibiofibular ligament (high ankle) sprains (10.3%), contusions (10.1%), and medial (deltoid) ligament tears (9.77%). Of these injuries, high ankle sprains were most likely to cause athletes to miss ≥30+ days (IPR = 1.9, 95% CI = 1.24, 2.90). Men and women had similar injury rates (RR = 1.02, 95% CI = 0.94, 1.11). Men had more contact injuries (IPR = 1.28, 95% CI = 1.16, 1.41) and contusion injuries (IPR = 1.34, CI = 1.03, 1.73) but fewer noncontact injuries (IPR = 0.86, 95% CI = 0.78, 0.95) and lateral ligamentous complex injuries (IPR = 0.92, 95% CI = 0.86, 0.98). Although the rate of ankle injuries did not change between the 2004-2005 through 2008-2009 seasons and the 2009-2010 through 2013-2014 seasons, the prognoses improved. Among the 4 most common ankle injuries, high ankle sprains resulted in the worst prognosis. Overall, male and female NCAA soccer players injured their ankles at similar rates; however, men were more likely to sustain contact injuries.

#6 Power training in elite young soccer players: Effects of using loads above or below the optimum power zone
Reference: J Sports Sci. 2019 Aug 7:1-7. doi: 10.1080/02640414.2019.1651614. [Epub ahead of print]
Authors: Loturco I, Pereira LA, Reis VP, Bishop C, Zanetti V, Alcaraz PE, Freitas TT, Mcguigan MR
Summary: This study aimed to examine the effects of two jump squat (JS) training programs involving different loading ranges in under-20 soccer players during a preseason period. Twenty-three elite young soccer players performed sprint speed (at 5-, 10-, and 20-m), change-of-direction (COD) speed, JS peak-power (PP), and countermovement jump (CMJ) tests pre and post four weeks of training. Athletes were pair-matched in two groups according to their optimum power loads (OPL) as follows: lower than OPL (LOPL; athletes who trained at a load 20% lower than the OPL) and higher than OPL (HOPL; athletes who trained at a load 20% higher than the OPL). Magnitude-based inferences were used to compare pre- and post-training measures. Meaningful increases in the PP JS were observed for both groups. Likely and possible improvements were observed in the 5- and 10-m sprint velocity in the LOPL group. Meanwhile, possible and likely improvements were observed in the CMJ, 5- and 10-m sprint velocity, and COD speed in the HOPL group. Overall, both training schemes induced positive changes in athletic performance. Soccer coaches and sport scientists can implement the JS OPL-based training schemes presented here, either separately or combined, to improve the physical performance of youth soccer players

#7 Coaches' Emotional Intelligence and Reactive Behaviors in Soccer Matches: Mediating Effects of Coach Efficacy Beliefs
Reference: Front Psychol. 2019 Jul 10;10:1629. doi: 10.3389/fpsyg.2019.01629. eCollection 2019.
Authors: Teques P, Duarte D, Viana J
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Summary: In the last 10 years, emotional intelligence (EI) has become a current issue of research in psychology, and there are indicators to consider that EI should be analyzed to help the coach to behave effectively during competitions. According to Boardley's (2018) revised model of coaching efficacy, coaches' EI is predictive of their efficacy beliefs, which, in turn, is predictive of coaching behavior. However, little is known about the mediating effects of coaching efficacy dimensions on the relationships between coach's EI and reactive behaviors in competitive settings. Thus, the purpose of this study is to examine mediating effects of coaching efficacy dimensions on the relationship between EI and coaches' reactive behaviors during a game using a multimethod approach. Participants were 258 coaches of youth football players aged 9 to 17 years old. Observations in situ using Coaching Behavior Assessment System (CBAS) were carried on 258 football games during two seasons. At the end of each game, coaches completed the Wong and Law Emotional Intelligence Scale (WLEIS) and the Coaching Efficacy Scale (CES). Structural equation modeling (SEM) analyses revealed that motivation efficacy and character building mediated the relationship between regulation of emotion and positive and negative coaches' reactions during game. Specifically, motivation efficacy mediated the association between regulation of emotion and positive coaches' reactions, and the relationship between regulation of emotion and negative coaches' reactions were mediated by motivation efficacy and character building. In addition, coaching level moderated the relationships between EI, self-efficacy and coaches' reactive behaviors. Findings of the present study showed that coaching efficacy dimensions (i.e., motivation efficacy and character building) that have the capacity to influence their confidence in ability to affect the psychological mood and positive attitude of athletes, transfer the effects of EI (i.e., regulation of emotion) on coaches' verbal reactions during a youth soccer game. Specifically, a coach who feels competent to regulate their own emotions would perceive high beliefs of efficacy to motivate and to build character of their athletes, and this insight has an impact on their positive verbal reactions in response to athletes' performances.

#8 Ratings of perceived recovery and exertion in elite youth soccer players: Interchangeability of 10-point and 100-point scales
Reference: Physiol Behav. 2019 Aug 1;210:112641. doi: 10.1016/j.physbeh.2019.112641. [Epub ahead of print]
Authors: Clemente FM, Rabbani A, Araújo JP
Summary: The purpose of this study was to examine the interchangeability of a new perceived recovery status scale (PRS) of 100 points through a comparison to the original 10-point version. This study also aimed to test the interchangeability of CR100 scale (Borg's rate of perceived exertion scale) in comparison to the CR10. Twenty-five male elite youth soccer players (age: 18.0 ± 0.5 years old; body mass: 70.1 ± 6.7 kg; height: 177.8 ± 6.5 cm; experience: 11.7 ± 1.2 years) from the same team competing in the first national under-19 competition participated in this study. During two consecutive weeks, the players completed PRS (both 10- and 100-points) and CR10 and CR100 scales. Nearly perfect relationships were observed between 0-to-10 and 0-to-100 scales, both for recovery status (r = 0.96, confidence interval [0.95;0.97]) and ratings of perceived exertion (RPE) (r = 0.97 [0.97;0.98]). Moreover, almost 95% of individuals showed nearly-perfect-to-perfect associations between 0-to-10 and 0-to100 in terms of RPE and recovery scales. Both a PRS of 100 points and CR100 can be used interchangeably with a PRS of 10 points and CR10, respectively.

#9 Inter-rater Reliability in Assessing Exercise Fidelity for the Injury Prevention Exercise Programme Knee Control in Youth Football Players
Reference: Sports Med Open. 2019 Aug 7;5(1):35. doi: 10.1186/s40798-019-0209-9.
Authors: Ljunggren G, Perera NKP, Hägglund M
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Summary: To receive maximum benefits from injury prevention exercise programmes (IPEP) such as Knee Control, players need to perform the exercises as prescribed. But, exercise fidelity in IPEPs is seldom evaluated. We developed a checklist to assess exercise fidelity in the Knee Control IPEP, and the primary aim was to evaluate its inter-rater reliability. The secondary aim was to study Knee Control exercise fidelity in youth football players and compare sex differences. This observational study included 11 teams with male and female youth players (11-18 years). On average, the players trained with the Knee Control IPEP for 7 weeks (SD 1.4, range 6-10 weeks). After the training period, two physiotherapists attended a team training session to observe players executing exercises and individually assessed their performance of these exercises as correct or incorrect based on standardised criteria set in the fidelity checklist. Agreement between observers was assessed using Cohen's kappa coefficient. The observers agreed on 144 out of 160 (90%) observations (Kappa = 0.80, substantial agreement). Both observers agreed on correct exercise performance for 69 out of 144 observations (exercise fidelity 48%). Exercise fidelity was higher in females (56%) than males (40%), but the difference was not statistically significant (p = 0.18). The Knee Control exercise fidelity checklist had high inter-rater reliability with substantial agreement. The exercise fidelity was low, which could hamper the preventive effects of an IPEP. Understanding the reasons for low exercise fidelity is important and more effort should focus on increasing exercise fidelity alongside the implementation of IPEPs.

#10 Effects of Linear Versus Changes of Direction Repeated Sprints on Intermittent High Intensity Running Performance in High-level Junior Football Players over an Entire Season: A Randomized Trial
Reference: Sports (Basel). 2019 Aug 6;7(8). pii: E189. doi: 10.3390/sports7080189.
Authors: Sagelv EH, Selnæs I, Pedersen S, Pettersen SA, Randers MB, Welde B
Summary: Changes of direction (COD) repeated sprints (RSs) might have greater relevance to football than linear RSs. We aimed to compare the effects of linear and COD RSs on intermittent high intensity running (HIR) over an entire season. In total, 19 high-level male football players (16-19 years) randomly performed linear RSs or COD RSs twice a week during their competitive season over 22 weeks. Yo-Yo intermittent recovery test level 2 (Yo-Yo IR2), and 10- and 20-m sprint was assessed pre-, mid- (11 weeks), and post-intervention (22 weeks). Maximal oxygen uptake (VO2max) was assessed pre- and post-intervention. There was no interaction effect (time x group) in Yo-Yo IR2 (p = 0.36, pη2 = 0.06) or sprint tests (10 m: p = 0.55, pη2 = 0.04, 20 m: p = 0.28 pη2 = 0.08), and no change differences between groups. There was a main effect of time for Yo-Yo IR2 (p = 0.002, pη2 = 0.31) but not in sprints or VO2max. Linear and COD RS exercise twice a week over 22 weeks equally improves intermittent HIR performance but does not improve sprint time or aerobic power in high-level junior football players. However, due to our two-armed intervention, we cannot exclude possible effects from other exercise components in the players' exercise program.

#11 Rescheduling Part 2 of the 11+ reduces injury burden and increases compliance in semi-professional football
Reference: Scand J Med Sci Sports. 2019 Aug 3. doi: 10.1111/sms.13532. [Epub ahead of print]
Authors: Whalan M, Lovell R, Steele JR, Sampson JA
Summary: Although the 11+ programme has been shown to reduce injuries in sub-elite football, programme compliance is typically poor, suggesting that strategies to optimize delivery are necessary. This study investigated the effect of rescheduling Part 2 of the three-part 11+ programme on programme effectiveness. Twenty-five semi-professional football clubs were randomly allocated to either a Standard-11+ (n=398 players) or P2post group (n=408 players). Both groups performed the 11+ programme at least twice a week throughout the 2017 football season. The Standard-11+ group performed the entire 11+ programme before training activities commenced, whereas the P2post group performed Parts 1 and 3 of the 11+ programme before and Part 2 after training. Injuries, exposure and individual player 11+ dose were monitored throughout the season. No significant between group difference in injury incidence rate (P2post vs Standard-11+ = 11.8 vs 12.3 injuries/1000 h) was observed. Severe time loss injuries >28 days (33 vs 58 injuries; p<0.002) and total days lost to injury (4303 vs 5815 days; p<0.001) were lower in the P2post group. A higher 11+ programme dose was observed in the P2post (29.1 doses; 95% CI 27.9-30.1) versus Standard-11+ group (18.9 doses; 95% CI 17.6 -20.2; p<0.001). In semi-professional football, rescheduling Part 2 of the 11+ programme to the end of training maintained the effectiveness of the original 11+ programme to reduce injury incidence. Importantly, rescheduling Part 2 improved player compliance and reduced the number of severe injuries and total injury burden thereby enhancing effectiveness of the 11+ programm

#12 Performance Activities and Match Outcomes of Professional Soccer Teams during the 2016/2017 Serie A Season
Reference: Medicina (Kaunas). 2019 Aug 12;55(8). pii: E469. doi: 10.3390/medicina55080469.
Authors: Longo UG, Sofi F, Candela V, Dinu M, Cimmino M, Massaroni C, Schena E, Denaro V
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Summary: Soccer is the most popular sport in the world. To describe athletic performance, match statistics, and their relationships with the probability of achieving the first positions of the final ranking in the Italian football league "Serie A", season 2016/2017. Analyses comprised all the matches played by the 20 teams of the "Serie A" championship during the season 2016-2017. Indicators of athletic performance (total distance covered in km, jogging, running and sprint activities, and average speed) and match statistics (total shots, shots on target, goal attempts, assists, turnovers, and steals) were obtained from the Italian football league. Analyses of performance activities according to the final ranking showed no significant differences for the total distance covered and speed, while a statistically significant difference (p < 0.05) among teams was observed for jogging, running and sprint activities. In regard to match statistics, all the parameters investigated were significantly different among the teams. By grouping teams into four subgroups (those who qualified for the Champions League, those who qualified for the Europe League, those who ranked intermediate positions and those who relegated from the "Serie A" league), the percentage of jogging, running and sprint activities, as well as match statistics were significantly different among groups, with a downward trend for total shots, shots on target, goal attempts, assists, and turnovers. The logistic regression analysis revealed that sprint activities as well as total shots, shots on target, goal attempts, and assists higher than the 3rd tertile of their distribution were associated with a higher probability of reaching the first three positions of the final ranking. An increased probability to achieve the first positions of the final ranking in the Italian football league "Serie A" seemed to be mainly related to sprint activity, goal attempts, total shots, shots on target and assists.





Latest research in football - week 31 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Field Methods to Estimate Fat-free Mass in International Soccer Players
Reference: Int J Sports Med. 2019 Jul 31. doi: 10.1055/a-0969-8591. [Epub ahead of print]
Authors: Nuñez FJ, Munguia-Izquierdo D, Petri C, Suarez-Arrones L
Summary: Based on the high financial and logistical costs associated with the assessment of body composition with dual-energy X-ray absorptiometry (DXA), this study determined which field method has the best correlation with DXA data, and developed an equation to estimate fat-free mass (FFM) using the field anthropometric data in international soccer players. A total of 17 international soccer players participated in this study. DXA values provided a criterion measure of FFM. Correlation coefficients, biases, limits of agreement, and differences were used as validity measures, and regression analyses were used to develop the prediction equation. All field methods used to obtain FFM data showed positive correlations (r from 0.90-0.96) with DXA. Only the equation developed by Deurenberg et al. [6] showed no differences from DXA with a low bias. The main strength of this study was providing a valid and accurate equation to estimate FFM specifically in international soccer players.

#2 Prospective Evaluation of Injuries occurred during the Brazilian Soccer Championship in 2016
Reference: Rev Bras Ortop (Sao Paulo). 2019 May;54(3):329-334. doi: 10.1055/s-0039-1692429. Epub 2019 Jun 27.
Authors: Netto DC, Arliani GG, Thiele ES, Cat MNL, Cohen M, Pagura JR
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Summary: The purpose was to identify the incidence, the prevalence, the characteristics, and the possible risk factors for injuries occurring during the matches of the Brazilian Soccer Championship. A prospective study was carried out to collect data on the injuries that occurred during the 2016 Brazilian Soccer Championship. Lesions were recorded by the physician responsible for each team through an online software. Among the 864 athletes included in the study, 231 (26.7%) of the players presented some injury during the tournament. In total, 312 injuries were recorded during the Brazilian Soccer Championship, with an average of 0.82 injuries per game. The incidence of injuries was 24.9 injuries per 1,000 match hours. Midfielders and forwards presented, respectively, an injury risk 3.6 and 2.4 times higher than goalkeepers. The prevalence and incidence of lesions were, respectively, 26.7% and 24.9 injuries per 1,000 match hours. The most frequently affected body segment was the lower limbs (76.3%), and the athletes acting in midfield and forward positions were the most affected. Moreover, the greater prevalence of injuries occurred in the first part of the championship.

#3 Imaging Assessment of the Pubis in Soccer Players
Reference: Rev Bras Ortop (Sao Paulo). 2019 Apr;54(2):118-127. doi: 10.1016/j.rbo.2017.12.012. Epub 2019 May 10.
Authors: Todeschini K, Daruge P, Bordalo-Rodrigues M, Pedrinelli A, Busetto AM
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Summary: The purpose was to compare the accuracy of ultrasound (US) with that of magnetic resonance imaging (MRI) in the detection of aponeurosis lesions of the rectus abdominis/adductor longus muscles, to study the characteristics of the athletes and imaging findings associated with pubalgia, and to demonstrate the importance of each method in evaluating this condition. The present study was conducted from 2011 to 2016 with 39 professional soccer players: 15 with pubalgia and 24 without pubalgia. Age, field position, body mass index (BMI), weekly training load, career length, and history of thigh/knee injury and lower back pain were recorded. The following tests were performed: radiographs (anteroposterior view of the pelvis in standing and flamingo positions) to evaluate hip impingement, sacroiliac joint, and pubic symphysis instability; US to analyze the common aponeurosis of the rectus abdominis/adductor longus muscles and inguinal hernias; and MRI for pubic bone degenerative alterations and edema, and lesions in the adductor and rectus abdominis muscles and their aponeurosis. There was an association between pubalgia, high BMI ( p  = 0.032) and muscle alterations ( p  < 0.001). Two patients with pubalgia had inguinal hernias and one patient with pubalgia and two controls had sports hernias. Pubic degenerative changes were frequent in both groups. Aponeurosis lesions were more frequent in patients with pain. The US detection had 44.4% sensitivity and 100% specificity. The evaluation of athletic pubalgia should be performed with radiography, US, and MRI. High BMI, muscle injuries, geodes, and osteophytes are findings associated with pubalgia; US has low sensitivity to detect injuries of the common aponeurosis of the rectus abdominis/adductor longus muscles.

#4 Eighty-two per cent of male professional football (soccer) players return to play at the previous level two seasons after Achilles tendon rupture treated with surgical repair
Reference: Br J Sports Med. 2019 Jul 30. pii: bjsports-2019-100556. doi: 10.1136/bjsports-2019-100556. [Epub ahead of print]
Authors: Grassi A, Rossi G, D'Hooghe P, Aujla R, Mosca M, Samuelsson K, Zaffagnini S
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Summary: The purpose was to evaluate the time to return to playing following acute Achilles tendon rupture (ATR) and surgical repair in professional male football (soccer) players. Professional male football (soccer) players who sustained an ATR and underwent surgical repair were identified through internet-based injury reports from January 2008 to August 2018. Only League 1 and 2 players with injuries who had at least 1 year of follow-up from the search date were included. Injury history and time to return to play were retrieved from the public platform For athletes who competed for at least two seasons after returning to play, re-ruptures and number of matches played were reported. 118 athletes (mean age 27.2±7.2 years) were included. 113 (96%) returned to unrestricted practice after a mean of 199±53 days, with faster recovery in players involved in national teams. Return to competition was after a mean of 274±114 days. In the 76 athletes with at least two seasons of follow-up, 14 (18%) did not compete at the pre-injury level during the two seasons following the index injury. Six players (8%) sustained a re-rupture within the first two seasons after return to play; four re-ruptures were in footballers who returned to play <180 days after injury. Age >30 years and re-ruptures had higher odds ratios of not returning to the same level of play. 96% of professional male football players who underwent surgery to repair an ATR returned to unrestricted practice and then competition after an average time of 7 and 9 months, respectively. However, 18% did not return to the same level of play within the two seasons following their return, with a higher risk in those experiencing a re-rupture.

#5 Test-Retest Reliability of Skill Tests in the F-MARC Battery for Youth Soccer Players
Reference: Percept Mot Skills. 2019 Jul 30:31512519866038. doi: 10.1177/0031512519866038. [Epub ahead of print]
Authors: Padrón-Cabo A, Rey E, Pérez-Ferreirós A, Kalén A
Summary: This study aimed to evaluate the test-retest reliability of soccer skill tests belonging to the F-MARC test battery. To avoid bias during talent identification and development, coaches and scouts should be using reliable tests for assessing soccer-specific skills in young male players. Fifty-two U-14 outfield male soccer players performed F-MARC soccer skill tests on two occasions, separated by 7 days. After familiarization, we administered two trial sessions of five skill tests: speed dribbling, juggling, shooting, passing, and heading. We assessed absolute reliability by expressing the standard error of measurement as a coefficient of variation with 95% limits of agreement, and we assessed relative reliability with the intraclass correlation coefficient and with Pearson's correlation (r). The results demonstrated satisfactory relative and absolute reliability for speed dribbling, right foot juggling, short passing, shooting a dead ball right, shooting from a pass, heading in front, and heading right. However, reliability values for left foot juggling, chest-head-foot juggling, head-left-foot-right foot-chest-head juggling, long pass, and shooting a dead ball left tests were not strong enough to suggest their usage by coaches in training or sport scientists in research.

#6 Range of Motion and Injury Occurrence in Elite Spanish Soccer Academies. Not Only a Hamstring Shortening-Related Problem
Reference: J Strength Cond Res. 2019 Jul 29. doi: 10.1519/JSC.0000000000003302. [Epub ahead of print]
Authors: Sanz A, Pablos C, Ballester R, Sánchez-Alarcos JV, Huertas F
Summary: Age-related development of range of motion (ROM) during an active hip flexion (active straight leg raise) and its relationship with hamstring injury occurrence were examined in 1657 young male soccer players (9-18 years of age). Age-related differences in ROM showed a significant decrease from U9 to U11 (p = 0.001), from U11 to U13 (p < 0.005), and from U9 to U13 (p < 0.001), whereas ROM increased from U13 to U15 and from U13 to U18 (both p's < 0.001). Interestingly, younger and older players reached similar ROM values (U9-U18, p = 0.87). Higher ROM was found in dominant than nondominant leg in all age groups (all ps < 0.001). No differences related to playing position were found on ROM (all ps > 0.478). During the follow-up period (11 months) 97 hamstring injuries were reported showing higher rates in the older age groups (p < 0.001) and outfield players (p < 0.001). Remarkably, no differences in ROM average were found between injured players and noninjured players (p = 0.152). Our results suggest that ROM during hip flexion does not only depend on the hamstrings shortening but also on the variables related to joint stability, motor control, and hip flexor muscle weakness. Sport scientists in youth sport soccer academies should develop age-specific screening and action plans to develop strength, motor control, and flexibility to optimize ROM and reduce injuries from the grassroots stages.

#7 Comparing the magnitude and direction of asymmetry during the squat, countermovement and drop jump tests in elite youth female soccer players
Reference: J Sports Sci. 2019 Jul 29:1-8. doi: 10.1080/02640414.2019.1649525. [Epub ahead of print]
Authors: Bishop C, Pereira LA, Reis VP, Read P, Turner AN, Loturco I
Summary: The aims of the present study were to provide an in-depth comparison of inter-limb asymmetry and determine how consistently asymmetry favours the same limb during different vertical jump tests. Eighteen elite female under-17 soccer players conducted unilateral squat jumps (SJ), countermovement jumps (CMJ) and drop jumps (DJ) on a portable force platform, with jump height, peak force, concentric impulse and peak power as common metrics across tests. For the magnitude of asymmetry, concentric impulse was significantly greater during the SJ test compared to CMJ (p = 0.019) and DJ (p = 0.003). No other significant differences in magnitude were present. For the direction of asymmetry, Kappa coefficients revealed fair to substantial levels of agreement between the SJ and CMJ (Kappa = 0.35 to 0.61) tests, but only slight to fair levels of agreement between the SJ and DJ (Kappa = -0.26 to 0.18) and CMJ and DJ (Kappa = -0.13 to 0.26) tests. These results highlight that the mean asymmetry value may be a poor indicator of true variability of between-limb differences in healthy athletes. The direction of asymmetry may provide a useful monitoring tool for practitioners in healthy athletes, when no obvious between-limb deficit exists.

#8 Relative age and maturation selection biases in academy football
Reference: J Sports Sci. 2019 Jul 31:1-9. doi: 10.1080/02640414.2019.1649524. [Epub ahead of print]
Authors: Hill M, Scott S, Malina RM, McGee D, Cumming SP
Summary: This study examined the simultaneous effects of relative age and biological maturity status upon player selection in an English professional soccer academy. A total of 202 players from the U9 to U16 age groups, over an eight-year period (total of 566 observations), had their relative age (birth quarter) and biological maturity (categorised as late, on-time or early maturing based upon the Khamis-Roche method of percentage of predicted adult height at time of observation) recorded. Players born in the first birth quarter of the year (54.8%) were over-represented across all age groups. A selection bias towards players advanced in maturity status for chronological age emerged in U12 players and increased with age; 0% of players in the U15 and U16 age group were categorised as late maturing. A clear maturity selection bias for early maturing players was, however, only apparent when the least conservative criterion for estimating maturity status was applied (53.8% early and 1.9% late maturing in the U16 age group). Professional football academies need to recognise relative age and maturation as independent constructs that exist and operate independently. Thus, separate strategies should perhaps be designed to address the respective selection biases, to better identify, retain and develop players.

#9 High return to competition rate following ACL injury - A 10-year media-based epidemiological injury study in men`s professional football
Reference: Eur J Sport Sci. 2019 Jul 29:1-15. doi: 10.1080/17461391.2019.1648557. [Epub ahead of print]
Authors: Werner K, Clemens M, Volker K, Peter A, Tobias T, Karen AF, Tim M
Summary: Ruptures of the anterior cruciate ligament (ACL) typically occur in professional football and epidemiological data about longitudinal injury development is needed. The purpose was to This practice-driven investigation of media-derived ACL data provides information about professional football over 10 years. Injury registration was based on "kicker" sports magazine information that have been recorded over one decade in a standardized manner. Only ACL ruptures in the first German football league were included when they could be verified by a second reliable source. Fifty-seven primary ACL ruptures were verified in the first German football league during the seasons 2007/08 to 2016/17. Among them, 6 re-injuries were found. Mean age at the time of injury was 24.8 years (SD 3.8). 31% (n = 20) of ACL ruptures occurred at the beginning of the season in August or September (p = 0.02). Mean time of RTC after primary ACL ruptures was 226.7 days (SD: 93.5) and 245.6 days (SD: 45.4) after re-injury. Although 62 (98%) players returned to football after injury and only one player immediately finished his career, 54.9% of the affected individuals played 3 years after the ACL rupture in the same league. ACL ruptures lead to longer absence than 7 months from football but does not give reason for immediate career-ending. The decrease in playing level after 3 years illustrate the serious consequences of ACL ruptures in football. Media-based injury reports may provide interesting information.

#10 Gender-dependent evaluation of football as medicine for prediabetes
Reference: Eur J Appl Physiol. 2019 Sep;119(9):2011-2024. doi: 10.1007/s00421-019-04188-5. Epub 2019 Jul 26
Authors: Mohr M, Skoradal MB, Andersen TR, Krustrup P
Summary: Training intensity and health effects of football were investigated gender specifically in individuals with prediabetes. Participants with prediabetes (age 60 ± 6 years) were randomised into a football and dietary advice group (FD-men n = 13 and FD-women n = 14) or a dietary advice only group (D-men n = 12 and D-women n = 11). FD performed football training (twice/week for 16 weeks), while both groups received dietary advice. Body composition, bone variables, blood pressure, blood lipid profile and peak oxygen uptake (VO2peak) were determined pre- and post-intervention. Mean heart rate during football training was 79 ± 2 and 80 ± 3% HRmax for FD-men and FD-women, respectively, with peak heart rate values of 96 ± 1 and 97 ± 2% HRmax, with no gender differences. VO2peak increased more (P < 0.05) in FD-men and FD-women than in D-men and D-women. However, relative delta change in VO2peak was 21 ± 14% in FD-women, which was greater (P < 0.05) than in FD-men (11 ± 12%). Reduction in SBP and DBP, respectively, was similar in FD-men (- 10.8 ± 13.0 and - 7.3 ± 11.8 mmHg) and FD-women (- 11.3 ± 11.0 and - 7.1 ± 6.2 mmHg), with within-gender differences for men. Total plasma cholesterol and LDL cholesterol decreased (P < 0.05) by - 0.7 ± 1.1 and - 0.5 ± 0.9 mmol L-1, respectively, in FD-women and - 0.2 ± 0.4 and - 0.2 ± 0.3 mmol L-1 in FD-men, with no significant gender differences (P = 0.08). Body fat content was lowered (P < 0.05) by 3 and 4%-points in FD-men and FD-women, respectively. Gender-mixed football training combined with dietary advice causes broad-spectrum health effects for men and women with prediabetes, with minor gender-specific differences. Thus, the intensity and training-induced effects of football training are also high for elderly women with prediabetes.

#11 Characteristics of plantar pressure distribution in elite male soccer players with or without history of proximal fifth metatarsal fracture: a case-control study
Reference: J Phys Ther Sci. 2019 Jul;31(7):530-535. doi: 10.1589/jpts.31.530. Epub 2019 Jul 2.
Authors: Kuzuyama M, Perrier J, Kusaki Y, Sato K, Yamaura I, Tsuchiya A
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Summary: Studies have demonstrated a relationship between plantar pressure distribution and proximal fifth metatarsal fracture. We aimed to investigate the plantar pressure patterns of soccer players with or without a history of proximal fifth metatarsal fracture. Fifty-one male soccer players (31 professional, 20 high-school) participated in this study (mean age, weight, and height ± SD: 21.1 ± 4.7 years, 68.8 ± 5.8 kg, and 175.4 ± 5.9 cm, respectively). Seven of them had a history of proximal fifth metatarsal fracture before this study (the fracture group) and 44 had no history of fracture (the control group). A Win-Pod (Medicapteurs) platform was used to measure foot pressure forces. The center of plantar pressure was measured during double and single-limb stances for 25 seconds. Fifth metatarsal pressure and the center of plantar pressure angle was calculated from the walking footprint. The calculated data were compared between the fracture group and the control group. [Results] Comparisons between the fracture and control groups in terms of morphology and the center of plantar pressure length showed no significant differences. However, the fifth metatarsal pressure and the center of plantar pressure angle were significantly higher in the fracture group. [Conclusion] The results of this study revealed that players with excessive loading in the lateral areas of the foot while walking have a risk of developing proximal fifth metatarsal fracture.

#12 Effects of Bio-Banding upon Physical and Technical Performance during Soccer Competition: A Preliminary Analysis
Reference: Sports (Basel). 2019 Aug 14;7(8). pii: E193. doi: 10.3390/sports7080193.
Authors: Abbott W, Williams S, Brickley G, Smeeton NJ
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Summary: Bio-banded competition has been introduced to address the variation in physical maturity within soccer. To date, no research has investigated the effect of bio-banded competition relative to chronological competition. The current study investigated the effect of bio-banding upon physical and technical performance in elite youth soccer athletes. Twenty-five male soccer athletes (11-15 years) from an English Premier League soccer academy participated in bio-banded and chronological competition, with physical and technical performance data collected for each athlete. Athletes were between 85-90% of predicted adult stature, and sub-divided into early, on-time and late developers. For early developers, significantly more short passes, significantly less dribbles and a higher rating of perceived exertion (RPE) were evident during bio-banded competition compared to chronological competition (p < 0.05). Significantly more short passes and dribbles, and significantly fewer long passes were seen for on-time developers during bio-banded competition (p < 0.05). For late developers, significantly more tackles, and significantly fewer long passes were evident during bio-banded competition (p < 0.05). No significant differences in physical performance were identified between competition formats. Results demonstrated that bio-banded competition changed the technical demand placed upon athletes compared to chronological competition, without reducing the physical demands. Bio-banded competition can be prescribed to athletes of differing maturation groups dependent upon their specific developmental needs.





Latest research in football - week 30 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Are acceleration and cardiovascular capacities related to perceived load in professional soccer players?
Reference: Res Sports Med. 2019 Jul 21:1-15. doi: 10.1080/15438627.2019.1644642. [Epub ahead of print]
Authors: Azcárate U, Los Arcos A, Jiménez-Reyes P, Yanci J
Summary: This study aims at assessing physical fitness performance and its relationship with the differential ratings of perceived exertion of training load (dRPE TL) and match load (dRPE ML) in a Spanish professional soccer team at the beginning of several in-season periods: 1-4 weeks, 5-8 weeks and 1-8 weeks. Performance and mechanical variables over the acceleration phase, as well as cardiovascular performance variables were evaluated in 20 male professional soccer players of a team competing in the Spanish Second Division League. Moreover, dRPE TL and dRPE ML were quantified. The dRPE TL showed negative and large associations between both maximal aerobic speed (MAS) and maximal oxygen consumption (VO2max) (from r = -0.53; ± 0.06 to r = -0.53; ± 0.05 95% CL, p = 0.035 to 0.036) and RPEres TL values throughout the 5-8 and 1-8 week periods. Furthermore, dRPE ML positive and large associations were found between players initial MAS or VO2max (from r = 0.50; ± 0.17 to r = 0.56; ± 0.11 95% CL, p = 0.026 to 0.049) and RPEmus ML in 1-4 and 1-8 week periods. The current study suggests that a better cardiovascular capacity could be connected with a lower RPEres TL and higher RPEmus ML.

#2 Injury burden differs considerably between single teams from German professional male football (soccer): surveillance of three consecutive seasons
Reference: Knee Surg Sports Traumatol Arthrosc. 2019 Jul 19. doi: 10.1007/s00167-019-05623-y. [Epub ahead of print]
Authors: Klein C, Luig P, Henke T, Platen P
Summary: The purpose of this study was to analyse unique injury data of the national statutory accident insurance for the two highest divisions in German male football (Bundesliga and 2. Bundesliga) over three consecutive seasons regarding inter-season, inter-division and inter-team differences. This was a prospective observational open cohort study over the seasons 2014/2015, 2015/2016 and 2016/2017. Every acute injury that was registered by clubs or physicians with the German statutory accident insurance for professional athletes (VBG) as part of occupational accident reporting and that led to time loss and/or to medical attention, was included. The complete sample consisted of 1449 players. The study covered 2663.5 player seasons with an observed match exposure of 69,058 h and a projected training exposure of 529,136 h. In total, 7493 injuries were included. The overall incidence rate was 12.5 (± 0.28) injuries per 1000 exposure hours, which translated into match and training rates of 47.0 (± 1.62) and 8.02 (± 0.24) injuries per 1000 h, respectively. Findings of 2.7 injuries per player and season underline the need of effective preventive approaches. Higher injury incidences in seasons after international tournaments suggest an increasing risk of injury with increasing number of matches. However, large differences between the single teams from the same division indicate that a reduction in the injury burden is generally possible. Continuing the presented injury surveillance might be helpful to identify injury trends in the future and to evaluate the effectiveness of preventive approaches under real-life conditions.

#3 An Approach to the Fatigue in Young Soccer Players Resulting from Sided Games
Reference: Sports (Basel). 2019 Jul 18;7(7). pii: E174. doi: 10.3390/sports7070174.
Authors: Castillo D, Yanci J, Sánchez-Díaz S, Raya-González J
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Summary: It is crucial to understand the fatigue associated with sided games (SGs) of soccer in the training context, in order to establish the appropriate intervals between training sessions. Thus, the aim of this study was to investigate the effects of different SGs on internal load, measured by the session rating of perceived exertion (sRPE), and on sprint performance. Ten outfield players (age: 14.5 ± 0.5 years, height: 169 ± 6 cm, body mass: 59.7 ± 6.4 kg) belonging to U15 age category participated in this study. The participants played four SG formats with modifications in the pitch size and in the bout duration, but with the same total duration for the SGs (SG1, SG2, SG3, and SG4). All the players performed a 10 and a 30 m sprint test before and after the SGs. The internal load was measured by the sRPE. The results showed no significant differences (p > 0.05) in the sRPE registered by the soccer players for the different SGs, but worse sprint performances over the 10 m (p < 0.05; ES: 0.74-1.38, large) and 30 m (p < 0.05; ES: 0.70-2.10, moderate to large) distances after completion of the SGs, except the 10 m sprint after SG2 and SG3 (p > 0.05; ES: 0.43-0.55, moderate). In addition, no correlation (p > 0.05) was reported between the sprint performances for the 10 and 30 m distances and the sRPE registered during the SGs. These results could be useful for technical staff wishing to design the playing area and bout duration of their training tasks effectively.

#4 A Genome-Wide Association Study of Sprint Performance in Elite Youth Football Players
Reference: J Strength Cond Res. 2019 Jul 22. doi: 10.1519/JSC.0000000000003259. [Epub ahead of print]
Authors: Pickering C, Suraci B, Semenova EA, Boulygina EA, Kostryukova ES, Kulemin NA, Borisov OV, Khabibova SA, Larin AK, Pavlenko AV, Lyubaeva EV, Popov DV, Lysenko EA, `Vepkhvadze TF, Lednev EM, Leońska-Duniec A, Pająk B, Chycki J, Moska W, Lulińska-Kuklik E, Dornowski M, Maszczyk A, Bradley B, Kana-Ah A, Cięszczyk P, Generozov EV, Ahmetov II
Summary: Sprint speed is an important component of football performance, with teams often placing a high value on sprint and acceleration ability. The aim of this study was to undertake the first genome-wide association study to identify genetic variants associated with sprint test performance in elite youth football players and to further validate the obtained results in additional studies. Using micro-array data (600 K-1.14 M single nucleotide polymorphisms [SNPs]) of 1,206 subjects, we identified 12 SNPs with suggestive significance after passing replication criteria. The polymorphism rs55743914 located in the PTPRK gene was found as the most significant for 5-m sprint test (p = 7.7 × 10). Seven of the discovered SNPs were also associated with sprint test performance in a cohort of 126 Polish women, and 4 were associated with power athlete status in a cohort of 399 elite Russian athletes. Six SNPs were associated with muscle fiber type in a cohort of 96 Russian subjects. We also examined genotype distributions and possible associations for 16 SNPs previously linked with sprint performance. Four SNPs (AGT rs699, HSD17B14 rs7247312, IGF2 rs680, and IL6 rs1800795) were associated with sprint test performance in this cohort. In addition, the G alleles of 2 SNPs in ADRB2 (rs1042713 & rs1042714) were significantly over-represented in these players compared with British and European controls. These results suggest that there is a genetic influence on sprint test performance in footballers, and identifies some of the genetic variants that help explain this influence.

#5 Kinematic Profile of Visually Impaired Football Players During Specific Sports Actions
Reference: Sci Rep. 2019 Jul 23;9(1):10660. doi: 10.1038/s41598-019-47162-z.
Authors: Finocchietti S, Gori M, Souza Oliveira A
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Summary: Blind football, or Football 5-a-side, is a very popular sport amongst visually impaired individuals (VI) worldwide. However, little is known regarding the movement patterns these players perform in sports actions. Therefore, the aim of this study was to determine whether visually impaired players present changes in their movement patterns in specific functional tasks compared with sighted amateur football players. Six VI and eight sighted amateur football players performed two functional tasks: (1) 5 m shuttle test and (2) 60 s ball passing against a wall. The sighted players performed the tests while fully sighted (SIG) as well as blindfolded (BFO). During both tasks, full-body kinematics was recorded using an inertial motion capture system. The maximal center-of-mass speed and turning center-of-mass speed were computed during the 5 m shuttle test. Foot resultant speed, bilateral arm speed, and trunk flexion were measured during the 60 s ball passing test. The results showed that VI players achieved lower maximal and turning speed compared to SIG players (p < 0.05), but BFO were slower than the VI players. The VI players presented similar foot contact speed during passes when compared to SIG, but they presented greater arm movement speed (p < 0.05) compared to both SIG and BFO. In addition, VI players presented greater trunk flexion angles while passing when compared to both SIG and BFO (p < 0.05). It is concluded that VI players present slower speed while running and turning, and they adopt specific adaptations from arm movements and trunk flexion to perform passes.

#6 Interpersonal Dynamics in 2-vs-1 Contexts of Football: The Effects of Field Location and Player Roles
Reference: Front Psychol. 2019 Jul 3;10:1407. doi: 10.3389/fpsyg.2019.01407. eCollection 2019.
Authors: Laakso T, Davids K, Liukkonen J, Travassos B
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Summary: This study analyzed the spatial-temporal interactions that sustained 2-vs-1 contexts in football at different field locations near the goal. Fifteen male players (under 15 years, age 13.2 ± 1.03 years, years of practice 4.2 ± 1.10 years), 5 defenders, 7 midfielders, and 3 attackers, participated in the study. Each participant performed a game to simulate a 2-vs-1 sub-phase as a ball carrier, second attacker, and defender at three different field locations, resulting in a total number of 142 trials. The movements of participants in each trial were recorded and digitized with TACTO software. Values of interpersonal distance between the ball carrier and defender and interpersonal angles between players and between the goal target, defender, and ball carrier were calculated. The results revealed a general main effect of field location. Generally, the middle zone revealed the lowest values of interpersonal distance and angle between players and the right zone and the highest values of interpersonal distance between players and interpersonal angle between players and the goal. Related with participants' roles, defenders revealed subtle differences as attackers on interpersonal distances and relative angles compared with midfielders and attackers. Findings supported that field location is a key constraint of players' performance and that players' role constraint performance effectiveness in football.

#7 Characteristics of potential concussive events in three elite football tournaments
Reference: Inj Prev. 2019 Jul 22. pii: injuryprev-2019-043242. doi: 10.1136/injuryprev-2019-043242. [Epub ahead of print]
Authors: Armstrong N, Rotundo M, Aubrey J, Tarzi C, Cusimano MD
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Summary: Identify patterns in the nature and characteristics of potential concussive events (PCEs) in football. This study analysed the incidence and characteristics of PCEs that occurred during the 2014 and 2018 Fédération Internationale de Football Association World Cups, and the 2016 UEFA Euro Cup. PCEs were defined as direct head collision incidents resulting in the athlete being unable to immediately resume play for at least 5 sec following impact. A total of 218 incidents were identified in 179 matches (1.22 per match, 36.91 per 1000 hours of exposure). The most common mechanism of PCE was elbow-to-head (28.7%, n=68). The frontal region was the most frequently affected location of impact with 22.8% (n=54). Our study defined the identification, prevalence and nature of PCEs in professional international soccer tournaments. Our findings indicate the different contexts and mechanisms of head contact and contact to different regions of the head can be associated with varying signs of concussion. The results highlight targets for future injury prevention strategies.

#8 Neuromuscular changes in football players with previous hamstring injury
Reference: Clin Biomech (Bristol, Avon). 2019 Jul 13;69:115-119. doi: 10.1016/j.clinbiomech.2019.07.010. [Epub ahead of print]
Authors: Areia C, Barreira P, Montanha T, Oliveira J, Ribeiro F
Summary: Impact of prior injury on myoelectrical activity of the hamstrings during isokinetic eccentric contractions has received increased literature attention. This cross-sectional study aimed to assess neuromuscular adaptations, namely proprioception, core stability, muscle strength, extensibility and activity, in football players with history of hamstring strain injury. Seventeen players, 10 with history of hamstring injury and 7 without prior injury underwent isokinetic strength testing, eccentric knee extension at 30 and 120°/s. Myoelectrical activity of bicep femoris and medial hamstrings was calculated at 30, 50 and 100 ms after onset of contraction. Functional tests included core stability, muscle strength, and knee proprioception tests. Differences were observed between Hamstring Group injured and uninjured and Control Group dominant limbs in the bicep femoris activity at almost all times in both velocities (p < 0.05). Joint position sense error was higher in the injured side compared to uninjured and control dominant limb; additionally there were also differences between injured and uninjured limb in the triple-hop test. Previously injured side showed deficits in bicep femoris myoelectrical activity after onset of contraction during eccentric testing, proprioceptive deficits, and functional asymmetry.

#9 Effects of Different Training Interventions on the Recovery of Physical and Neuromuscular Performance After a Soccer Match
Reference: J Strength Cond Res. 2019 Jul 31. doi: 10.1519/JSC.0000000000003269. [Epub ahead of print]
Authors: Trecroci A, Porcelli S, Perri E, Pedrali M, Rasica L, Alberti G, Longo S, Iaia FM
Summary:  In competitive soccer, players are frequently required to play in periods with congested fixtures in which they have limited time to recover between matches (3-4 days). Thus, finding the most appropriate intervention strategy to limit players' neuromuscular (muscle function of lower limbs) and physical (running performance) impairments in this short period becomes crucial. The aim of the study was to examine how muscle function of knee extensors and flexors and sprint performance recovered +72 hours after match in relation to different field-based training sessions. Using a crossover design, 9 subelite players (age 17.6 ± 0.5 years, height 1.77 ± 0.02 m, body mass 66.4 ± 5.8 kg) underwent a soccer-specific training (SST) session or an active recovery regime (AR) on the second day after a match. Immediately after (0 hour) and +72 hours after match, 30-m sprint and repeated sprint ability (RSA) were assessed. Maximum isometric voluntary force (MVF) of knee extensors and flexors was determined at 120° and 90° (with 180° being full extension), respectively. SST and AR promoted similar effects on the recovery kinetics of sprint, RSA, and MVF of knee extensors (p > 0.05). However, compared with SST, AR promoted a significantly better restoration of MVF of knee flexors (p < 0.05) after +72 hours from the match. Because muscle fatigue has been related with increased hamstring injury risk, a training based on AR can be a valid intervention to promote the recovery of muscle force production of knee flexors and reduce hamstring injury risk in the postmatch period.

#10 Anterior Cruciate Ligament Repair in a Professional Soccer Player Using Internal Brace Ligament Augmentation: A Case Report Focusing on Rehabilitation
Reference: Surg Technol Int. 2019 Aug 1;35. pii: sti35/1162. [Epub ahead of print]
Authors: McIntyre V, Hopper GP, Mackay GM
Summary: Anterior cruciate ligament (ACL) reconstruction with hamstring or patellar tendon autograft has been the gold standard for the operative treatment of an ACL rupture for many years. Repair with Internal Brace Ligament Augmentation (IBLA) is a new technique that uses ultra-high strength tape (FiberTape, Arthrex, Naples, FL, USA) to bridge the ligament. This technique reinforces the ligament as a secondary stabiliser, encouraging natural healing of the ligament by protecting it during the healing phase and supporting early mobilisation. This retrospective case report focuses on the rehabilitation of a 21-year-old male professional soccer player who ruptured his ACL in a contact injury whilst playing a competitive game. He underwent ACL repair with IBLA two weeks following injury. The six-month rehabilitation programme consisted of gradual progressions for mobility, proprioception, strengthening, cardiovascular maintenance and running in conjunction with physiotherapy to assist with the maintenance of soft tissue quality, pain management and control of oedema. After completing the rehabilitation programme, the patient returned to unrestricted sporting activity within six months. At 18-month follow-up, the patient continues to play at the same competitive level without any issues. This rehabilitation programme after ACL repair with IBLA successfully enabled a professional soccer player to return to his pre-injury playing level.

#11 Posture correctness of young female soccer players
Reference: Sci Rep. 2019 Aug 1;9(1):11179. doi: 10.1038/s41598-019-47619-1.
Authors: Żuk B, Sutkowski M, Paśko S, Grudniewski T
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Summary: The objectives of the study were to evaluate the correctness of the body posture of female soccer players in the frontal plane from the back based on selected body points in two static positions (habitual and actively corrected) using a non-contact optical measurement method. Forty-two young women (aged 16-20) playing soccer in a sports club in Poland were examined and compared with controls. The spatial coordinates (x, y, z) of the selected body points were determined. Four points (OcL, OcR, PvL and PvR) were extracted and used to calculate vectors [Formula: see text] and [Formula: see text] for analysis. The results show that median of the pelvic line angle was positive (PvR was lower than PvL) in both groups. For the habitual posture, the absolute value of the difference between the 25th and 75th percentiles in the pelvic line was almost three times greater among the soccer players than the controls (ratio between soccer players and controls: 2.93). Static postural imbalances in female soccer players require diagnosis of the sacroiliac joints with analysis of lumbar-pelvic system support and inhibition in the context of myofascial connection integration. Exercises can be implemented to stabilize the lumbar-pelvis complex as prophylaxis for spinal overload during the training cycle.

#12 Comparison of Complex Versus Contrast Training on Steroid Hormones and Sports Performance in Male Soccer Players
Reference: J Chiropr Med. 2019 Jun;18(2):131-138. doi: 10.1016/j.jcm.2018.12.001. Epub 2019 Jun 26.
Authors: Ali K, Verma S, Ahmad I, Singla D, Saleem M, Hussain ME
Summary: The purpose of this study was to compare the effects of a complex versus a contrast training regimen with steroid hormones and the performance of soccer players. Thirty-six professional male soccer players were randomly divided into 3 equal groups: complex training (n = 12; body mass index [BMI], 22.95 ± 1.76 kg/m2), contrast training (n = 12; BMI, 22.05 ± 2.03 kg/m2), and control (n = 12; BMI, 22.27 ± 1.44 kg/m2). Players from the complex and contrast groups were trained for 6 weeks (3 d/wk). The complex group performed 4 different exercises, each composed of strength (80% of 1 repetition maximum [RM]) and power components alternately. The contrast group performed the same strengthening exercises alternately at different intensities (40% and 80% of 1 RM). All players were tested for free testosterone, cortisol, vertical jump, 20-m sprint, and agility T-test at the baseline and after 6 weeks of training. A 3 × 2 mixed analysis of variance revealed a significant difference in time effect (P ≤ .05), whereas a nonsignificant difference was found in the group effect for all outcome variables. group × time interaction was significant in all the variables (P < .01) except cortisol (P = .28). Complex training showed greater improvement in physical performance and free testosterone concentration compared with contrast training, whereas both types of training decreased cortisol concentration in a similar fashion.





Latest research in football - week 29 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:


#1 A new approach to study the relative age effect with the use of additive logistic regression models: A case of study of FIFA football tournaments (1908-2012)
Reference: PLoS One. 2019 Jul 16;14(7):e0219757. doi: 10.1371/journal.pone.0219757. eCollection 2019.
Authors: Saavedra-García M, Matabuena M, Montero-Seoane A, Fernández-Romero JJ
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Summary: The relative age effect plays an important role in the pursuit of excellence, providing advantage to athletes born at the beginning of the year or near the cut-off date. This phenomenon has been observed in areas such as sports, education or business. Traditionally, the chi-square test has been used to analyze whether there are statistically significant differences in the distribution of births in each of the four quarters of the year. However, this approach is limited, focusing only on the analysis of the response variable, without taking into account the effect of a set of predictive variables. In this paper a new approach is proposed to study the relative age effect with the use of a logistic regression additive model. The new method has been evaluated with a sample of 21,639 players involved in football tournaments organized by the Fédération Internationale de Football Association (FIFA) between 1908 and 2012. New conclusions have been established that the relative age effect exists regarding player age and the year of the competition in male FIFA competitions and its effect is dynamic and complex.

#2 Effect of a New Rule Limiting Full Contact Practice on the Incidence of Sport-Related Concussion in High School Football Players
Reference: Am J Sports Med. 2019 Jul 15:363546519860120. doi: 10.1177/0363546519860120. [Epub ahead of print]
Authors: Pfaller AY, Brooks MA, Hetzel S, McGuine TA
Summary: Sport-related concussion (SRC) has been associated with cognitive impairment, depression, and chronic traumatic encephalopathy. American football is the most popular sport among males in the United States and has one of the highest concussion rates among high school sports. Measured head impacts and concussions are approximately 4 times more common in contact practices compared with noncontact practices. The Wisconsin Interscholastic Athletic Association passed new rules defining and limiting contact during practice before the 2014 football season. The purpose was to determine if the SRC rate is lower after a rule change that limited the amount and duration of full-contact activities during high school football practice sessions. A total of 2081 high school football athletes enrolled and participated in the study in 2012-2013 (before the rule change), and 945 players participated in the study in 2014 (after the rule change). Players self-reported previous concussion and demographic information. Athletic trainers recorded athlete exposures (AEs), concussion incidence, and days lost for each SRC. Chi-square tests were used to compare the incidence of SRC in prerule 2012-2013 seasons with the incidence in the postrule 2014 season. Wilcoxon rank sum tests were used to determine differences in days lost because of SRC. A total of 67 players (7.1%) sustained 70 SRCs in 2014. The overall rate of SRC per 1000 AEs was 1.28 in 2014 as compared with 1.58 in 2012-2013 (P = .139). The rate of SRC sustained overall in practice was significantly lower (P = .003) after the rule change in 2014 (15 SRCs, 0.33 per 1000 AEs) as compared with prerule 2012-2013 (86 SRCs, 0.76 per 1000 AEs). There was no difference (P = .999) in the rate of SRC sustained in games before (5.81 per 1000 AEs) and after (5.74 per 1000 AEs) the rule change. There was no difference (P = .967) in days lost from SRC before (13 days lost [interquartile range, 10-18]) and after (14 days lost [interquartile range, 10-16]) the rule change. The rate of SRC sustained in high school football practice decreased by 57% after a rule change limiting the amount and duration of full-contact activities, with no change in competition concussion rate. Limitations on contact during high school football practice may be one effective measure to reduce the incidence of SRC.

#3 Influence of pitch size and age category on the physical and physiological responses of young football players during small-sided games using GPS devices
Reference: Res Sports Med. 2019 Jul 15:1-11. doi: 10.1080/15438627.2019.1643349. [Epub ahead of print]
Authors: Lemes JC, Luchesi M, Diniz LBF, Bredt SDGT, Chagas MH, Praça GM
Summary: This study aimed to compare the physical and physiological responses of young football players of different categories during small-sided games (SSGs) played on different pitch sizes. Forty-eight (24 U-13 and 24 U-14) athletes played a 3 vs. 3 + 1 SSG in two experimental conditions: regular (36 × 27 m) and large pitch sizes (40 × 29 m). The total distance covered, the distances covered at different speed zones (0 to 6.9 km/h, 6.9 to 14.3, and 14.3 to 21.4), maximum heart rate, and mean heart rate were recorded. The results showed that older athletes covered larger distances during SSGs (p = 0.001; d = 0.937; large effect) and lower distances at the lowest (0-6.9 km/h) speed zone (p = 0.001; d = 0.657; moderate-to-large effect). Neither the physical nor physiological variables (except for distance covered between 14.3 and 21.4 km/h) differed between pitch sizes. This result indicates that pitch size may not impact the physical or physiological responses of U-13 and U-14 players during SSGs, but differences between categories were found. In conclusion, the development of tactical skills may be desirable to better explore the available space in the same age categories.

#4 Comparative study on skill and health related physical fitness characteristics between national basketball and football players in Sri Lanka
Reference: BMC Res Notes. 2019 Jul 12;12(1):397. doi: 10.1186/s13104-019-4434-6.
Authors: Kariyawasam A, Ariyasinghe A, Rajaratnam A, Subasinghe P
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Summary: The purpose was to compare health and skill related physical fitness profiles between healthy, male, basketball and football players of Sri Lankan national teams. Thirty basketball players (mean age 24 ± 4.5 years) and 30 football players (mean age 23 ± 4.3 years) were evaluated for health related fitness characteristics (body fat percentage, cardio-respiratory fitness, isometric hand grip strength, lower body and upper body muscular strength, abdominal and upper body muscular endurance, and flexibility) and skill related fitness characteristics (agility, speed, explosive throwing power, jumping power, reaction time, coordination, static balance). Fat percentage, upper body endurance, grip strength, running speed, explosive power, jumping power, balance and coordination were significantly higher in basketball players than in footballers. Football players had better upper body strength, flexibility, reaction time and agility than those of basketball players. The latter two were statistically significant. Basketball players had better mean lower body strength, although not significant. Fitness characteristics were different between basketball and football players. The results have implications in tailoring training activities to improve relevant fitness characteristics.

#5 Effects of a six-week period of congested match play on plasma volume variations, hematological parameters, training workload and physical fitness in elite soccer players
Reference: PLoS One. 2019 Jul 25;14(7):e0219692. doi: 10.1371/journal.pone.0219692. eCollection 2019.
Authors: Saidi K, Zouhal H, Rhibi F, Tijani JM, Boullosa D, Chebbi A, Hackney AC, Granacher U, Bideau B, Ben Abderrahman A
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Summary: The aims of this study were to investigate the effects of a six-week in-season period of soccer training and games (congested period) on plasma volume variations (PV), hematological parameters, and physical fitness in elite players. In addition, we analyzed relationships between training load, hematological parameters and players' physical fitness. Eighteen elite players were evaluated before (T1) and after (T2) a six-week in-season period interspersed with 10 soccer matches. At T1 and T2, players performed the Yo-Yo intermittent recovery test level 1 (YYIR1), the repeated shuttle sprint ability test (RSSA), the countermovement jump test (CMJ), and the squat jump test (SJ). In addition, PV and hematological parameters (erythrocytes [M/mm3], hematocrit [%], hemoglobin [g/dl], mean corpuscular volume [fl], mean corpuscular hemoglobin content [pg], and mean hemoglobin concentration [%]) were assessed. Daily ratings of perceived exertion (RPE) were monitored in order to quantify the internal training load. From T1 to T2, significant performance declines were found for the YYIR1 (p<0.001, effect size [ES] = 0.5), RSSA (p<0.01, ES = 0.6) and SJ tests (p< 0.046, ES = 0.7). However, no significant changes were found for the CMJ (p = 0.86, ES = 0.1). Post-exercise, RSSA blood lactate (p<0.012, ES = 0.2) and PV (p<0.01, ES = 0.7) increased significantly from T1 to T2. A significant decrease was found from T1 to T2 for the erythrocyte value (p<0.002, ES = 0.5) and the hemoglobin concentration (p<0.018, ES = 0.8). The hematocrit percentage rate was also significantly lower (p<0.001, ES = 0.6) at T2. The mean corpuscular volume, mean corpuscular hemoglobin content and the mean hemoglobin content values were not statistically different from T1 to T2. No significant relationships were detected between training load parameters and percentage changes of hematological parameters. However, a significant relationship was observed between training load and changes in RSSA performance (r = -0.60; p<0.003). An intensive period of "congested match play" over 6 weeks significantly compromised players' physical fitness. These changes were not related to hematological parameters, even though significant alterations were detected for selected measures.

#6 Effects of an 8-Week Pre-seasonal Training on the Aerobic Fitness of Professional Soccer Players
Reference: J Strength Cond Res. 2019 Jul 19. doi: 10.1519/JSC.0000000000003209. [Epub ahead of print]
Authors: Michaelides MA, Parpa KM, Zacharia AI.
Summary: Pre-season in soccer training develops the physical requisites for competition and usually consists of a high volume of aerobic and anaerobic conditioning training including friendly games. The purpose of the study was to determine the effects of pre-season training on the aerobic fitness of professional soccer players. Nineteen professional male soccer players (age = 27.37 ± 3.67 years, height = 179.61 ± 5.17 cm, and body fat percentage = 11.3 ± 3.19%) participated in this study performed an incremental cardiopulmonary exercise testing on a treadmill before and after the 8 weeks of pre-season preparation. The results were analyzed using paired t tests, revealing significant differences on several indices. The subjects improved significantly on maximal aerobic capacity (V[Combining Dot Above]O2max) and lasted significantly longer on the treadmill (p < 0.05). The V[Combining Dot Above]O2 at ventilatory threshold (VT) and respiratory compensation point (RCP) increased significantly (p < 0.05). The running velocity at ventilatory thresholds (vVT and vRCP) and at V[Combining Dot Above]O2 max (vVO2max) also increased significantly (p < 0.05). In conclusion, the results of this study, as expected, demonstrated that the proposed 8 weeks of pre-season training program was sufficient to cause significant improvements on the aerobic performance indices of professional soccer players. The study confirms the beneficial changes in the process of adaptations that occur with this type of training and can assist coaches and trainers in planning a successful pre-season training program.

#7 In-season in-field variable resistance training: effects on strength, power, and anthropometry of junior soccer players
Reference: J Sports Med Phys Fitness. 2019 Jul 24. doi: 10.23736/S0022-4707.19.09937-7. [Epub ahead of print]
Authors: Izadi M, Arazi H, Ramirez-Campillo R, Mirzaei M, Saidei P
Summary: Soccer players' leg muscular strength and power have been shown to be significant due to their association with soccer-specific performance including jumps, sprints, tackles and kicks. The aim of this study, therefore, was to examine the effects of an in-season in- field variable resistance training (VRT) program on strength, power, and anthropometry of junior soccer players. A team of male soccer players were randomly divided into Experimental (n=10) and Control groups (n=10). The Control group performed 8 weeks of soccer training alone. The Experimental group performed squat VRT using chains in addition to soccer training. Measures before and after training included one repetition maximum (1RM) of squat, countermovement jump (CMJ), and anthropometric estimation of thigh muscle cross sectional area (CSA). The VRT induced large improvements in absolute (34.45%; p=0.001; Cohen's d=1.78) and relative strength to thigh muscle CSA (21.53%; p=0.002; Cohen's d=1.04). Similarly, there were large (18.07%, p=0.007; Cohen's d=1.5) increases in jump height and medium gains in absolute peak power output (16.13%; p=0.009; Cohen's d=0.34) and relative peak power output to thigh muscle CSA (9.6%; p=0.002; Cohen's d=0.31). Further, there was a medium increase (5.9%, p=0.03; Cohen's d=0.36) in thigh muscle CSA. No significant changes were observed in the Control group. In-season in-field biweekly squat VRT enhanced strength and power measures in junior soccer players.

#8 Selection and promotion processes are not associated by the relative age effect in an elite Spanish soccer academy
Reference: PLoS One. 2019 Jul 24;14(7):e0219945. doi: 10.1371/journal.pone.0219945. eCollection 2019.
Auhors: Castillo D, Pérez-González B, Raya-González J, Fernández-Luna Á, Burillo P, Lago-Rodríguez Á
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Summary: The aim of this study was to analyze the influence of the relative age effect (RAE) on the selection and promotion processes in an elite soccer academy. One hundred and eleven elite youth players who belonged to an elite soccer club from the Spanish "La Liga" participated in this study. Players were classified into three age-categories: under 14 years (U14), under 16 years (U16) and under 18 years (U18); and they were also classified in quartiles based on their date of birth (i.e., January-March, Q1; April-June, Q2; July-September, Q3; October-December, Q4). In addition, two further classification criteria were established based on the selection (i.e., selected and non-selected players) and promotion (i.e., promoted and non-promoted players) processes. The main results showed that in U14 and U16 age-categories, players born early in the year were over-represented compared to players born late in the year, although birth-distribution was not associated with the likelihood of a player to be selected or promoted. In addition, less fat in sum skinfolds, less percentage of fat, higher percentage of muscle and lower endomorphy and mesomorphy components were showed in U14 selected players, in comparison with non-selected players. Likewise, better sprint performance was found in U16 selected players versus non-selected ones. However, no significant differences on anthropometry, body composition, somatotype and physical performance were found between promoted and non-promoted players. Therefore, our results suggest there is need for coaches to reorient their talent identification programs in order to make sure that players selected to continue playing in the club have the potential to promote to the excellence in soccer.

#9 Changing Rules and Configurations During Soccer Small-Sided and Conditioned Games. How Does It Impact Teams' Tactical Behavior?
Reference: Front Psychol. 2019 Jul 9;10:1554. doi: 10.3389/fpsyg.2019.01554. eCollection 2019.
Authors: Machado JC, Ribeiro J, Palheta CE, Alcântara C, Barreira D, Guilherme J, Garganta J, Scaglia AJ
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Summary: The present study aimed to investigate how team's tactical behavior varies within and between age categories in different Small-Sided and Conditioned Games' configurations and conditions. Twenty non-elite youth male soccer players (U15, n = 10, mean age = 13.5 ± 1.2 years; U17, n = 10, mean age = 16.3 ± 0.5 years) were selected. Thirty-six Small-Sided and Conditioned Games (SSCG) were played in both categories, namely three Representative SSCG (R-SSCG), three Maintaining Ball Possession Games (MBPG) and three Progression to Target Games (PTG) performed for each configuration (Gk+3vs3+Gk and Gk+4vs4+Gk). Teams' tactical behavior was analyzed based on simple and composite performance indicators, as well as through Lag Sequential Analysis. Rules manipulation and SSCG configurations influenced teams' tactical behavior on both categories, but in different ways. Teams composed by younger players presented greater difficulties in MBPG played in smaller games configuration, while Gk+4vs4+Gk configuration can be used to enhance teams' tactical performance of younger players in R-SSCG and MBPG conditions. Moreover, increasing rules manipulations appeared to negatively impact on teams' exploratory behavior. Therefore, practitioners should carefully manipulate key constraints to adapt task demands to players' age category and training session's goals in order to enhance tactical performance.

#10 Differences in Player Position Running Velocity at Lactate Thresholds Among Male Professional German Soccer Players
Reference: Front Physiol. 2019 Jul 9;10:886. doi: 10.3389/fphys.2019.00886. eCollection 2019.
Authors: Schwesig R, Schulze S, Reinhardt L, Laudner KG, Delank KS, Hermassi S
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Summary: This study investigated the differences in running velocities at specific lactate thresholds among male German soccer players. One hundred fifty-two professional (3rd league: n = 78; 4th league: n = 74) male soccer players (mean ± SD; age: 24.7 ± 4.37 years, body mass: 80.8 ± 7.33 kg, body height: 1.83 ± 0.06 m) volunteered for the investigation. Players were categorized as goalkeepers, central defenders, central midfielders, wings and forward. Players completed a treadmill test, at incremental speeds, to determine running velocity at different blood lactate concentrations (v2 = 2 mmol/l; v4 = 4 mmol/l; and v6 = 6 mmol/l). In addition, the largest difference between positions for running velocity was found at the lactate threshold v2 (p = 0.005). The running data revealed that only goalkeepers had significantly lower velocities at the lactate thresholds compared to outfield players. The central midfielders showed the highest average performance level at the lactate thresholds (v2: 12.5 ± 1.20 km/h; v4: 15.2 ± 1.14 km/h; and v6: 16.6 ± 1.14 km/h). In conclusion, this study provides soccer and position-specific reference data for the running performance of male professional German soccer players to evaluate the endurance performance in a standardized way. In this context, future research should extend the database for the first and second leagues. Further research assessing running performance during competition matches over the entire season is required to validate the endurance test performance data.

#11 Salivary Metabolome and Soccer Match: Challenges for Understanding Exercise induced Changes
Reference: Metabolites. 2019 Jul 11;9(7). pii: E141. doi: 10.3390/metabo9070141.
Authors: Pitti E, Petrella G, Di Marino S, Summa V, Perrone M, D'Ottavio S, Bernardini A, Cicero DO
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Summary: Saliva samples of seventeen soccer players were analyzed by nuclear magnetic resonance before and after an official match. Two different ways of normalizing data are discussed, using total proteins and total metabolite concentrations. Changes in markers related to energy, hydration status, amino acids and other compounds were found. The limits and advantages of using saliva to define the systemic responses to exercise are examined, both in terms of data normalization and interpretation, and the time that the effect lasts in this biofluid, which is shorter to that commonly observed in blood. The heterogeneous nature and different timing of the exercise developed by players also plays an important role in the metabolic changes that can be measured. Our work focuses mainly on three different aspects: The effect that time sampling has on the observed effect, the type of normalization that is necessary to perform in order to cope with changes in water content, and the metabolic response that can be observed using saliva.

#12 The Importance of Fundamental Motor Skills in Identifying Differences in Performance Levels of U10 Soccer Players
Reference: Sports (Basel). 2019 Jul 22;7(7). pii: E178. doi: 10.3390/sports7070178.
Authors: Jukic I, Prnjak K, Zoellner A, Tufano JJ, Sekulic D, Salaj S
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Summary: This study examined the differences in fundamental motor skills (FMSs) and specific conditioning capacities (SCCs) between a coach's classification of first team (FT) and second team (ST) U10 soccer players and examined the most important qualities based on how the coach differentiates them. The FT (n = 12; Mage = 9.72 ± 0.41) and ST (n = 11; Mage = 9.57 ± 0.41) soccer players were assessed using the Test of Gross Motor Development-2, standing long jump, sit and reach, diverse sprints, and the 20 m multistage fitness test (MSFT). The coach's subjective evaluation of players was obtained using a questionnaire. No significant differences existed between the FT and ST in any variables (p > 0.05). However, large and moderate effect sizes were present in favour of the FT group in locomotor skills (d = 0.82 (0.08, 1.51)), gross motor quotient (d = 0.73 (0.00, 1.41)), height (d = 0.61 (-0.12, 1.29)), MSFT (d = 0.58 (-0.14, 1.25)), and maximum oxygen uptake (VO2max) (d = 0.55 (-0.17, 1.22)). Furthermore, the coach perceived the FT group as having greater technical and tactical qualities relative to ST players. This suggests that it might be more relevant for players of this age to develop good FMS connected to technical skills, before focusing on SCC. Therefore, it might be beneficial for soccer coaches to emphasize the development of FMSs due to their potential to identify talented young soccer players and because they underpin the technical soccer skills that are required for future soccer success.





Latest research in football - week 28 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Biomarkers of insulin action during single soccer sessions before and after a 12-week training period in type 2 diabetes patients on a caloric-restricted diet
Reference: Physiol Behav. 2019 Jul 16:112618. doi: 10.1016/j.physbeh.2019.112618. [Epub ahead of print]
Authors: de Sousa MV, Fukui R, Dagogo-Jack S, Krustrup P, Zouhal H, da Silva MER
Summary: We investigated the biomarkers of insulin action as well as changes in free fatty acids and lactate concentration after an acute soccer session pre and post training with caloric-restricted diet versus diet alone in type 2 diabetes (T2D) patients. Fifty-one middle-aged (61.1 ± 6.4 years) T2D patients were randomly allocated to the soccer+diet group (SDG) or the diet group (DG). The control group comprised T2D patients observing a caloric-restricted diet who did not receive soccer training. Over 12 weeks, SDG performed 3 × 40 min per week of soccer training. The first soccer session for SDG induced acute increases in blood lactate (1.4 ± 0.1-6.0 ± 0.7 mmol/L, P < 0.05) and glucagon levels (112.1 ± 6.2-142.9 ± 8.0 pg/mL, P < 0.05), whereas glucose and insulin levels remained unchanged. Moreover, this session showed suppressed insulin levels as well as higher free fatty acids, lactate levels and glucagon/insulin ratio compared to DG (p < 0.05). After 12 weeks, a baseline decrease was observed in glucagon, leptin and lactate levels in SDG and DG (p < 0.05), whereas HOMA-IR, Adipo-IR and glucose levels were lower only in SDG (p < 0.05). At the last soccer training session, the blood lactate response was significantly lower than for the first session (4.0 ± 0.4 vs 6.0 ± 0.7 mmol/L). At 48 h pre intervention, a decrease was observed in leptin levels (p < 0.05), which remained lower post intervention. The positive correlation between leptin and insulin, and the lower levels after training, could be attributed to the improved insulin sensitivity along with the weight loss observed in both groups (~3.4 kg for DG and 3.7 kg for SDG). Acute soccer sessions markedly improved insulin action markers in T2D patients, while the cumulative effects enhanced insulin sensitivity and decreased risk factors associated with cardiovascular disease after 12 weeks of intervention better than caloric-restricted diet.

#2 "REOFUT" as an Observation Tool for Tactical Analysis on Offensive Performance in Soccer: Mixed Method Perspective
Reference: Front Psychol. 2019 Jun 28;10:1476. doi: 10.3389/fpsyg.2019.01476. eCollection 2019.
Authors: Aranda R, González-Ródenas J, López-Bondia I, Aranda-Malavés R, Tudela-Desantes A, Anguera MT
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Summary: Performance analysis in complex sports like soccer requires the study of the influence of the interaction between both teams during the game on final performance. The mixed methods approach involves the collection, analysis, and interpretation of qualitative and quantitative data for the same purpose and within the framework of the same study. To build certain observation tools, mixed methods are necessary in order to take advantage of integration between qualitative and quantitative elements. The aim of this study was to develop a new no standard observation tool to analyze soccer offensive performance considering not only the observed team but also some aspects of the opponent behavior, as well as to test its reliability. The process consisted in expert meetings and exploratory observations. Experts carried out several design and re-design steps of the observation tool to its final form which includes two macro-criteria and 31 dimensions. The basic unit of analysis was the "team possession" and the main aims of study were: (a) technical, tactical and spatial characteristics of the start, the development and the end of the team possession and its offensive performance, (b) the behavior of the observed team just after losing the ball possession and its defensive performance. Inter-observer and intra-observer analysis were carried out and kappa coefficient was calculated to test the observation tool reliability and improve the quality of data. Results indicate that optimal inter and intra-reliability levels obtained in this work are high enough as for suggesting that the observation tool for offensive performance in soccer (REOFUT) could be an adequate tool for analyzing offensive play actions and their performance in soccer.

#3 Self-Control in Aiming Supports Coping With Psychological Pressure in Soccer Penalty Kicks
Reference: Front Psychol. 2019 Jun 27;10:1438. doi: 10.3389/fpsyg.2019.01438. eCollection 2019.
Authors: Navia JA, van der Kamp J, Avilés C, Aceituno J
Summary: This study addressed the question whether coaches better allow athletes to self-control their decisions when under pressure or whether to impose a decision upon them. To this end, an experiment was conducted that manipulated the soccer kickers' degree of control in decision-making. Two groups of elite under-19 soccer players (n = 18) took penalty kicks in a self-controlled (i.e., kickers themselves decided to which side to direct the ball) and an externally controlled condition (i.e., the decision to which side to direct the ball was imposed upon the kickers). One group performed the penalty kick under psychological pressure (i.e., the present coaching staff assessed their performance), while the second group performed without pressure. Just before and after performing the kicks, CSAI-2 was used to measure cognitive and somatic anxiety and self-confidence. Further, the number of goals scored, ball placement and speed, and the duration of preparatory and performatory behaviors were determined. The results verified increased levels of cognitive and somatic anxiety after performing the kicks in the pressured group compared to the no-pressure group. In addition, degree of self-control affected the participants' performance, particularly in the pressured group. They scored more goals and placed the kicks higher in the self-controlled than in the externally-controlled condition. Participants also took more time preparing and performing the run-up in the self-controlled condition. Findings indicate that increased self-control helps coping with the debilitating effects of pressure and can counter performance deteriorations. The findings are discussed within the framework of self-control theories, and recommendations for practitioners and athletes are made.

#4 Variation of aerobic performance indices of professional elite soccer players during the annual macrocycle
Reference: J Sports Med Phys Fitness. 2019 Jul 15. doi: 10.23736/S0022-4707.19.09800-1. [Epub ahead of print]
Authors: Bekris E, Mylonis E, Gissis I, Katis A, Metaxas T, Komsis S, Kombotieta N
Summary: The purpose of the present study was to examine the variation of aerobic performance parameters of elite Greek soccer players. In the study participated twenty-four (24) male professional soccer players (age: 24.3±4.3 years, height: 180.3±3.8 cm and mass: 77.4±6.1 kg), who competed at the top level of the Greek National Championship. Four measurements regarding aerobic parameters were conducted during the annual training cycle (preseason, start of the season, end of the first championship round and end of the season). The ANOVA analysis showed that maximum oxygen uptake (VO2max) was significantly increased after the completion of the preseason and continued to increase until the end of the first round of the Championship. In contrast, a decline was observed towards the end of the season. The velocity to maximum oxygen uptake (vVO2max) and the velocity parameter in respiratory threshold were significantly increased at the end of the preseason and the end of the first round, while the parameters were differentiated at the end of the season. The lactate concentration showed no significant changes during the four measurements. A systematic observation of players' performance, especially recording parameters such as VO2max, during the annual training cycle, could provide the necessary feedback for both trainers and players in order to increase team performance.

#5 Knee isokinetic muscle strength and balance ratio in female soccer players of different age groups: a cross-sectional study
Reference: Phys Sportsmed. 2019 Jul 16. doi: 10.1080/00913847.2019.1642808. [Epub ahead of print]
Authors: Vargas VZ, Motta C, Peres B, Vancini RL, Andre Barbosa de Lira C, Andrade MS
Summary: As a consequence of years of soccer training and sexual maturation, there is an increase in lower body muscle mass and strength especially in the knee extensors and flexors muscles. In this context, the lack of knee joint stability, resulting from strength imbalance between knee extensor and flexors muscles, has been associated with knee injuries. The aim of this study was to compare the knee flexor and extensor muscle peak torque, average power, contralateral deficit, conventional and functional balance ratios of female soccer players from different age groups.  Sixty-six female soccer players were divided into four groups: under 13 (U13), under 15 (U15), under 17 (U17) years old and professional (PRO). Flexor and extensor knee muscle strength in concentric and eccentric actions of both limbs were assessed using isokinetic dynamometer. For the dominant limb, the knee concentric extensor muscles peak torques, assessed at 60 and at 240 deg/sec, and average power of U15 group were significantly higher than U13 group. Extensor muscles average power of PRO group was higher than U17. Dominant knee flexor average power of U15 was significant higher than U13 group. Peak torque at 60 deg/sec and 240 deg/sec and average power of PRO group were higher than U17 group. No differences were found regarding the eccentric action for flexor and extensor muscles. Conventional and functional balance ratios were similar among all age group, except for U13, which presented higher values than U15 group for dominant limb. The greatest increases in muscular performance occur when the athlete starts practicing soccer (after U13) and when they become professional (after U17) and the balance ratios, and muscle balance ratios remain stable in all age groups, although they are below the recommended level in the literature, which may increase the risk for lower limb injury

#6 The influence of youth soccer players' sprint performance on the different sided games' external load using GPS devices
Reference: Res Sports Med. 2019 Jul 15:1-12. doi: 10.1080/15438627.2019.1643726. [Epub ahead of print]
Authors: Castillo D, Raya-González J, Manuel Clemente F, Yanci J
Summary: The aims of this study are 1) to compare sided games' (SGs) external responses encountered by players according to pitch size and to 2) examine the relationships between sprint performance and SGs' external physical responses. Twenty soccer players under 15 years of age (U-15) participated in this study. Each player performed a sprinting test (10 m and 30 m sprints) and played a SG on two different pitch sizes (small at 100 [SSG] and large at 200 [LSG] m2 per player). Higher external responses (p < 0.01, ES = -6.41-1.22) were found in LSG in comparison to SSG, except to distance accelerating and decelerating (p > 0.05, ES = -0.26-0.27). Players who were faster over 10 and 30 m covered higher distances cruising and sprinting (r = -0.47/-0.66; ± 0.23/± 0.30, respectively, p < 0.05), performed a greater number of sprints, achieved higher maximum velocity (Velmax) during LSG and covered a greater distance at high-intensity accelerating (r = -0.50/-0.70; ±0.21/±0.29, respectively, p < 0.05) during both SG. LSG demanded a higher external load in comparison with SSG. In addition, the improved sprint capacity could allow players to perform greater running activities and short-term actions at high-intensities during SG.

#7 Injury Surveillance in Major League Soccer: A 4-Year Comparison of Injury on Natural Grass Versus Artificial Turf Field
Reference: Am J Sports Med. 2019 Jul 15:363546519860522. doi: 10.1177/0363546519860522. [Epub ahead of print]
Authors: Calloway SP, Hardin DM, Crawford MD, Hardin JM, Lemak LJ, Giza E, Forsythe B, Lu Y, Patel BH, Osbahr DC, Gerhardt MB, Mandelbaum BR, Baldwin WW
Summary: Artificial playing surfaces are becoming more common due to decreased cost of maintenance and increased field usability across different environmental conditions. The Fédération Internationale de Football Association (FIFA) has approved newer generation artificial turf for soccer competition at the elite level, but many elite-level athletes prefer to play on natural grass surfaces due to a perceived increase in injury rate, discomfort, and fatigability on artificial turf. Injury rates and rates of individually categorized types of injury experienced on artificial turf are noninferior to rates of injury on the standard comparator, natural grass, in elite-level Major League Soccer athletes. Over the course of 4 Major League Soccer seasons (2013-2016), athlete injury data were recorded electronically. Injury data recorded in matches between 2 Major League Soccer teams were then analyzed. Playing surface was known for each venue, and all artificial turf surfaces were rated as 2-star according to FIFA criteria. Incidence rate ratios (Artificial Turf ÷ Natural Grass) were calculated with a 95% CI (α = .05) for both overall injury incidence and individual injury subgroups. A noninferiority margin (δ) of 0.15 was used to determine noninferiority of injury incidence rates. A total of 2174 in-game injuries were recorded during the study period, with 1.54 injuries per game on artificial turf and 1.49 injuries per game on natural grass (incidence rate ratio, 1.033; 95% CI, 0.937-1.139). Within injury subgroups, overall ankle injury, Achilles injury, and ankle fracture were found to have a statistically higher incidence on artificial turf. Artificial turf was found to be noninferior to natural grass for overall foot injury and forefoot injury. No statistically significant differences were found in knee injuries between the 2 surfaces. The overall rate of injury on artificial turf was noninferior to that on natural grass. Within individual injury categories, a higher rate of ankle injury was found on artificial turf. No other injury subgroup demonstrated statistically significant differences between surfaces. FIFA 2-star rated artificial turf is a viable alternative to natural grass in elite-level soccer competition. Innovative research methods for comparing artificial turf versus natural grass may elucidate relative advantages with respect to player safety.

#8 Orthopedic injuries in a formation of a soccer club
Reference: Rev Bras Ortop. 2013 Jun 11;48(1):41-45. doi: 10.1016/j.rboe.2011.12.001. eCollection 2013 Jan-Feb.
Authors: Carvalho DA
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Summary: Football is one of the most popular sports in the world with approximately 400 million practitioners. All physical activity generates an overload somewhere in the locomotor system, above all, in young athletes. The purpose was to conduct the epidemiological survey of orthopedic injuries in a medical department of the categories of junior soccer a football club in Curitiba. Epidemiological survey of injuries in 310 different athletes during the 2009 and 2010 seasons were analysed. The number of recorded visits was 3.64 per athlete orthopedic complaints in two years. Furthermore, we find 2.88 injuries/1,000 hours of play, and the junior (under 20 and under 18) with the highest rate (3.05). The most frequent injury was contusion (32.15%), lower limbs, especially the thigh (3.94%). The higher incidence of injuries occurred in the Middle - campers (30.65%), being the training responsible for 88.31% of the complaints. The epidemiological survey of medical care is a medical department is an important tool for analysis of the main complaints, as well as the primary means of prevention and maintaining the health of athletes.

#9 Concussion in American Versus European Professional Soccer: A Decade-Long Comparative Analysis of Incidence, Return to Play, Performance, and Longevity
Reference: Am J Sports Med. 2019 Jul 15:363546519859542. doi: 10.1177/0363546519859542. [Epub ahead of print]
Authors: Ramkumar PN, Navarro SM, Haeberle HS, Luu BC, Jang A, Frangiamore SJ, Farrow LD, Schickendantz MS, Williams RJ 3rd
Summary: The incidence and effect of sports-related concussions (SRCs) within the global sport of professional soccer is poorly described. The purpose was to comparatively examine the effects of SRC on athletes in Major League Soccer (MLS) and the English Premier League (EPL) in terms of incidence, return to play (RTP), performance, and career longevity. Contracts, transactions, injury reports, and performance statistics from 2008 to 2017 were obtained and cross-referenced across 6 publicly available websites detailing MLS and EPL data, including official league publications. For each league, players who sustained a concussion were compared with the 2008-2017 uninjured player pool. RTP and games missed were analyzed and compared. Career length was analyzed with Kaplan-Meier survival curves. Player performance changes were evaluated before and after concussion. Of the 1784 eligible MLS and 2001 eligible EPL players evaluated over the 10-year period, the incidence of publicly reported concussions per 1000 athlete-exposures was 20.22 and 18.68, respectively (P = .53). The incidence of reported concussions steadily increased in both leagues. MLS players missed a mean 7.3 games after concussion (37.0 days missed); EPL players missed a mean 0.6 games after concussion (10.9 days missed) (P < .0001, P < .0001). Statistical performance in terms of games started, assists, shots on goal, and total shots after concussion was significantly reduced at all nongoalie positions for players in the EPL; however, MLS nongoalie positions with concussion had no significant decreases in these categories. Goalies in both leagues had no significant change in performance or games started. The probability of playing a full season after concussion was not significantly decreased when compared with the uninjured pool in both leagues. This study established the SRC incidence among elite soccer players in 2 international professional leagues and identified major RTP and performance differences between EPL and MLS players. While career longevity was unaffected, the approach to managing concussion as in MLS may better promote player safety and preserve on-field performance.

#10 How does the modern football goalkeeper train? - An exploration of expert goalkeeper coaches' skill training approaches
Reference: J Sports Sci. 2019 Jul 16:1-9. doi: 10.1080/02640414.2019.1643202. [Epub ahead of print]
Authors: Otte FW, Millar SK, Hüttermann S
Summary: The football goalkeeper position arguably represents a unique role within the team sport. Despite its highly complex skill demands, research on football goalkeeping has only sporadically examined the position within isolated and limited parameters. In particular, there is limited literature on "modern" skill acquisition training methods and approaches within the field of goalkeeper training. In a cross-cultural study with fifteen expert goalkeeper coaches, researchers here examined the overarching research question of "how does the modern football goalkeeper train?". Semi-structured interviews explored expert coaches' views on critical skills for performance in goalkeeping and the training approaches used to develop these critical skills. Results indicate that four skill sets are considered essential by goalkeeper coaches, these are: decision-making skills, athleticism, mentality, and technical skills. In terms of developing these skills in goalkeeper-specific training, the majority of expert coaches apply a similar microstructure to training sessions. This structure involves a steady progression from simple to complex training tasks, where for large parts, isolated technical training appears to be prioritised over a holistic training approach that integrates technical skills and perceptual-cognitive components (e.g., decision making). Scientific and practical recommendations for researchers and practitioners in the field of football goalkeeper coaching are provided.

#11 A Decision-Analytic Approach to Addressing the Evidence About Football and Chronic Traumatic Encephalopathy
Reference: Semin Neurol. 2019 Jul 16. doi: 10.1055/s-0039-1688484. [Epub ahead of print]
Authors: Brand KP, Finkel AM
Summary: Doubts can be raised about almost any assertion that a particular exposure can lead to an increase in a given adverse health effect. Even some of the most well-accepted causal associations in public health, such as that linking cigarette smoking to increased lung cancer risk, have intriguing research questions remaining to be answered. The inquiry whether an exposure causes a disease is never wholly a yes/no question but ought to follow from an appraisal of the weight of evidence supporting the positive conclusion in light of any coherent theories casting doubt on this evidence and the data supporting these. More importantly, such an appraisal cannot be made sensibly without considering the relative consequences to public health and economic welfare of specific actions based on unwarranted credulity (false positives) versus unwarranted skepticism (false negatives). Here we appraise the weight of evidence for the premise that repeated head impacts (RHIs) in professional football can increase the incidence of chronic traumatic encephalopathy (CTE) and, in turn, cause a variety of cognitive and behavioral symptoms. We first dismiss four logical fallacies that should not affect the appraisal of the weight of evidence. We then examine four alternative hypotheses in which RHI is not associated with CTE or symptoms (or both), and we conclude that the chances are small that the RHI→ CTE→ symptoms link is coincidental or artifactual. In particular, we observe that there are many specific interventions for which, even under a skeptical appraisal of the weight of evidence, the costs of a false positive are smaller than the false negative costs of refusing to intervene.





Latest research in football - week 27 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:


#1 The complex and bidirectional interaction between sex hormones and exercise performance in team sports with emphasis on soccer
Reference: Hormones (Athens). 2019 Jun 29. doi: 10.1007/s42000-019-00115-7. [Epub ahead of print]
Authors: Koundourakis NE, Margioris AN
Summary: A constant topic reported in the lay press is the effect of sex hormones on athletic performance and their abuse by athletes in their effort to enhance their performance or to either boost or sidestep their hard, protracted, and demanding training regimens. However, an issue that it is almost never mentioned is that the athletic training itself affects the endogenous production of androgens and estrogens, while also being affected by them. Among sports, soccer is a particularly demanding activity, soccer players needing to possess high levels of endurance, strength, and both aerobic and anaerobic capacity, with the very great physiological, metabolic, physical, and psychological exertion required of the players being both influenced by sex steroids and, reciprocally, affecting sex steroid levels. This review focuses on the currently available knowledge regarding the complex relationship between athletic training and competition and sex steroid hormone adaptation to the demands of the exercise effort. In the first part of the review, we will examine the effects of endogenous testosterone, estrogen, and adrenal androgens on athletic performance both during training and in competition. In the second part, we will explore the reciprocal effects of exercise on the endogenous sex hormones while briefly discussing the recent data on anabolic androgenic steroid abuse

#2 Isokinetic strength differences between elite senior and youth female soccer players identifies training requirements
Reference: Phys Ther Sport. 2019 Jun 21;39:45-51. doi: 10.1016/j.ptsp.2019.06.008. [Epub ahead of print]
Authors: Eustace SJ, Page RM, Greig M
Summary: The aim was to compare traditional and angle-specific isokinetic strength of eccentric knee flexors and concentric knee extensors in female senior professional and youth soccer players. A total of 34 players (17 seniors [age 25.31 ± 4.51 years; height 167.89 ± 7.04 cm; mass 63.12 ± 7.79 kg] and 17 youths [16.91 ± 1.16 years; height 165.92 ± 4.42 cm; mass 60.07 ± 4.48 kg]) from the Women's Super League 1 completed strength assessments at 180, 270 and 60°∙s-1 participated in this study.  Peak torque (PT), dynamic control ratio (DCR), angle of peak torque (APT), functional range (FR), angle-specific torque (AST) and angle-specific DCR (DCRAST) were compared between age groups. The PT (P = 0.016) AST (P = 0.041) were significantly higher in seniors compared to youths; however APT (P = 0.141), DCR (P = 0.524) FR (P = 0.821) and DCRAST (P = 0.053) were not significant between playing age. The use of absolute and angle-specific strength measures were able to distinguish between female playing ages, whereas DCR and DCRAST was unable to identify differences. The PT and AST metrics may be the most useful metrics to help identify and inform training needs, particularly in youths.

#3 Offensive Transitions in High-Performance Football: Differences Between UEFA Euro 2008 and UEFA Euro 2016
Reference: Front Psychol. 2019 Jun 18;10:1230. doi: 10.3389/fpsyg.2019.01230. eCollection 2019.
Authors: Maneiro R, Casal CA, Álvarez I, Moral JE, López S, Ardá A, Losada JL
Summary: Coaches, footballers and researchers agree that offensive transitions are one of the most important moments in football today. In a sport where defense over attack dominates, with low scores on the scoreboard, the importance of these actions from the offensive point of view becomes very important. Despite this, scientific literature is still very limited on this topic. Therefore, the objectives set out in the present investigation have been two: first, by means of a proportion analysis and the application of a chi-square test, it was intended to describe the possible differences between the offensive transitions made in the UEFA Euro 2008 and UEFA Euro 2016; then, through different multivariate analyzes based on logistic regression models, it was intended to know the possible differences among the proposed models. Using observational methodology as a methodological filter, 1,533 offensive transitions corresponding to the observation of the quarter final, semifinal, and final quarter of UEFA Euro 2008 and UEFA Euro 2016 have been analyzed. The results obtained have shown that offensive transitions between both championships have changed throughout both UEFA Euro, as well as some of the variables or behaviors associated with them (p < 0.05). The predictive models considered, although they have been developed from the same predictor variables, have also yielded different results for both championships, evidencing predictive differences among themselves. These results allow to corroborate that the offensive phase in high level football, specifically in what refers to moments of transition defense-attack, have evolved over these 8 years. At the applied level, the results of this research allow coaches to have current and contemporary information on these actions, potentially allowing them to improve their offensive performance during competition.

#4 Association Between Match Activity, Endurance Levels and Maturity in Youth Football Players
Reference: Int J Sports Med. 2019 Jul 4. doi: 10.1055/a-0938-5431. [Epub ahead of print]
Authors: Francini L, Rampinini E, Bosio A, Connolly D, Carlomagno D, Castagna C
Summary: The aim of the study was to examine the associations between maximal and submaximal field tests with match physical activity and biological maturation in youth football players. Sixty-eight youth football players (U14, U15, U16, U17) performed maximal and submaximal field endurance tests. Biological maturity was estimated calculating the distance from peak height velocity (Y-PHV). Physical match activities were tracked using GPS units and players' post-match rate of perceived exertion (RPE) was recorded. Mainly moderate associations were found between field tests and match activities. Large correlations were found between Yo-Yo Intermittent Recovery test level 1, distance covered at high and very high-speed running, the quantity of very high and maximal metabolic power running. Small to moderate associations between match activities and Y-PHV were observed. The magnitude of correlation between match activities and field tests increased from moderate to large when matches with an RPE>5 were considered. The results provide further evidence of the association between young football players' aerobic performance and match work rate. Submaximal field tests demonstrate ecological validity and may constitute a practical alternative to performing maximal tests. Maturation was found to have a moderate effect on youth players' match work rate.

#5 Postprandial lipaemia 10 and 34 hours after playing football: Does playing frequency affect the response?
Reference: PLoS One. 2019 Jul 2;14(7):e0218043. doi: 10.1371/journal.pone.0218043. eCollection 2019.
Authors: Paul DJ, Nassis GP, Kerouani AC, Bangsbo J
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Summary: Elevated postprandial triglyceride (TG) is associated with increased risk of cardiovascular disease. The time window for the last bout beneficial effect on postprandial lipaemia after football play is unknown. The aim of the present study was to examine whether playing affects postprandial TG during 1.5 day of reduced activity. Eighteen males were randomly allocated to perform either 1 (1FOOT; n = 9; age = 33.0 ± 5.0 yrs; body mass index = 24.2 ± 3.6 kg/m2) or 3 (3FOOT) consecutive days of 60-min 5 vs 5 football (n = 9; age = 32.8 ± 5.2 yrs; body mass index = 26.2 ± 4.1 kg/m2) matches across a 5-day study period. They arrived to the laboratory 10 hrs and 34 hrs after the final football session and blood samples were collected at fasted (0 min) and 45, 90, 240 and 360 min post a high fat load meal. There were non significant increase for postprandial TG AUC (9.1%; p = 0.17; 95%CI = -0.43 to 2.0; ES = -0.23) and iAUC (14.2%; p = 0.43; 95%CI = -0.92 to 1.9; ES = -0.24) between 10 and 34 hrs after the 1FOOT. For the 3FOOT, there was a non significant decrease in postprandial TG AUC (-2.7%; p = 0.73; 95%CI = -2.0 to 1.5; ES = 0.05) and iAUC (-17.5%; p = 0.41; 95%ci = -2.5 to 1.1; ES = 0.31) from 10 to 34 hrs, respectively. Performing three consecutive days of football exercise may offer no greater protective effect for postprandial TG before a period of reduced activity, compared to a single session.

#6 The role of a trauma-sensitive football group in the recovery of survivors of torture
Reference: Torture. 2019;29(1):97-109. doi: 10.7146/torture.v29i1.106613.
Authors: Horn R, Ewart-Biggs R, Hudson F, Berilgen S, Ironside J, Prodromou A
Summary: Whilst there is some preliminary evidence for the benefits of sports-related interventions for survivors of torture, how sport and exercise can contribute to the rehabilitation of torture survivors needs to be better understood. Specifically, this paper aims to: 1) explore the ways in which a football group contributed to the wellbeing of participants and; 2) suggest characteristics of the football group which could potentially contribute to its effectiveness. An exploratory mixed methods study was undertaken with participants and trainers of a joint programme delivered by Arsenal Football Club and Freedom from Torture in London. Individual discussions, group discussions and participatory ranking activities were used which led to the development of an initial programme model. This model was, subsequently, further developed through a variety of data collection methods. Six potential outcomes of involvement in the football group were identified: relationships, a sense of belonging, hope for the future, emotion management, enjoyment, and improved physical health. In addition, the process highlighted factors contributing to the effectiveness of the football group: a sense of safety, therapeutic aims, similar participants, a partnership approach, staff characteristics, other opportunities, and consistency in terms of approach, session content and staff. This exploratory study outlines the potential benefits of the football programme that would require further validation through a case-control study and participant follow-up. A model is put forward as well as a number of recommendations that serve as a starting point for similar programmes and guides academic research in the area.

#7 On-field Rehabilitation Part 2: A 5-Stage Program for the Soccer Player Focused on Linear Movements, Multidirectional Movements, Soccer-Specific Skills, Soccer-Specific Movements, and Modified Practice
Reference: J Orthop Sports Phys Ther. 2019 Jul 10:1-6. doi: 10.2519/jospt.2019.8952. [Epub ahead of print]
Authors: Buckthorpe M, Della Villa F, Della Villa S, Roi GS
Summary: This paper is part 2 of a 2-part series aimed at discussing the key elements of on-field rehabilitation training. In part 1, we described 4 pillars underpinning high-quality on-field rehabilitation: (1) restoring movement quality, (2) physical conditioning, (3) restoring sport-specific skills, and (4) progressively developing chronic training load. In part 2, we describe how the pillars contribute to a 5-stage on-field rehabilitation program to help injured players transition to team practice and match play. We use the example of a soccer player with ambitions to return to sport after anterior cruciate ligament reconstruction. The program moves through 5 field-based training stages: (1) linear movement, (2) multidirectional movement, (3) soccer-specific technical skills, (4) soccer-specific movement, and (5) practice simulation. The staged program is research based and facilitates communication, planning, control, and safety in return to sport following long-term injury.

#8 Anthropometric Profile of Soccer Players as a Determinant of Position Specificity and Methodological Issues of Body Composition Estimation
Reference: Int J Environ Res Public Health. 2019 Jul 5;16(13). pii: E2386. doi: 10.3390/ijerph16132386.
Authors: Leão C, Camões M, Clemente FM, Nikolaidis PT, Lima R, Bezerra P, Rosemann T, Knechtle B
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Summary: The aim of the present study was (a) to describe the anthropometric profile of a large group of soccer players based on different age groups and their playing positions on the field, and (b) to examine the variations of body composition among adult soccer players using diverse equations based on skinfold thickness. A total of 618 Greek soccer players who were grouped by age (i.e., 12-14, 14-16, 16-18, and 18-37 years) and playing position (i.e., goalkeeper, defender, midfielder, and forward) were evaluated for weight, height, and skinfolds. The Pařízková formula was used to estimate the percentage of body fat. Furthermore, for players who were 18 years or older the Reilly and Evans formulas was used to estimate the percentage of body fat. Independent of the age, in this large sample, goalkeepers presented higher values for weight, height and the percentage of body fat estimation as compared with other field positions. An anthropometric pattern was observed in each tactical position, namely, across a specific age of increasing maturation process (14-16 years). With the Pařízková formula, we found a mean (SD) range of variation in the percentage of body fat estimation between 4.87 ± 1.46 and 5.51 ± 1.46 as compared with the Evans formula. The same pattern of differences was found when the Reilly equation was considered. In conclusion, we observed a position specificity of anthropometric characteristics across different age categories. Additionally, the same data supported different validated equations which resulted in large differences in the final outcome estimations.

#9 Effect of a mindfulness programme training to prevent the sport injury and improve the performance of semi-professional soccer players
Reference: Australas Psychiatry. 2019 Jul 8:1039856219859288. doi: 10.1177/1039856219859288. [Epub ahead of print]
Authors: Zadeh MM, Ajilchi B, Salman Z, Kisely S
Summary: Mindfulness improves psychological outcomes. We examined whether greater mindfulness scores were associated with reduced injury rates in soccer players, as well as improved performance at both the individual and team level. This was a parallel-group, pre- and post-test, randomised controlled pilot trial. Forty-five male amateur soccer players from Tehran, Iran, were randomly assigned into experimental (n=23) and control groups (n=22). Outcomes were scores on the mindfulness sport inventory, as well as injury rates and recovery as assessed by a physiotherapist using standardised criteria. Expert observers assessed the effect on individual and team performance. Data were analysed using mixed analysis of variance and, where indicated, its non-parametric alternative, the Friedman test. Significantly greater mindfulness scores in the intervention group were associated with both reduced injury and improved performance. Mindfulness training shows promise in preventing injury and improving performance. The intervention could be applied to other sports and be helpful in clinical settings given the importance of exercise in promoting psychological well-being.

#10 Accuracy of the 2017 international recommendations for clinicians who interpret adolescent athletes' ECGs: a cohort study of 11 168 British white and black soccer players
Reference: Br J Sports Med. 2019 Jul 5. pii: bjsports-2017-098528. doi: 10.1136/bjsports-2017-098528. [Epub ahead of print]
Authors: Malhotra A, Dhutia H, Yeo TJ, Finocchiaro G, Gati S, Bulleros P, Fanton Z, Papatheodorou E, Miles C, Keteepe-Arachi T, Basu J, Parry-Williams G, Prakash K, Gray B, D'Silva A, Ensam B, Behr E, Tome M, Papadakis M, Sharma S.
Summary: The aim was to investigate the accuracy of the recently published international recommendations for ECG interpretation in young athletes in a large cohort of white and black adolescent soccer players. 11 168 soccer players (mean age 16.4±1.2 years) were evaluated with a health questionnaire, ECG and echocardiogram; 10 581 (95%) of the players were male and 10 163 (91%) were white. ECGs were retrospectively analysed according to (1) the 2010 European Society of Cardiology (ESC) recommendations, (2) Seattle criteria, (3) refined criteria and (4) the international recommendations for ECG interpretation in young athletes. The ESC recommendations resulted in a higher number of abnormal ECGs compared with the Seattle, refined and international criteria (13.2%, 4.3%, 2.9% and 1.8%, respectively). All four criteria were associated with a higher prevalence of abnormal ECGs in black athletes compared with white athletes (ESC: 16.2% vs 12.9%; Seattle: 5.9% vs 4.2%; refined: 3.8% vs 2.8%; international 3.6% vs 1.6%; p<0.001 each). Compared with ESC recommendations, the Seattle, refined and international criteria identified a lower number of abnormal ECGs-by 67%, 78% and 86%, respectively. All four criteria identified 36 (86%) of 42 athletes with serious cardiac pathology. Compared with ESC recommendations, the Seattle criteria improved specificity from 87% to 96% in white athletes and 84% to 94% in black athletes. The international recommendations demonstrated the highest specificity for white (99%) and black (97%) athletes and a sensitivity of 86%. The 2017 international recommendations for ECG interpretation in young athletes can be applied to adolescent athletes to detect serious cardiac disease. These recommendations perform more effectively than previous ECG criteria in both white and black adolescent soccer players.

#11 Classification of Soccer and Basketball Players' Jumping Performance Characteristics: A Logistic Regression Approach
Reference: Sports (Basel). 2019 Jul 4;7(7). pii: E163. doi: 10.3390/sports7070163.
Authors: Chalitsios C, Nikodelis T, Panoutsakopoulos V, Chassanidis C, Kollias I
Summary: This study aimed to examine countermovement jump (CMJ) kinetic data using logistic regression, in order to distinguish sports-related mechanical profiles. Eighty-one professional basketball and soccer athletes participated, each performing three CMJs on a force platform. Inferential parametric and nonparametric statistics were performed to explore group differences. Binary logistic regression was used to model the response variable (soccer or not soccer). Statistical significance (p < 0.05) was reached for differences between groups in maximum braking rate of force development (RFDDmax, U79 = 1035), mean braking rate of force development (RFDDavg, U79 = 1038), propulsive impulse (IMPU, t79 = 2.375), minimum value of vertical displacement for center of mass (SBCMmin, t79 = 3.135), and time difference (% of impulse time; ΔΤ) between the peak value of maximum force value (FUmax) and SBCMmin (U79 = 1188). Logistic regression showed that RFDDavg, impulse during the downward phase (IMPD), IMPU, and ΔΤ were all significant predictors. The model showed that soccer group membership could be strongly related to IMPU, with the odds ratio being 6.48 times higher from the basketball group, whereas RFDDavg, IMPD, and ΔΤ were related to basketball group. The results imply that soccer players execute CMJ differently compared to basketball players, exhibiting increased countermovement depth and impulse generation during the propulsive phase.

#12 Bio-banding in Academy Football: Player's Perceptions of a Maturity Matched Tournament
Reference: Ann Hum Biol. 2019 Jul 10:1-28. doi: 10.1080/03014460.2019.1640284. [Epub ahead of print]
Authors: Bradley B, Johnson D, Hill M, McGee D, Kana-Ah A, Sharpin C, Sharp P, Kelly A, Cumming SP, Malina RM
Summary: Individual differences in biological maturation impact player selection and development in youth football. The aim was to evaluate players perceptions of competing in a football tournament where they were matched by maturity rather than chronological age. Participants included male junior footballers from three professional academies (N = 115). The study employed multiple methods of analysis, including one sample means t-tests, equivalence tests, ANOVAs, and thematic analysis of qualitative data derived from open-ended questions. Player's perceived the bio-banding format as providing two main benefits. Early maturing players perceived greater physical and technical challenge, and in turn new opportunities and challenges. Late maturing players perceived less physical and technical challenge, yet greater opportunity to demonstrate technical and tactical abilities. The players reported that they enjoyed and understood the purpose of the bio-banded format, and perceived less risk for injury. Players in all three maturity groups reported more opportunity to engage in leadership behaviours, influence game-play, and express themselves on the ball in the bio-banded format. Bio-banding may facilitate development for both early and late maturing academy players by presenting new learning environments and challenges.

#13 The association between the isokinetic muscle strength and lower extremity injuries in young male football players
Reference: Phys Ther Sport. 2019 Jun 29;39:76-81. doi: 10.1016/j.ptsp.2019.06.013. [Epub ahead of print]
Authors: Namazi P, Zarei M, Hovanloo F, Abbasi H
Summary: Validating any screening test to predict and prevent football injuries is in need of identifying related risk factors through prospective designs. In spite of the extensive use of strength testing in football players, there are limited studies investigating the relationship between isokinetic muscle strength and injury risk in young football players. The present study aimed to evaluate the relationship between isokinetic strength and the risk of lower extremity injury among Iranian young football players. Seventy three U-21 football players participated in this study. Isokinetic strength of hip, knee and ankle muscles were measured using the Isokinetic system pro 4. Injuries and exposure in training and matches were registered prospectively by club medical staff for one season. Significant relationships were revealed between the isokinetic strength of hip abductor and adductor muscles, and isokinetic strength ratio of hip abductor/adductor muscles at an angular speed of 30°/sec, the isokinetic strength of hip abductor muscles at 90°/sec, and isokinetic strength of knee flexor and extensor muscles at 60°/sec and knee flexor/extensor strength ratio at angular velocities of 60°/sec with the injury occurrence among football players. Lower extremity isokinetic strength indices are associated with injuries in young male football players.

#14 A Lethal Blow to the Chest as an Underdiagnosed Cause of Sudden Death in United Kingdom Sports (Football, Cricket, Rugby)
Reference: Am J Cardiol. 2019 Jun 7. pii: S0002-9149(19)30629-0. doi: 10.1016/j.amjcard.2019.05.050. [Epub ahead of print]
Authors: Cooper S, Woodford NW, Maron BJ, Harris KM, Sheppard MN
Summary: Nonpenetrating blunt force trauma to the front of the chest can lead to commotio cordis, a cardiac rhythm disturbance, which can result in cardiac arrest and death. The condition is particularly noted during sport. No series of such cases has been published in the UK. This study is a retrospective analysis of a database of 6000 cases of sudden cardiac death examining commotio cordis in the setting of collapse and death shortly following a blow to the precordium where no structural heart disease was identified at autopsy. Of the 17 cases, 16 were male, and 11 were 18 years old or younger. Eleven occurred whilst playing sport while 6 involved physical interaction including assault. The most common circumstance of death involved a youth being struck in the chest by a ball during sporting activity. In conclusion, this study demonstrates that cases of commotio cordis in the UK follow a similar circumstantial and age profile to those reported in the United States, and indicates that ball sports such as football, cricket, and rugby expose young participants to a similar risk. There is currently no nation-wide registry of deaths occurring during sporting activity in the UK, and although the true incidence of this condition is not currently known, it is most probably under-recognised and underdiagnosed.





Latest research in football - week 26 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:


#1 Changes in Lactate Kinetics Underpin Soccer Performance Adaptations to Cycling-Based Sprint Interval Training
Reference: Eur J Sport Sci. 2019 Jun 24:1-24. doi: 10.1080/17461391.2019.1635650. [Epub ahead of print]
Authors: Thom G, Kavaliauskas M, Babraj J
Summary: In adolescent soccer, 23% of the distance covers happens at speeds above onset of blood lactate accumulation which suggests that lactate kinetics may be important for soccer performance. We sought to determine the effectiveness of sprint interval training (SIT) on changing performance and lactate kinetics in adolescent soccer players. Thirteen elite soccer academy players (age 15 ± 0.5y) underwent baseline testing (0-10m and 10-20m sprint performance, Wingate anaerobic Test (WaNT) with blood lactate measurements and incremental VO2 peak test) before being allocated to control or SIT group. The control group maintained training whilst the HIT group carried out twice-weekly all-out effort cycle sprints consisting of 6 x 10sec sprint with 80sec recovery. There were significant time x group interactions for 10- 20m sprint time (Control pre: 1.32 ± 0.07s post: 1.35 ± 0.08s; SIT pre: 1.29 ± 0.04s post: 1.25 ± 0.04s; p=0.01), Peak Power (Control pre: 13.1 ± post: 13.2 ± 1.47; SIT pre: 12.4 ± 1.3 post: 15.3 ±; p=0.01) and time to exhaustion (Control pre: 596 ± 62s post: 562 ± 85s; SIT pre: 655 ± 54s post: 688 ± 55s; p=0.001). The changes in performance were significantly correlated to changes in lactate kinetics (power: r=0.55; 10-20m speed: r=-0.54; time to exhaustion: r=0.55). Therefore, cycle based SIT is an effective training paradigm for elite adolescent soccer players and the improvements in performance are associated with changes in lactate kinetics.

#2 The Validity and Reliability of Live Football Match Statistics From Champdas Master Match Analysis System
Reference: Front Psychol. 2019 Jun 11;10:1339. doi: 10.3389/fpsyg.2019.01339. eCollection 2019.
Authors: Gong B, Cui Y, Gai Y, Yi Q, Gómez MÁ
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Summary: The aim of the present study was to investigate the validity of match variables and the reliability of Champdas Master System used by trained operators in live association football match. Twenty professional football coaches voluntarily participated in the validation of match variables used in the System. Four well-trained operators divided into two groups that independently analyzed a match of Spanish La Liga. The Aiken's V averaged at 0.84 ± 0.03 and 0.85 ± 0.03 for the validation of indicators. The high Kappa values (Operator 1: 0.92, 0.90; Operator 2: 0.91, 0.88), high intra-class correlation coefficients (varied from 0.93 to 1.00), and low typical errors (varied from 0.01 to 0.34) between the first and second data collection represented a high level of intra-operator reliability. The Kappa values for the inter-operator reliability of were 0.97 and 0.89. The intra-class correlation coefficients and typical errors ranged from 0.90 to 1.00 and ranged from 0.01 to 0.24 for two independent operators within two data collections. The results suggest that the Champdas Master system can be used validly and reliably to gather live football match statistics by well-trained operators. Therefore, the data obtained by the company can be used by coaches, managers, researchers and performance analysts as valid match statistics from players and teams during their professional tasks and investigations.

#3 Coach Turnover in Top Professional Brazilian Football Championship: A Multilevel Survival Analysis
Reference: Front Psychol. 2019 Jun 6;10:1246. doi: 10.3389/fpsyg.2019.01246. eCollection 2019.
Authors: Tozetto AB, Carvalho HM, Rosa RS, Mendes FG, Silva WR, Nascimento JV, Milistetd M
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Summary: In this study, we examined the probability of coaches' survival in the top Brazilian professional football championship considering variation across the competitive seasons between 2012 and 2017, considering a multilevel framework. We also considered whether previous coaching experience in the top Brazilian professional football championship would change the probability of coaches' survival across the season. The data considered 4,560 games from the top professional Brazilian football league (Campeonato Brasileiro Série A) between the 2012 and 2017 seasons. At the start of each season, the coach from each team was followed, being recorded at the time the event occurred, i.e., the coach being sacked. A total survival of 120 coaches was considered between the seasons of 2012 and 2017, i.e., 20 coaches at the beginning of each season. Coaches were assigned as novice (no previous experience as head coach in the top Brazilian championship) or experienced (with at least some previous experience as head coach in the top Brazilian championship). Data were available and extracted from the official website of the Brazilian Football Confederation. On average and considering un-pooled observations, the median life of a coach was about 16.5 rounds. Considering variation between 2012 and 2017 seasons, only about 26.3% (95% CI: 18.2-36.1) of the coaches ended a season without being sacked. By mid-season, at round 19, the probability of coaches' survival was 0.42 (95% CI: 0.32-0.53). Variation between season on survival estimates per round was substantial (between-season standard deviation = 0.48, 95% credible intervals: 0.25-0.95; corresponding to an inverse logit = 0.62, 95% CI: 0.56-0.72). There was no substantial variation between novice and experienced coaches' survival probability. The present results expose the vulnerability of the coaching context in Brazilian football, potentially highlighting an excessive emphasis on short-term results to mediate club management decisions.

#4 Incidence and Prevalence of Borrelia burgdorferi Antibodies in Male Professional Football Players
Reference: Clin J Sport Med. 2019 May 30. doi: 10.1097/JSM.0000000000000758. [Epub ahead of print]
Authors: Breitbart P, Meister S, Meyer T, Gärtner BC
Summary: Infections with Borrelia burgdorferi can cause Lyme disease with multiorganic involvement such as (myo)carditis or joint manifestations. Musculoskeletal complaints possibly mimicking some of these symptoms are common among elite athletes. This study aimed to determine seroprevalence and incidence of B. burgdorferi antibodies in professional football players. Five hundred thirty-five men in the first and second German league participated in this study. Two screening assays were used to examine immunoglobulin M (IgM) and immunoglobulin G (IgG) against B. burgdorferi: an enzyme immunoassay (EIA) and a chemiluminescence assay (CLIA). In case of a positive or equivocal result, an immunoblot including in vivo antigens was performed. Course of IgM and IgG against B. burgdorferi in overall 1529 blood samples were used as outcome measures.  A total of 96.4% of all results were concordant between EIA and CLIA. Considering only samples with identical results in both assays, prevalence was 1.6%. A positive IgM was detected in 2.3%. No player showed any symptoms of Lyme disease. A seroconversion to IgG was not found. Three players developed a positive IgM corresponding to an incidence of 1032/100 000 person-years. Depending on the assay, 49% to 75% of positive or equivocal screening results could not be confirmed by immunoblot. Seroprevalence and incidence of B. burgdorferi among healthy male professional football players are low. Therefore, infections with B. burgdorferi have to be regarded a rare differential diagnosis in professional football in Central Europe. The low confirmation rate of positive screening assays points to an unspecific immune activation.

#5 Use of viscosupplementation for the recovery of active football players complaining of knee pain
Reference: Open Access J Sports Med. 2019 Jun 6;10:87. doi: 10.2147/OAJSM.S212442. eCollection 2019.
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#6 External Load Variables Affect Recovery Markers up to 72 h After Semiprofessional Football Matches
Reference: Front Physiol. 2019 Jun 4;10:689. doi: 10.3389/fphys.2019.00689. eCollection 2019.
Authors: Wiig H, Raastad T, Luteberget LS, Ims I, Spencer M
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Summary: Player tracking devices are commonly used to monitor external load from training and matches in team sports. Yet, how the derived external load variables relate to fatigue and recovery post-training or post-match is scarcely researched. The objective was, therefore, to investigate how external load variables affect recovery markers up to 72 h post-match. Semiprofessional players from six teams wore tracking devices during three experimental football matches. External load variables including individual playing duration, total distance, PlayerLoad™, high-intensity running, and high-intensity events were derived from the tracking devices, and blood samples and performance tests from 24-59 players were undertaken post-match. The effect of the external load variables on creatine kinase, myoglobin, and countermovement jump at 1, 24, 48, and 72 h, and 30-m sprint and Yo-Yo intermittent recovery tests level 1 at 72 h post-match, were modeled. Effects were gauged as two standard deviations of the external load and interpreted as the difference between a typical high-load and a typical low-load match. The effects were evaluated with 90% confidence intervals and magnitude-based inferences. High-intensity running had very likely substantial effects on creatine kinase and myoglobin (moderate factor increases of 1.5-2.0 and 1.3-1.6 respectively), while duration, total distance, and HIE showed small, likely substantial effects. PlayerLoad™ and total distance had likely substantial effects on 30-m sprint time (small increases of 2.1-2.6%). Effects on countermovement jump performance were generally non-substantial. Despite these relationships, the uncertainty was too large to predict the recovery of individual players from the external load variables. This study provides evidence that external load variables have an effect on recovery markers up to 72 h post-match. Hence, tracking external load in matches may be helpful for practitioners when managing training load and recovery strategies post-match. However, it is recommended that several different external load variables are monitored. Future research should continue to address the problem of predicting recovery from external load variables.

#7 Effect of biological maturation on strength-related adaptations in young soccer players
Reference: PLoS One. 2019 Jul 5;14(7):e0219355. doi: 10.1371/journal.pone.0219355. eCollection 2019.
Authors: Peña-González I, Fernández-Fernández J, Cervelló E, Moya-Ramón M
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Summary: Strength training is crucial for soccer players' long-term development at early ages and the biological maturation may influence specific strength-training adaptations. The aim of this study was to propose a strength-training programme for the strength development of pre-pubertal players and to analyse the adaptations to this training programme in players with different maturity status. One hundred and thirty young male soccer players participated in an 8-week strength-training programme consisting of two sessions per week (20-minutes of a combination of plyometric and resistance exercises) which was conducted prior to their normal soccer training. Three maturity groups were defined according to the years from/to their peak height velocity (PHV) as Pre-, Mid- and Post-PHV. Initial differences between the maturity groups were found in anthropometrical (weight and height) and physical performance variables (One Repetition Maximum (RM), Peak Power output (PP), 30-m sprint and T-test). The strength-training programme was beneficial for the three maturity groups (p< 0.05) with general greater improvements for the Pre- and Mid-PHV groups, with large effects in RM, PP and T-test, than for the Post-PHV group (moderate effects). The strength-training programme proposed in the present study seems to be positive for the strength-related development in young soccer players especially for Pre- and Mid-PHV players. The differences in the training adaptations for players with different maturity status suggest the individualization of the training stimulus for the correct long-term development of the players.

#8 Gender but not diabetes, hypertension or smoking affects infarct evolution in ST-elevation myocardial infarction patients - data from the CHILL-MI, MITOCARE

Reference: BMC Cardiovasc Disord. 2019 Jul 3;19(1):161. doi: 10.1186/s12872-019-1139-7.
and SOCCER trials.
Authors: Nordlund D, Engblom H, Bonnet JL, Hansen HS, Atar D, Erlinge D, Ekelund U, Heiberg E, Carlsson M, Arheden H
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Summary: Infarct evolution rate and response to acute reperfusion therapy may differ between patients, which is important to consider for accurate management and treatment of patients with ST-elevation myocardial infarction (STEMI). The aim of this study was therefore to investigate the association of infarct size and myocardial salvage with gender, smoking status, presence of diabetes or history of hypertension in a cohort of STEMI-patients. Patients (n = 301) with first-time STEMI from the three recent multi-center trials (CHILL-MI, MITOCARE and SOCCER) underwent cardiac magnetic resonance (CMR) imaging to determine myocardium at risk (MaR) and infarct size (IS). Myocardial salvage index (MSI) was calculated as MSI = 1-IS/MaR. Pain to balloon time, culprit vessel, trial treatments, age, TIMI grade flow and collateral flow by Rentrop grading were included as explanatory variables in the statistical model. Women (n = 66) had significantly smaller MaR (mean difference: 5.0 ± 1.5% of left ventricle (LV), p < 0.01), smaller IS (mean difference: 5.1 ± 1.4% of LV, p = 0.03), and larger MSI (mean difference: 9.6 ± 2.8% of LV, p < 0.01) compared to men (n = 238). These differences remained significant when adjusting for other explanatory variables. There were no significant effects on MaR, IS or MSI for diabetes, hypertension or smoking. Female gender is associated with higher myocardial salvage and smaller infarct size suggesting a pathophysiological difference in infarct evolution between men and women.

#9 Effects of Age on Physical Match Performance in Professional Soccer Players
Reference: J Strength Cond Res. 2019 Jul 1. doi: 10.1519/JSC.0000000000003244. [Epub ahead of print]
Authors: Rey E, Costa PB, Corredoira FJ, Sal de Rellán Guerra A
Summary: This study aimed to evaluate the effects of age using a large-scale analysis of match physical performance in professional soccer players. A total of 10,739 individual match observations were undertaken on outfield players competing in the first and second divisions of the Spanish soccer professional leagues during the 2017-2018 season, using a computerized tracking system (TRACAB, Chyronhego, New York, USA). The players were classified into five positions and into 5 age groups (<20 years, 20-24.9 years, 25-29.9 years, 30-34.9 years, and ≥35 years). The results showed that (a) professional soccer players aged ≥30 years exhibit a significant decrease (p < 0.01) in the total distance covered, medium-speed running distance, high-speed running (HSR) distance, very HSR (VHSR) distance, sprint distance, and maximum running speed compared with younger players (<30 years); (b) professional soccer players aged ≥35 years exhibit a significant decrease (p < 0.01) in the number of HSR, number of VHSR, and number of sprints compared with younger players (<35 years); and (c) all playing positions reduced their physical performance; however, external midfielders were less affected by age effects. In conclusion, this study demonstrates players' physical match performance reduces with increasing age. Such findings may help coaches and managers to better understand the effects of age on match-related physical performance and may have the potential to assist in decisions regarding recruitment and player list management within professional soccer clubs.

#10 Biomechanical Associates of Performance and Knee Joint Loads During A 70-90° Cutting Maneuver in Subelite Soccer Players
Reference: J Strength Cond Res. 2019 Jul 1. doi: 10.1519/JSC.0000000000003252. [Epub ahead of print]
Authors: McBurnie AJ, DosʼSantos T, Jones PA
Summary: The aim of this study was to explore the "performance-injury risk" conflict during cutting, by examining whole-body joint kinematics and kinetics that are responsible for faster change-of-direction (COD) performance of a cutting task in soccer players, and to determine whether these factors relate to peak external multiplanar knee moments. 34 male soccer players (age: 20 ± 3.2 years; body mass: 73.5 ± 9.2 kg; height: 1.77 ± 0.06 m) were recruited to investigate the relationships between COD kinetics and kinematics with performance and multiplanar knee joint moments during cutting. Three-dimensional motion data using 10 Qualisys Oqus 7 infrared cameras (240 Hz) and ground reaction force data from 2 AMTI force platforms (1,200 Hz) were collected to analyze the penultimate foot contact and final foot contact (FFC). Pearson's or Spearman's correlations coefficients revealed performance time (PT), peak external knee abduction moment (KAM), and peak external knee rotation moment (KRM) were all significantly related (p < 0.05) to horizontal approach velocity (PT: ρ = -0.579; peak KAM: ρ = 0.414; peak KRM: R = -0.568) and FFC peak hip flexor moment (PT: ρ = 0.418; peak KAM: ρ = -0.624; peak KRM: ρ = 0.517). Performance time was also significantly (p < 0.01) associated with horizontal exit velocity (ρ = -0.451) and, notably, multiplanar knee joint loading (peak KAM: ρ = -0.590; peak KRM: ρ = 0.525; peak KFM: ρ = -0.509). Cohen's d effect sizes (d) revealed that faster performers demonstrated significantly greater (p < 0.05; d = 1.1-1.7) multiplanar knee joint loading, as well as significantly greater (p < 0.05; d = 0.9-1.2) FFC peak hip flexor moments, PFC average horizontal GRFs, and peak knee adduction angles. To conclude, mechanics associated with faster cutting performance seem to be "at odds" with lower multiplanar knee joint loads. This highlights the potential performance-injury conflict present during cutting.

#11 A retrospective study of mechanisms of anterior cruciate ligament injuries in high school basketball, handball, judo, soccer, and volleyball
Reference: Medicine (Baltimore). 2019 Jun;98(26):e16030. doi: 10.1097/MD.0000000000016030.
Authors: Takahashi S, Nagano Y, Ito W, Kido Y, Okuwaki T
Summary: The purpose of this study was to analyze the mechanism of anterior cruciate ligament (ACL) injuries among male and female high school students across several different sports to understand ACL injury trends.A total of 1000 cases involving high school students who suffered ACL injuries during school activities (soccer, basketball, volleyball, handball, and judo) and who received insurance benefits through the Injury and Accident Mutual Aid Benefit System, were included to clarify the various mechanisms of ACL injuries. The mechanism of ACL injury was divided into contact and non-contact injuries. Contact injuries were further divided into direct and indirect contact injuries. Non-contact ACL injuries were also further divided into landing injuries, which involved jump-landing movements, and cutting and stopping injuries, which involved movement with a change of direction and deceleration.Overall, 99.0% of judo ACL injuries were categorized as contact ACL injuries. With regards to ball sports, the number of non-contact ACL injuries among basketball, volleyball, and handball players was significantly higher than the number of contact injuries (67.0%, 86.5%, and 68.5% respectively). With regards to female soccer and basketball players, the number of indirect ACL injuries was higher than direct injuries (72.2% and 76.7%, respectively).Volleyball was associated with a higher rate of non-contact injuries. Soccer, basketball, and handball were associated with more or similar rates of indirect and non-contact injuries than direct injuries. Judo was associated with a higher rate of contact injuries.

#12 Self-reported head injury symptoms exacerbated in those with previous concussions following an acute bout of purposeful soccer heading
Reference: Res Sports Med. 2019 Jun 30:1-14. doi: 10.1080/15438627.2019.1635130. [Epub ahead of print]
Authors: Kaminski TW, Thompson A, Wahlquist VE, Glutting J
Summary: Rates of concussion in soccer are high, especially in female players. The primary aim of this study was to examine differences in self-reported concussion-related symptoms (CRS), balance (BESS), and neurocognitive performance (ImPACT) following an acute bout of soccer heading in a group of female collegiate players with and without a history of concussion. Eighty-seven players with 0 to 3+ previous concussions participated. The measurement variables were assessed before and after heading sessions; including one linear and one rotational bout. Players with concussion histories reported more CRS than their non-concussed teammates both before and after the heading sessions. Balance and neurocognitive scores were generally unaffected. This finding should heighten our awareness to carefully monitor soccer players who have experienced concussions and be aware that they may develop concussion-like symptoms, especially after acute bouts of heading either during practice or in matches. The long-term implications of this finding remain unknown.





Latest research in football - week 25 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Correction: Six different football shoes, one playing surface and the weather; Assessing variation in shoe-surface traction over one season of elite football
Reference: PLoS One. 2019 Jun 19;14(6):e0218865. doi: 10.1371/journal.pone.0218865. eCollection 2019.
Authors: Thomson A, Whiteley R, Wilson M, Bleakley C.
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#2 Growing Pains: Maturity Associated Variation in Injury Risk in Academy Football
Reference: Eur J Sport Sci. 2019 Jun 19:1-21. doi: 10.1080/17461391.2019.1633416. [Epub ahead of print]
Authors: Johnson DM, Williams S, Bradley B, Sayer S, Murray Fisher J, Cumming S
Summary: Reducing injuries to youth players is of primary importance to academies, as injuries can result in a significant loss in both training and match time, as well as negatively affecting player development. In total, 76 talented young football players were analysed over two full competitive seasons. The injury incidence and burden for all non-contact and overuse injuries were recorded. Exposure was calculated as the total number of competitive matches hours played. Somatic maturation was estimated by expressing the current height of each player as a percentage of their predicted adult height (Roche, Tyleshevski, & Rogers, 1983). The period of circa-peak height velocity (PHV) (24.5 injuries per 1000 h) was associated with a significantly higher injury incidence rate and burden compared to pre-PHV (11.5 injuries per 1000 h; RR:2.15, 95%CI:1.37-3.38, P < .001). No significant differences in injury risk between maturity timing groups were observed. The interaction effect between maturity status and maturity timing confirmed there is a risk period circa-PHV, but this was not dependent on maturity timing. The main practical application of this study is that football academies should regularly assess the maturity status of young footballers to identify those players with increased susceptibility to injury. Moreover, academies should individualise training and injury prevention strategies based on maturation.

#3 Epidemiological Study on Professional Football Injuries During the 2011 Copa America, Argentina
Reference: Rev Bras Ortop. 2013 Jun 20;48(2):131-136. doi: 10.1016/j.rboe.2012.09.003. eCollection 2013 Mar-Apr.
Authors: Pedrinelli A, Filho GARDC, Thiele ES, Kullak OP
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Summary: Develop an epidemiological study of injuries occurred among male professional football players during the Copa America 2011, held in Argentina. We conducted a retrospective study of injuries sustained during the 43rd edition of the Copa America football in Argentina, in 2011. The lesions were evaluated by the medical department of the selections and reported to the CONMEBOL. The data were compiled and reported in accordance with rules established by the FIFA Medical Assessment and Research Centre (F-MARC) in 2005. There was a higher prevalence of lesions in the lower limbs. Thighs and knees were the most affected segments. The most frequent diagnoses were muscle injuries. The injuries were mostly minor degrees of severity and there was little difference in the prevalence of lesions according to the stages of the match, with slight predominance in the final 15 minutes. The incidence of lesions per 1,000 game hours was similar to the average found in the literature. The results obtained allowed us to outline a profile of the prevalence, distribution per body segment, minute in which occurred and severity of injuries in professional football players of participating teams in the Copa America 2011 in Argentina. The extreme rigor of referees may be partly attributed to the highly competitive nature of international tournaments. However, this results cannot be considered definitive because of the need to be compared to other epidemiological studies with same design using similar concepts and criteria.

#4 Every second retired elite female football player has MRI evidence of knee osteoarthritis before age 50 years: a cross-sectional study of clinical and MRI outcomes
Reference: Knee Surg Sports Traumatol Arthrosc. 2019 Jun 17. doi: 10.1007/s00167-019-05560-w. [Epub ahead of print]
Authors: Prien A, Boudabous S, Junge A, Verhagen E, Delattre BMA, Tscholl PM
Summary: The purpose was to assess knee health in retired female football players, using magnetic resonance imaging (MRI) and self-report. The focus of analysis were degenerative changes of the tibiofemoral joint, and their relationship to osteoarthritis symptoms and previous knee injury. Forty-nine retired elite, female football players (98 knees) aged 37 years on average participated. Tibiofemoral cartilage and meniscus status of both knees were evaluated using MRI and graded according to modified Outerbridge and Stoller classifications, respectively. Symptoms were assessed through a standardised questionnaire (Knee Osteoarthritis Outcome Score: KOOS). Knee injury history was recorded via a semi-structured interview. To investigate how injury variables relate to outcomes, binary logistic regression models were used and reported with odds ratios (OR). Fifty-one per cent of players (n = 25) fulfilled the MRI criterion for knee osteoarthritis, 69.4% (n = 34) had substantial meniscal loss and 59.6% (n = 28) reported substantial clinical symptoms. Chondral- and meniscal loss were associated with significantly lower scores on three of five KOOS subscales (p < .05). Both chondral and meniscal loss were significantly predicted by previous traumatic knee injury (OR = 4.6, OR = 2.6), the injury affecting the non-striking leg (OR = 8.6, OR = 10.6) and type of injury; participants with combined ACL/meniscus injuries had the highest risk for substantial chondral and meniscal loss (OR = 14.8, OR = 9.5). Chondral loss was significantly predicted by isolated meniscus injury treated with partial meniscectomy (OR = 5.4), but not by isolated reconstructed ACL injury. Clinical symptoms were only significantly predicted by previous traumatic knee injury (OR = 5.1). Serious degenerative changes were found in a high number of retired female football players' knees 10 years after their career. Meniscal integrity is key for knee osteoarthritis outcomes in young adults, and thus, its preservation should be a priority.

#5 Quantifying the physical loading of five weeks of pre-season training in professional soccer teams from Dutch and Portuguese leagues
Reference: Physiol Behav. 2019 Jun 24;209:112588. doi: 10.1016/j.physbeh.2019.112588. [Epub ahead of print]
Authors: Clemente FM, Seerden G, van der Linden CMI
Summary: The purpose of this study was to quantify the physical loads of programmed pre-season training in four different professional Dutch and Portuguese soccer teams. Eighty-nine professional players were monitored daily during a five-week period. We monitored the physical loading of training by measuring the external load measures of total distance covered, walking distance, jogging distance, running distance, sprinting distance, high-intensity sprint distance, player's load and number of sprints using a 10 Hz GPS technology. Weekly external load and intra-week external load variations were tested. Repeated measures did not show significant differences between weeks in terms of weekly loads based on total distance and sprinting distance. Significant differences were found between training days considering the duration (p = .011), walking distance (p = .017), running distance (p = .004), player's load (p = .040) and number of sprints (p = .006). Variations between weeks were small, however intra-week variations were observed namely considering the measures associated with great volume and lower intensity.

#6 Technical and tactical performance indicators discriminating winning and losing team in elite Asian beach soccer tournament
Reference: PLoS One. 2019 Jun 27;14(6):e0219138. doi: 10.1371/journal.pone.0219138. eCollection 2019.
Authors: Muazu Musa R, P P Abdul Majeed A, Abdullah MR, Ab Nasir AF, Arif Hassan MH, Mohd Razman MA
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Summary: The present study aims to identify the essential technical and tactical performance indicators that could differentiate winning and losing performance in the Asian elite beach soccer competition. A set of 20 technical and tactical performance indicators namely; shot back-third, shot mid-third, shot front-third, pass back-third, pass mid-third, pass front-third, shot in box, shot outbox, chances created, interception, turnover, goals scored 1st period, goals scored 2nd period, goals scored 3rd period, goals scored extra time, tackling, fouls committed, complete save, incomplete save and passing error were observed during the beach soccer Asian Football Confederation tournament 2017 held in Malaysia. A total of 23 matches from 12 teams were notated using StatWatch application in real-time. Discriminant analysis (DA) of standard, backward as well stepwise modes were used to develop a model for the winning (WT) and losing team (LT) whilst Mann-Whitney U test was utilized to ascertain the differences between the WT and LT with respect to the performance indicators evaluated. The standard backward, forward and stepwise discriminates the WT and the LT with an excellent accuracy of 95.65%, 91.30% and 89.13%, respectively. The standard DA model discriminated the teams from seven performance indicators whilst both the backward and forward stepwise identified two performance indicators. The Mann-Whitney U test analysis indicated that the WT is statistically significant from the LT based on the performance indicators determined from the standard mode model of the DA. It was demonstrated that seven performance indicators namely; shot front-third, pass front-third, chances created, goals scores at the 1st period, goals scored at the 2nd period, goals scored at 3rd period were directly linked to a successful performance whilst the incomplete save by the keeper attribute towards the poor performance of the team. The present finding could serve useful to the coaches as well as performance analysts as a measure of profiling successful performance and enables team improvement with respect to the associated performance indicators.

#7 Post-activation Potentiation: Effects of Different Conditioning Intensities on Measures of Physical Fitness in Male Young Professional Soccer Players
Reference: Front Psychol. 2019 Jun 6;10:1167. doi: 10.3389/fpsyg.2019.01167. eCollection 2019.
Authors: Petisco C, Ramirez-Campillo R, Hernández D, Gonzalo-Skok O, Nakamura FY, Sanchez-Sanchez J
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Summary: The aim of this study was to compare the effects of different warm-up conditioning intensities on the physical fitness (i.e., post-activation potentiation -PAP), of professional male field soccer players. Athletes (n = 10; age: 21.6 ± 3.2 years) completed a control warm-up and warm-ups aimed to induce PAP, in random and counterbalanced order. After control and experimental warm-up sessions participants completed a triple hop test with the dominant (H3Jd) and a non-dominant (H3Jnd) leg, a squat jump (SJ), a countermovement jump (CMJ), a change of direction ability (COD) test, a repeated sprint with a COD (RSCOD) test and a linear 30-m sprint test (S-30). The control warm-up (WU) protocol was designed according to athlete's regular warm-up practice. The experimental warm-ups included the same exercises as the WU, with addition of one set of half-back squats for 10 repetitions at 60%, 5 repetitions at 80%, and 1 repetition at 100% of 1RM (60%-1RM, 80%-1RM and 100%-1RM, respectively.) Threshold values for Cohen's effect sizes (ES) were calculated and used for group's comparison. Likely to most likely improvements were shown in H3Jd (ES = 0.52), H3Jnd (ES = 0.51), COD (ES = 0.38), fasted sprint (RSCODb) (ES = 0.58) and the total time of all sprints (RSCODt) (ES = 0.99) only after the 80%-1RM protocol in comparison to the WU. Conversely, 100%-1RM and 60%-1RM protocols, compared to WU, induced possibly to most likely poorer performance in all jumps, COD and RSCODb (ES = -0.07 to -1.03 and ES = -0.48 to -0.91, respectively). Possibly to most likely improvements were shown in all jumps, COD, RSCODb and RSCODt after the 80%-1RM warm-up protocol in comparison to the 100%-1RM and 60%-1RM warm-up protocols (ES = 0.35 to 2.15 and ES = 0.61 to 1.46, respectively). A moderate warm-up intensity (i.e., 80%-1RM back squat) may induce greater PAP, including improvements in jumping, repeated and non-repeated change of direction speed in male soccer players.

#8 The Effect of Phase Change Material on Recovery of Neuromuscular Function Following Competitive Soccer Match-Play
Reference: Front Physiol. 2019 Jun 6;10:647. doi: 10.3389/fphys.2019.00647. eCollection 2019.
Authors: Brownstein CG, Ansdell P, Škarabot J, McHugh MP, Howatson G, Goodall S, Thomas K
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Summary: Cryotherapy is commonly implemented following soccer match-play in an attempt to accelerate the natural time-course of recovery, but the effect of this intervention on neuromuscular function is unknown. The aim of the present study was to examine the effect of donning lower-body garments fitted with cooled phase change material (PCM) on recovery of neuromuscular function following competitive soccer match-play. Using a randomized, crossover design, 11 male semi-professional soccer players wore PCM cooled to 15°C (PCMcold) or left at ambient temperature (PCMamb; sham control) for 3 h following soccer match-play. Pre-, and 24, 48, and 72 h post-match, participants completed a battery of neuromuscular, physical, and perceptual tests. Maximal voluntary contraction force (MVC) and twitch responses to electrical (femoral nerve) and magnetic (motor cortex) stimulation (TMS) during isometric knee-extension and at rest were measured to assess central nervous system (CNS) (voluntary activation, VA) and muscle contractile (quadriceps potentiated twitch force, Qtw,pot) function. Fatigue and perceptions of muscle soreness were assessed via visual analog scales, and physical function was assessed through measures of jump [countermovement jump (CMJ) height and reactive strength index (RSI)] performance. A belief questionnaire was completed pre- and post-intervention to determine the perceived effectiveness of each garment. Competitive soccer match-play elicited persistent decrements in MVC, VA measured with femoral nerve stimulation, Qtw,pot, as well as reactive strength, fatigue and muscle soreness (P < 0.05). Both MVC and VA were higher at 48 h post-match after wearing PCMcold compared with PCMamb (P < 0.05). However, there was no effect of PCM on the magnitude or time-course of recovery for any other neuromuscular, physical function, or perceptual indices studied (P > 0.05). The belief questionnaire revealed that players perceived that both PCMcold and PCMamb were moderately effective in improving recovery, with no difference between the two interventions (P = 0.56).: Although wearing cooled PCM garments improved MVC and VA 48 h following match-play, the lack of effect on measures of physical function or perceptual responses to match-play suggest that PCM offers a limited benefit to the recovery process. The lack of effect could have been due to the relatively small magnitude of change in most of the outcome measures studied.

#9 What Frequency of Technical Activity Is Needed to Improve Results? New Approach to Analysis of Match Status in Professional Soccer
Reference: Int J Environ Res Public Health. 2019 Jun 25;16(12). pii: E2233. doi: 10.3390/ijerph16122233.
Authors: Konefał M, Chmura P, Rybka K, Chmura J, Huzarski M, Andrzejewski M
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Summary: The aim of the research detailed here has been to assess the frequency with which football players engage in technical activity of various different types, in relation to seven phases of a game associated with changes in match status. To this end, 2016-2017 domestic-season matches in Germany's Bundesliga were analyzed, the relevant data being retrieved using an Opta Sportsdata Company system. Technical activity taken into consideration included shots, passes, ball possession, dribbles, and tackles. It was found that there was a large impact of frequency of shots on target (H = 466.999(6); p = 0.001) in relation to the different match-status phases. Furthermore, moderate effect sizes were then obtained for frequency of shots (H = 187.073(6); p = 0.001), frequency of passes (H = 133.547(6); p = 0.001), and percentage of ball possession (H = 123.401(6); p = 0.001). The implication would be that a team trying to change the match score of a game experienced at a given moment in a more favorable direction will need to raise the frequency and accuracy of passes, the percentage of ball possession, and the percentage of tackles ending in success. The maintenance of a winning match status requires a high frequency of occurrence of shots and shots on target as well as greater frequency and effectiveness of dribbling. The main finding from our work is that consideration of the consequences of a game presented in relation to seven potential phases to match status can point to a novel approach to analysis.

#10 Relationships Among Circuit Training, Small-Sided and Mini Goal Games, and Competition in Professional Soccer Players: A Comparison of On-Field Integrated Training Routines
Reference: J Strength Cond Res. 2019 Jul;33(7):1887-1896. doi: 10.1519/JSC.0000000000002804.
Authors: Giménez JV, Gomez MA
Summary: The aim of this study was to investigate and compare different physical variables and load indicators of 2 small-sided game (SSG) formats and ball circuit training (CT). Fourteen professional players participated in 3 training routines using a similar occupied area per player (90 m). The CT, SSGs, and mini goal games (MGs) consisted of 8 repetitions of 4-minute game play, interspersed by 2 minutes of active recovery, and data were compared with the first 32 minutes of 2 competitive match simulations (MS). All movement patterns from walking to sprinting were recorded using 10-Hz global positioning system devices, whereas player perception of exertion was recorded after trial using a visual analogue scale. Practical differences among the 3 drills and MS were analyzed using magnitude-based inferences. The results suggested that the training routines did not exactly replicate the movement patterns of a competitive match. Furthermore, this study provides evidence that if high-intensity play is preferred, then SSGs should be emphasized (because they provide more total accelerations compared with the other drills; most likely effects). Moreover, the CT showed lower load and distance covered (m) than the MGs and SSGs. In conclusion, these drills may be useful for competition and impact microcycles (i.e., intermittent efforts with accelerations, decelerations, and walking actions) to achieve the specific adaptations of high-intensity efforts.

#11 Are two different speed endurance training protocols able to affect the concentration of serum cortisol in response to a shuttle run test in soccer players?
Reference: Res Sports Med. 2019 Jun 25:1-9. doi: 10.1080/15438627.2019.1635131. [Epub ahead of print]
Authors: Vitale JA, Povìa V, Belli E, Lombardi G, Banfi G, La Torre A
Summary: Soccer involves multiple high-intensity physical, technical and tactical actions; as result of this, soccer training must include high-intensity exercises, which can act as a stimulus to the hypothalamus pituitary-adrenal axis, resulting in a significant increase in circulating cortisol levels. This study examined the effect of 4 weeks of Speed Endurance Maintenance (SEM) and Speed Endurance Production (SEP) on the serum cortisol concentration in response to a 5-meter multiple shuttle run test (5-m MST) in young elite soccer players. Fifteen soccer players were divided to SEM (n = 7) or SEP (n = 8) training group. Blood drawings were performed four times: before and after the 5-m MST at baseline (T1a, T1b) and at follow-up (T2a, T2b). Both training regimes determined a cortisol secretion following the 5-m MST at both baseline and follow-up. Data on delta values highlighted that SEP had greater values than SEM at baseline and registered a significant decrease at the follow-up. This difference is probably due to the lack of specific speed endurance training for players of SEP group prior to the beginning of the protocol. The physiological mechanisms behind the observed biological differences should be deeply investigated.

#12 Design and evaluation of sound-based electronic football soccer training system for visually impaired athletes
Reference: Biomed Eng Online. 2019 Jun 24;18(1):76. doi: 10.1186/s12938-019-0695-5.
Authors: Yandun F, Auat Cheein FA, Lorca D, Acevedo O, Auat Cheein C
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Summary: Several countries encourage the practice of football for rehabilitation and social inclusion purposes. For visually impaired people, football is purely sound-based, where the ball and the players are constantly emitting sounds for localization purposes in the field. However, the task of shooting the ball requires of a non-visually impaired extra person, behind the goal (known as caller), whom is punching the four corner of such goal to help the athletes. The presence of the caller restricts the self-sufficiency of the players. This work addresses such problem, by presenting a goal for visually impaired players with the aim of enhancing their self-sufficiency. The electronic goal is designed with four functionalities for training purposes, by returning sound-based feedback of its position and the places where the ball has impacted. The system is validated with seven volunteers from Chilean Football Soccer National Team. A questionnaire was answered by the players before and after the tests to statically validate the proposed device. The presented system is portable and designed following a modular criterion suitable for visually impaired people self-assembling. From a test of 350 shootings, the electronic goal showed to enhance the shooting assertiveness from 82 to 92%, and the accuracy from 20 to 56% compared to the traditional caller. The electronic goal showed to enhance the self-sufficiency of athletes, by improving their assertiveness in shooting training. Nevertheless, and according to the responses to the questionnaires, the system needs improvements in its portability and handling.






Latest research in football - week 24 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Assessment of a Nutrition Intervention on the Nutrition Knowledge, of Adolescent Soccer Academy Players
Reference: Curr Dev Nutr. 2019 Jun 13;3(Suppl 1). pii: nzz050.P16-044-19. doi: 10.1093/cdn/nzz050.P16-044-19. eCollection 2019 Jun.
Authors: Ray S, Mounce CD, Gonzalez-Rodenas J, Prieto MS, Brannan R
Summary: National surveys found that adolescents in America often fail to meet dietary recommendations probably due to lack of nutrition knowledge, giving rise to chronic diseases such as obesity, coronary heart diseases and type 2 diabetes. Knowledge about sports nutrition is considered essential for adolescent athletes to have healthy eating habits. It would help maximize their performance. The aim of the study was to assess the nutrition knowledge of adolescent soccer players pre and post a nutrition education intervention. A study was conducted on the youth academy level soccer players (n = 21) from three age groups (U19, U17, U15), to determine their nutrition knowledge using a validated Nutrition Knowledge Questionnaire. From the completed questionnaire, on factors like energy refueling, hydration, supplements and protein, a knowledge score was calculated for each athlete ranging from 0 (0%) to 16 (100%). The players participated in a nutrition education intervention for 5 months, consisting of monthly nutritional education newsletters, electronic handouts and one-hour nutrition lesson in the form of jeopardy game and nutrition education workshop for the players and their parents. Following the intervention, they filled out the same questionnaire again. From their responses, pre- and post-intervention, we found that at baseline, nutrition knowledge was highest in the U19 team as 44% of the responses were correct, lesser for the U17 team (25%) and least for the U15 team (6%). However, the intervention only produced a 6% increase in nutrition knowledge in the U19 while the intervention produced a 19% increase in the U17 team and a 44% increase in the U15 team. There was significant improvement in the category under supplements which asked whether it was better to get vitamins and minerals from supplements than from foods (P = 0.002). There was no significant difference in improvement of protein knowledge after the intervention in any group. The study shows that the nutrition education intervention was most effective for the younger players. Overall, more nutrition education, especially in the area of proteins, would be required for these players to increase their nutrition knowledge so that they know the type of food they should select and understand the importance of healthy eating.

#2 Evolution of technical activity in various playing positions, in relation to match outcomes in professional soccer
Reference: Biol Sport. 2019 Jun;36(2):181-189. doi: 10.5114/biolsport.2019.83958. Epub 2019 Apr 25.
Authors: Konefał M, Chmura P, Zając T, Chmura J, Kowalczuk E, Andrzejewski M
Summary: The study presented below aimed to examine the position-specific evolution of technical activity among soccer players and how it is related to match outcomes over three consecutive domestic seasons in Germany's Bundesliga. The research was based on a sample of 13,032 individual match observations of 556 soccer players during the 2014/2015, 2015/2016 and 2016/2017 seasons. These players were classified into five positional roles: central defenders (CD), full-backs (FB), central midfielders (CM), wide midfielders (WM) and forwards (F). The activity of the players was analysed using the Impire AG motion analysis system. Our study indicates that over the course of the three seasons: 1) the total numbers of shots by CMs decreased in the case of won or drawn matches; 2) the number of passes by CD players increased in matches won, and by CM and WM players in matches won, drawn and lost, whereas percentage pass accuracy increased at the CM position in won and drawn matches; 3) players at each position engaged in a substantially smaller number of duels, no matter what the match outcome, while the percentage of encounters won in subsequent seasons decreased among CD, and increased among WM in matches won and at F positions in both won and drawn matches. This research clearly shows that the evolution of technique among professional soccer players is heading in the direction of increased accuracy, with a simultaneous stabilisation of, or even a decline in, the number of activities engaged in.

#3 Influence of warm-up duration on perceived exertion and subsequent physical performance of soccer players
Reference: Biol Sport. 2019 Jun;36(2):125-131. doi: 10.5114/biolsport.2019.81114. Epub 2019 Jan 11.
Authors: Yanci J, Iturri J, Castillo D, Pardeiro M, Nakamura FY
Summary: The aim of this study was to analyse the effects of three warm-up protocols with different durations in semiprofessional soccer players. Fifteen semi-professional soccer players performed three warm-up protocols (Wup25min: 25 min, Wup15min: 15 min and Wup8min: 8 min duration) on three different days. Before (pre-test) and after (post-test) each warm-up protocol, the players' physical performance (sprint, vertical jump and change of direction) was evaluated and all the players were asked to respond to the subjective scale of readiness to play a match. Also, after completing each warm-up protocol, all players responded to the rating of perceived exertion (RPE) scale. Although all protocols significantly improved the feeling of players being prepared to play the game (p<0.05 or p<0.01), after performing the Wup25min protocol the players performed worse in the 10 m sprint (p<0.01) and in the 20 m sprint (p<0.05). However, the Wup8min protocol significantly improved performance in both the 10 m sprint (p<0.05) and the 20 m sprint (p<0.05). In addition, with the Wup25min protocol players stated a higher perceived exertion (RPE) (p < 0.05) than in the Wup15min and Wup8min protocols. The Wup8min protocol was the only one that improved the acceleration ability of the soccer players in this study.

#4 Sprint force-velocity profiles in soccer players: impact of sex and playing level
Reference: Sports Biomech. 2019 Jun 21:1-11. doi: 10.1080/14763141.2019.1618900. [Epub ahead of print]
Authors: Devismes M, Aeles J, Philips J, Vanwanseele B
Summary: This study aimed to assess potential differences in force-velocity (Fv) profiles in both male and female soccer players of different playing levels. One hundred sixty three soccer players (63 women and 100 men) competing from the Regional to the National Belgian league were recruited. The participants performed two maximal 60-m sprints monitored via a 312 Hz laser. For each participant, the theoretical maximal force (F0) and velocity (v0), maximal power (Pmax), maximal ratio of force (RF) and the slope of the Fv profile (Sfv) were computed. Male players in the highest competition level showed higher values for all the Fv variables compared to lower level groups (Effect size range: 1.01-1.97). Higher Pmax and v0 were observed in the female players of highest competition level compared to all other groups (ES range: 1.09-1.48). Female players showed more negative Sfv than male players (ES = 1.11), which suggests that male players' Fv profile is more velocity-oriented compared to female players. This study shows that the determinants of sprint performance increase with soccer playing level in both men and women, but that the contribution of each variable varies with sex.

#5 Vague Posterior Knee Discomfort in a Soccer Player: A Case Report
Reference: Am J Phys Med Rehabil. 2019 Jun 17. doi: 10.1097/PHM.0000000000001248. [Epub ahead of print]
Authors: Schroeder A, Onishi K
Summary: A 24-year-old male soccer player presented with a 7-year history of left posterior knee "looseness." Evaluation 7 years ago, at the time of initial injury, revealed atraumatic ACL and PCL sprains. On re-presentation, the patient described the pain as a constant, dull ache, 3/10, but his biggest complaint was this feeling of "instability" and "looseness" where his knee would "buckle" 3-4 times a week. Physical exam was positive for grade 1 posterior drawer and grade 1 posterior sag signs. Reverse KT-1000 testing showed a 3 mm side-to-side difference. Sonographic evaluation confirmed MRI findings of PCL laxity and buckling and a small cystic lesion abutting the posteromedial margin of the distal 1/3 of the PCL. After a trial of physical therapy, the patient elected to undergo experimental injection of dextrose hyperosmolar solution. This resulted in resolution of the cyst and reverse KT-1000 measurements improved to a side-to-side difference of 1 mm. The patient's subjective feeling of "looseness" and "instability" resolved by 7 weeks.

#6 Physical performance metrics in elite soccer: do power and acceleration metrics provide insight into positional demands and match-related fatigue in the 4-3-3 system?
Reference: J Sports Med Phys Fitness. 2019 Jun 19. doi: 10.23736/S0022-4707.19.09772-X. [Epub ahead of print]
Authors: Filetti C, Ruscello B, Ascenzi G, Di Mascio M, D'ottavio S
Summary: The aim of this study was to quantify power and acceleration metrics in elite soccer matches to gain an insight into positional demands and match-related fatigue patterns. Elite players (n = 212, observations = 522) were analysed during 50 matches of the Italian Serie A using a semi-automatic tracking system (K-Sport, Montelabbate, PU, Italy - Stats, Leeds, UK) during the 2015/16 season. A principal component analysis (PCA) was performed to find the latent variables that better explain the huge amount of data collected; an ANOVA was performed to find differences among positional roles and a mixed factorial analysis of mixed data (FAMD) was carried out to investigate the patterns of fatigue over time. Power and Acceleration were defined as the latent variables out of the 19 investigated that provided most of the variance (90.39%); significant differences among roles were found (p<0.05; Effect Size (ES) as ω2>0.14) and significant patterns of fatigue (p<0.05) with a moderate to large ES were observed over time in some of the key performance indicators. The data demonstrate that there are implications for developing power and acceleration in training sessions and assessing these components during a game. With the introduction of 'live streaming' of GPS data, the movement patterns could be observed in real time, and interchanges could be made before the onset of fatigue and before evident reductions in performance might be observed.

#7 The Effect of a Four-Month Training Program on Body Fat and Pulmonary Parameters of Young Soccer Players
Reference: Iran J Public Health. 2019 Feb;48(2):353-354.
Authors: Sermaxhaj S
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#8 Relation of injuries and psychological symptoms in amateur soccer players
Reference: BMJ Open Sport Exerc Med. 2019 Apr 24;5(1):e000522. doi: 10.1136/bmjsem-2019-000522. eCollection 2019.
Authors: Jansen P, Lehmann J, Fellner B, Huppertz G, Loose O, Achenbach L, Krutsch W
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Summary: The first main goal of this study was to investigate the prevalence of depression and anxiety as well as self-compassion in a heterogeneous sample of male amateur soccer players. The second main goal of this study was the examination of the relationship between injuries and psychological factors in amateur soccer players. Players were recruited from German amateur soccer clubs of the fourth to seventh league. 419 soccer players with the mean age of 22.88 years participated in the psychological and the injury assessment at the beginning of the season and at the end, 9 months later. For the psychological assessment, depression and anxiety rate as well as self-compassion was analysed. Furthermore, the frequencies of injuries were registered. The results showed that players of the highest amateur league, the fourth league in German soccer, showed significantly higher anxiety values than players from a lower league (p=0.013). There were no differences in depression values dependent on the league. Furthermore, players who suffered from an injury before the start of the season demonstrated higher anxiety values (p=0.027). This result was independent of the respective league. The results of this study demonstrate that even in higher amateur soccer the anxiety level of the players varies between soccer players of different leagues. Because an injury before the start of the season influenced the anxiety level, a psychological treatment during injury should be considered.

#9 Professional soccer player with an in-game ankle injury
Reference: Skeletal Radiol. 2019 Jun 16. doi: 10.1007/s00256-019-03253-6. [Epub ahead of print]
Authors: Iqbal A, McLoughlin E, Botchu R, James SL
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#10 Comparison of knee sonography and pressure pain threshold after anterior cruciate ligament reconstruction with quadriceps tendon versus hamstring tendon autografts in soccer players
Reference: Acta Orthop Traumatol Turc. 2019 Jun 12. pii: S1017-995X(18)30300-6. doi: 10.1016/j.aott.2019.04.012. [Epub ahead of print]
Authors: Martin-Alguacil JL, Arroyo-Morales M, Martin-Gómez JL, Lozano-Lozano M, Galiano-Castillo N, Cantarero-Villanueva I
Summary: The aim of this study was to compare the pressure pain threshold and muscle architecture after an anatomic single bundle reconstruction with quadriceps tendon and hamstring tendon autografts of the anterior cruciate ligament in competitive soccer players. We hypothesized that both procedures will obtain similar outcomes. Fifty-one participants were enrolled in this secondary analysis of a randomized controlled trial and were categorised into two groups: quadriceps tendon (QT) group (23 men and 3 women; mean age 18.7 ± 3.6; BMI 23.0 ± 2.2) or hamstring tendon (HT) group (16 men and 9 women; mean age 19.2 ± 3.6 BMI 23.5 ± 3.5). Both groups followed the same rehabilitation staged protocol. Pressure pain threshold (PPT), as a measure of perceived pain, was obtained in several points of quadriceps and hamstring muscles. Ultrasound imaging measurements were obtained in quadriceps tendon and knee cartilage thickness. Four measurements were taken in this study: baseline, 1, 3, 6, and 12 months after the anterior cruciate ligament (ACL) reconstruction. The analysis of PPT did not find significant differences in both groups × interaction time in the points evaluated: epicondyle (QT = 421.1 ± 184.1 vs HT = 384.7 ± 154.1 kPa), vastus lateralis (QT = 576.2 ± 221.3 vs HT = 560.1 ± 167.7 kPa), vastus medialis (QT = 544.7 ± 198.8 vs HT = 541.1.1 ± 181.77 kPa), patellar tendon (QT = 626.3 ± 221.1 vs HT = 665.0 ± 205.5 kPa), QT (QT = 651.1 ± 276.9 vs HT = 660.0 ± 195.2 kPa). (QT = 667.8 ± 284.7 vs HT = 648.2 ± 193.4 kPa) injured knee (all P > 0.05). The results of ultrasound imaging did not show significant differences in both groups × interaction time in the thickness of the QT (QT = 9.9 ± 2.4 vs HT = 9.4 ± 1.7 kPa) and patellar cartilage (QT = 3.2 ± 0.6 vs HT = 3.2 ± 0.4 kPa) (P > 0.05). A QT autograft produces similar results to a HT autograft in ACL reconstructions in terms of pressure pain threshold and ultrasound muscle architecture during the 1-year follow-up.

#11 Positional demands for various-sided games with goalkeepers according to the most demanding passages of match play in football
Reference: Biol Sport. 2019 Jun;36(2):171-180. doi: 10.5114/biolsport.2019.83507. Epub 2019 Mar 14.
Authors: Martin-Garcia A, Castellano J, Diaz AG, Cos F, Casamichana D
Summary: The main aim was to determine the differences between four training games and competitive matches (CM) according to position and compared to the most demanding passages (MDP) of competitive match play. Global Positioning System data were obtained from 21 football players belonging to the reserve squad of a Spanish La Liga club during the 2015/16 season. The training games were small-sided games (SSGs) with 5 and 6 and large-sided games with 9 and 10 outfield players per team. The players were categorized based on positional groups: full back (FB), central defender (CD), midfielder (MF), offensive midfielder (OMF), and forward (FW). The variables recorded were the distance covered (DIS), DIS at high speed (HSR; >19.8 km·h-1), DIS at sprint (SPR; >25.2 km·h-1), high metabolic load distance (HMLD; >25.5 W·kg-1) all in m·min-1, average metabolic power (AMP; W·kg-1) and number of high-intensity accelerations (ACC; >3 m·s-2) and decelerations (DEC; <-3 m·s-2), both in n·min-1. The MDP was analysed using a rolling average method for AMP as a criterion variable, where maximal values were calculated for time windows of 5 and 10 minutes of CM and after that compared with the training game formats. As the SSG format increases, all the rest of the variables increase and the number of cases with significant interposition differences also increases (effect size [ES]: DIS: 0.7-2.2; HSR: 0.7-2.1; SPR: 0.8-1.4; HMLD: 0.9-2.0; AMP: 0.8-1.9; ACC: 0.8-1.7; DEC: 0.5-1.7). The large-sided game 10v10 + 2 goalkeepers over-stimulates sprint values relative to MDP (all: 121.0% of MDP, ES=0.5-1.8). This study provides useful information for coaching staff on the heightened impact of different training game formats on physical load, considering positional differences in relation to the MDP of competitive match play.

#12 Relative pitch area plays an important role in movement pattern and intensity in recreational male football
Reference: Biol Sport. 2019 Jun;36(2):119-124. doi: 10.5114/biolsport.2019.81113. Epub 2019 Jan 11.
Authors: Pantelić S, Rađa A, Erceg M, Milanović Z, Trajković N, Stojanović E, Krustrup P, Randers MB
Summary: Recreational football has been shown to be an effective health-promoting activity, but it is still unclear how changes in game formats affect external and internal load. The aim of this study was therefore to evaluate the effect of area per player in recreational small-sided football games. Ten recreational active male football participants (mean±standard deviation, age: 20.1±1.1 years; height: 182.2±7.4 cm; body mass: 75.9±9.8 kg) completed two sessions comprising 2x20 min of 5v5 football with 80 and 60 m2 per player, during which heart rate (HR) and movement pattern were measured. In 80 m2, mean HR (167±9 vs. 160±10 b.p.m., P<0.001, ES=0.70) and peak HR (192±8 vs. 188±9 b.p.m., P=0.041, ES=0.50) were significantly higher than in 60 m2. Percentage playing time with HR >90%HRpeak was higher in 80 m2 than 60 m2 (45±14 vs. 29±16%, P=0.004, ES=1.07). Moreover, a higher number of sprints (8.0±4.8 vs. 3.0±1.3, P=0.014, ES=1.41) and a greater distance in the highest speed zones (>13, >16 and >20 km·h1) were covered in 80 m2 than 60 m2. Peak running speed was also higher in 80 m2 (24.3±1.7 vs. 22.3±1.4 km·h-1, P=0.011, ES=1.27), whereas no statistically significant differences were found in total distance covered, player load, or the acceleration-deceleration profiles. In conclusion, the internal and external loading was higher for recreationally active male football players when playing on a pitch with 80 m2 area per player compared to 60 m2.





Latest research in football - week 23 - 2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:


#1 Fundamental Motor Skills Mediate the Relationship Between Physical Fitness and Soccer-Specific Motor Skills in Young Soccer Players
Reference: Front Physiol. 2019 May 28;10:596. doi: 10.3389/fphys.2019.00596. eCollection 2019.
Authors: Kokstejn J, Musalek M, Wolanski P, Murawska-Cialowicz E, Stastny P
Summary: Fundamental motor skills (FMS) are the basic elements of more complex sport-specific skills and should be mastered at the end of early childhood; however, the relationship between FMS and sport-specific skills has not yet been verified in prepubertal soccer players. Therefore, the aim of this study was to determine the role of FMS in the process of acquiring soccer-specific motor skills (measured using speed dribbling) with regard to physical fitness and biological maturation. Forty male soccer players (11.5 ± 0.3 years of age) at the highest performance level participated in the study. The test of Gross Motor Development - second edition and Unifittest 6-60 were used to assess FMS and physical fitness, respectively. The role of FMS in a complex theoretical model with the relationships between physical fitness, biological maturation and speed dribbling was analyzed by multiple regression path analyses (MRPA). Moderate to strong correlations were found between FMS, physical fitness, and speed dribbling (r = 0.56-0.66). Biological maturation did not appear to be a significant predictor of physical fitness or speed dribbling. The MRPA model using FMS as mediator variable between physical fitness and speed dribbling showed a significant indirect effect (standard estimation = -0.31, p = 0.001; R 2 = 0.25). However, the direct correlation between physical fitness and speed dribbling was non-significant. Our results showed that FMS significantly strengthened the influence of physical fitness on the performance of speed dribbling, a soccer-specific motor skill, and thus play an important role in the process of acquiring sport-specific motor skills in prepubertal soccer players. When considering the long-term training process, especially during childhood and before puberty, a wide range of FMS activities should be applied for better and possibly faster acquisition of soccer-specific motor skills.

#2 Tart Cherry Juice: No Effect on Muscle Function Loss or Muscle Soreness in Professional Soccer Players After a Match
Reference: Int J Sports Physiol Perform. 2019 Jun 12:1-21. doi: 10.1123/ijspp.2019-0221. [Epub ahead of print]
Authors: Abbott W, Brashill C, Brett A, Clifford T
Summary: The purpose was to investigate the effects of tart cherry juice (TCJ) on recovery from a soccer match in professional players. In a double-blind, placebo-controlled, crossover design, 10 male professional soccer players from the reserve team of an English Premier League Club (age 19 ± 1 y, height 1.8 ± 0.6 m, body mass 77.3 ± 6.4 kg) consumed 2 × 30-mL servings of TCJ or an isocaloric cherry-flavored control drink (CON) before and after a 90-min match, and 12 and 36 h after the match. Muscle function (countermovement jump-height [CMJ], reactive strength index [RSI]), subjective well-being, and subjective muscle soreness (MS) were measured before and 12, 36, and 60 h after each match. CMJ height was similarly reduced in the days after the match after TCJ and CON supplementation, with the greatest loss occurring at 12 h postmatch (-5.9% ± 3.1% vs -5.4% ± 2.9% of baseline values, respectively; P = .966, ηp2 = .010). Decrements in RSI were also greatest at 12 h postmatch (TCJ -9.4% ± 8.4% vs CON -13.9% ± 4.8% of baseline values), but no group differences were observed at any time point (P = .097, ηp2 = .205). MS increased 12-60 h postmatch in both groups, peaking at 12 h postmatch (TCJ 122 ± 27 mm vs CON 119 ± 22 mm), but no group differences were observed (P = .808, ηp2 = .024). No interaction effects were observed for subjective well-being (P = .874, ηp2 = .025). Tart cherry juice did not hasten recovery after a soccer match in professional players. These findings bring into question the use of TCJ as a recovery aid in professional soccer players.

#3 Macronutrient Intake in Soccer Players-A Meta-Analysis
Reference: Nutrients. 2019 Jun 9;11(6). pii: E1305. doi: 10.3390/nu11061305.
Authors: Steffl M, Kinkorova I, Kokstejn J, Petr M
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Summary: The nutrition of soccer players is an important topic and its knowledge may help to increase the quality of this popular game and prevent possible health problems and injuries in players. This meta-analysis aims to estimate the current dietary trends of three basic macronutrients in junior and senior soccer players during the first two decades of the 21st century. We analyzed data from 647 junior players (mean age 10.0-19.3) from 27 groups, and 277 senior (mean age 20.7-27.1) players from 8 groups from altogether 21 papers in this meta-analysis. Weighted averages were calculated for each macronutrients. Protein intake is higher than recommended in both juniors, 1.9 95% confidence interval (CI) 1.8-2.0 g/kg/day, and seniors 1.8 95% CI 1.6-2.0 g/kg/day. However, carbohydrate intake is still below the recommended values in both groups (5.7 95% CI 5.5-5.9 g/kg/day in junior and 4.7 95% CI 4.3-5.0 g/kg/day in senior players). The proportion of fat as total energy intake is in concordance with the recommendations (31.5 95% CI 32.0-35.9% in junior and 33.1 95% CI 29.9-36.2% in senior players). In particular, due to possible health complications, the small carbohydrate intake should be alarming for coaches, nutritional experts, and parents.

#4 How anterior pelvic tilt affects the lower extremity kinematics during the late swing phase in soccer players while running: A time series analysis
Reference: Hum Mov Sci. 2019 Jun 5;66:459-466. doi: 10.1016/j.humov.2019.06.001. [Epub ahead of print]
Authors: Alizadeh S, Mattes K
Summary: Anterior pelvic tilt has been proposed to predispose the hamstring in soccer players to injury at the late swing phase during a sprint, however the mechanism on how the changes in the alignment would affect the kinematics are still unclear. Thirty-four male amateur soccer players were recruited for this study. Pelvic tilt was measured using the DIERS Formetric 4D. Lower extremity angles were recorded using an 8-camera Vicon motion capture system at 200 Hz while the athlete performed a high speed run on a motorised treadmill. Late swing phase was extracted from 5 running cycle which were later analysed using statistical parametric mapping (SPM). The results show that the increase of anterior pelvic tilt angle was significantly correlated with hip (r = -0.421 to -0.462, p = 0.015) and knee flexion (r = -0.424 to -0.472, p = 0.026) values. No other correlation was found between the anterior pelvic tilt and the angles at the coronal plane. By using time series analysis it was shown that the anterior pelvic tilt measured in a standing position would affect the adjacent segments' kinematics while running as suggested in the kinetic chain theory; which would potentially predispose the soccer athletes to hamstring injury by maintaining knee extension.

#5 Gaining or Losing Team Ball Possession: The Dynamics of Momentum Perception and Strategic Choice in Football Coaches
Reference: Front Psychol. 2019 May 28;10:1019. doi: 10.3389/fpsyg.2019.01019. eCollection 2019.
Authors: Briki W, Zoudji B
Summary: Grounded in the dynamical systems approach, the present research examined the influence of team ball possession (TBP) in soccer on coaches' perceived psychological momentum (PM) and strategic choice (i.e., game-based "stick" vs. "switch" choices) during a simulated match. Experienced soccer coaches imagined being the coach of the team involved in a highly important match that was displayed on a wall in a lecture hall. The match scenario was manipulated so that the coach was exposed to either a positive momentum sequence (i.e., ascending scenario of TBP) or a negative momentum sequence (i.e., descending scenario of TBP). Results revealed that positive (or negative) momentum sequence increased (or decreased) perceived PM and increased stick (or switch) choices. Perceived PM globally evolved linearly, while strategic choice displayed a dynamical pattern of "critical boundary" (thus showing a nonlinear change). Nonetheless, both variables displayed asymmetrical effects, in the sense that: (1) the strength of positive PM appeared to be easier to decrease than to increase; and (2) the greater the positive PM (or the negative PM), the lesser (or the greater) the coaches' tendency to make a change in the organization of their teams. This investigation evidences that TBP can powerfully influence coaches' perceptions and strategic decisions, and that coaches are more likely to be sensitive to negative events than to equivalent positive events.

#6 Time before return to play for the most common injuries in professional football: a 16-year follow-up of the UEFA Elite Club Injury Study
Reference: Br J Sports Med. 2019 Jun 10. pii: bjsports-2019-100666. doi: 10.1136/bjsports-2019-100666. [Epub ahead of print]
Authors: Ekstrand J, Krutsch W, Spreco A, van Zoest W, Roberts C, Meyer T, Bengtsson H
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Summary: The objective was to describe the typical duration of absence following the most common injury diagnoses in professional football. Injuries were registered by medical staff members of football clubs participating in the Union of European Football Association Elite Club Injury Study. Duration of absence due to an injury was defined by the number of days that passed between the date of the injury occurrence and the date when the medical team allowed the player to return to full participation. In total, 22 942 injuries registered during 494 team-seasons were included in the study. The 31 most common injury diagnoses constituted a total of 78 % of all reported injuries. Most of these injuries were either mild (leading to a median absence of 7 days or less, 6440 cases = 42%) or moderate (median absence: 7-28 days, 56% = 8518 cases) while only few (2% = 311 cases) were severe (median absence of >28 days). The mean duration of absence from training and competition was significantly different (p < 0.05) between index injuries and re-injuries for six diagnoses (Achilles tendon pain, calf muscle injury, groin adductor pain, hamstring muscle injuries and quadriceps muscle injury) with longer absence following re-injuries for all six diagnoses. The majority of all time loss due to injuries in professional football stems from injuries with an individual absence of up to 4 weeks. This article can provide guidelines for expected time away from training and competition for the most common injury types as well as for its realistic range.

#7 Keep Your Head Up-Correlation between Visual Exploration Frequency, Passing Percentage and Turnover Rate in Elite Football Midfielders
Reference: Sports (Basel). 2019 Jun 6;7(6). pii: E139. doi: 10.3390/sports7060139.
Authors: Phatak A, Gruber M
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Summary: Statistical analysis of real in-game situations plays an increasing role in talent identification and player recruitment across team sports. Recently, visual exploration frequency (VEF) in football has been discussed as being one of the important performance-determining parameters. However, until now, VEF has been studied almost exclusively in laboratory settings. Moreover, the VEF of individuals has not been correlated with performance parameters in a statistically significant number of top-level players. Thus, the objective of the present study was to examine the relationship between VEF and individual performance parameters in elite football midfielders. Thirty-five midfielders participating in the Euro 2016 championship were analyzed using game video. Their VEF was categorized into scans, transition scans, and total scans. Linear regression analysis was used to correlate the three different VEF parameters with the passing percentage and the turnover rate for individual players. The linear regression showed significant positive correlations between scan rate (p = 0.033, R 2 = 3.0%) and total scan rate (p = 0.015, R 2 = 4.0%) and passing percentage but not between transition scan rate and passing percentage (p = 0.074). There was a significant negative correlation between transition scan rate and turnover rate (p = 0.023, R 2 = 3.5%) but not between total scan rate (p = 0.857) or scan rate (p = 0.817) and turnover rate. In conclusion, the present study shows that players with a higher VEF may complete more passes and cause fewer turnovers. VEF explains up to 4% of variance in pass completion and turnover rate and thus should be considered as one of the factors that can help to evaluate players and identify talents as well as to tailor training interventions to the needs of midfielders up to the highest level of professional football.

#8 Tackling Similarity Search for Soccer Match Analysis: Multimodal Distance Measure and Interactive Query Definition
Reference: IEEE Comput Graph Appl. 2019 Jun 12. doi: 10.1109/MCG.2019.2922224. [Epub ahead of print]
Authors: Stein M, Janetzko H, Keim DA, Schreck T.
Summary: Analysts and coaches in soccer sports need to investigate large sets of past matches of opposing teams in short time to prepare their teams for upcoming matches. Thus, they need appropriate methods and systems supporting them in searching for soccer moves for comparison and explanation. For the search of similar soccer moves, established distance and similarity measures typically only take spatio-temporal features like shape and speed of movement into account. However, movement in invasive team sports such as soccer, includes much more than just a sequence of spatial locations. We propose an enhanced similarity measure integrating spatial, player, event as well as high level context such as pressure into the process of similarity search. We present a visual search system supporting analysts in interactively identifying similar contextual enhanced soccer moves in a dataset containing more than 60 soccer matches. Our approach is evaluated by several expert studies. The results of the evaluation reveal the large potential of enhanced similarity measures in the future.

#9 Inter-relationship between sleep quality, insomnia and sleep disorders in professional soccer players
Reference: BMJ Open Sport Exerc Med. 2019 Apr 24;5(1):e000498. doi: 10.1136/bmjsem-2018-000498. eCollection 2019.
Authors: Khalladi K, Farooq A, Souissi S, Herrera CP, Chamari K, Taylor L, El Massioui F
Summary: Insufficient sleep duration and quality has negative effects on athletic performance, injury susceptibility and athlete development. This study aimed to assess the sleep characteristics of professional Qatar Stars League (QSL) soccer players. In a cross-sectional study, QSL players (n=111; 23.7±4.8 years) completed three questionnaires to screen sleep disorders: (1) Pittsburgh Sleep Quality Index (PSQI), (2) Insomnia Severity Index (ISI) and (3) Epworth Sleepiness Scale (ESS). Poor sleep quality was defined as PSQI≥5, excessive daytime sleepiness was defined by ESS>8 and insomnia was defined as ISI≥11. The prevalence of poor sleep quality (PSQI≥5) was 68.5%, with subthreshold insomnia (ISI≥11) 27.0% and daytime sleepiness 22.5% (ESS>8). Sleep quality was positively associated with insomnia (r=0.42, p<0.001) and daytime sleepiness (r=0.23, p=0.018). Age, anthropometry, body composition and ethnicity were not associated with any of the reported sleep quality parameters. The prevalence of poor sleep quality (68.5%) reported should concern practitioners. Increasing awareness of the importance of sleep relative to athletic performance, recovery, injury and illness appears prudent. Further, regular qualitative/quantitative sleep monitoring may help target subsequent evidence-informed interventions to improve sleep in those demonstrating undesirable sleep traits.

#10 Competitive Psychological Disposition and Perception of Performance in Young Female Soccer Players
Reference: Front Psychol. 2019 May 22;10:1168. doi: 10.3389/fpsyg.2019.01168. eCollection 2019.
Authors: Olmedilla A, Ruiz-Barquín R, Ponseti FJ, Robles-Palazón FJ, García-Mas A
Summary: The athletes' psychological disposition is a factor that is increasingly considered by researchers as a key to sports performance, even as a mediator between the physical, technical and tactical abilities of the athlete and their competitive performance, thus acquiring great relevance in training and in sports performance. The purpose of this study is to analyze the psychological characteristics of young soccer players and their relation to their performance perception, made both by the player herself and by their coaches. The sample is composed of 108 women (M age = 15.53, SD age = 1.05), with ages between 13 and 17 years (13 years, n = 1, 14 years, n = 18, 15 years, n = 36, 16 years, n = 29, 17 years, n = 24), and with a sport practice experience of 7.27 years on average (SD = 2.64). For to address this aim, we used the Psychological Characteristics related to the Sport Performance Questionnaire (CPRD) and the Psychological Skills Inventory for Sports (PSIS). In addition, regarding the evaluation of performance perception, an ad hoc short questionnaire was created, composed by one question addressed to the player and one directed to the coach. The results indicate that the group of players of the under-16 category obtained higher scores in all the psychological dimensions than the U-18 players, showing significant differences in Team Cohesion (p < 0.048). Regarding the degree of congruence between the player's psychological features, and the player's and coach's performance perceptions, the results show statistically significant and negative correlations between the Team Cohesion factor and the athlete's own outcome perception for the match #1 (rxy = -0.479; p < 0.001), and match #2 (rxy = -0.402; p < 0.01). The results of this study may contribute to establish the differences between different constellations of psychological characteristics according to the categories of competition and their relationship with the perception of performance. This knowledge can be used by sports professionals: coaches, psychologists, physical educators, etc., in order to help athletes to reach their maximum performance.





Latest research in football - week 22 -2019

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 The Benefits of a Challenge Approach on Match Day: Investigating Cardiovascular Reactivity in Professional Academy Soccer Players
Reference: Eur J Sport Sci. 2019 Jun 6:1-32. doi: 10.1080/17461391.2019.1629179. [Epub ahead of print]
Authors: Dixon JG, Jones MV, Turner MJ
Summary: This study assessed physiological (cardiovascular) and psychological (confidence, control, and approach focus) data in professional academy soccer players prior to performance in competitive matches. A challenge state is characterised by an increase in cardiac output (CO), and a decrease in total peripheral vascular resistance (TPR). Data were collected from 37 participants, with 19 of these providing data on two separate occasions. Performance was measured using coach and player self-ratings. Challenge reactivity was positively, and significantly, associated with performance. Participants who demonstrated blunted cardiovascular (CV) responses performed significantly worse than participants who displayed either challenge or threat reactivity. There was mixed consistency in CV reactivity for those participants whose data were collected on more than one occasion, suggesting that some participants responded differently across the competitive matches. The association between self-report data and CV responses was weak. This study supports previous research demonstrating that challenge reactivity is associated with superior performance.

#2 First-Stance Phase Force Contributions to Acceleration Sprint Performance in Semi-Professional Soccer Players
Reference: Eur J Sport Sci. 2019 Jun 6:1-23. doi: 10.1080/17461391.2019.1629178. [Epub ahead of print]
Authors: Wdowski MM, Gittoes MJR
Summary: Sprint running is a key determinant of player performance in soccer that is typically assessed and monitored using temporal methods. The aim of this study was to examine the relationship between ground reaction force kinetics at the first step and sprint running performance in soccer players in order to enhance the development of training and assessment methods. Nineteen semi-professional soccer players participated (mean ± s: age 21.1 ± 1.9 years, body mass 79.4 ± 7.3 kg and stature 1.79 ± 0.06 m). The participants completed 20 m acceleration sprint runs as timing gates recorded split times between 0-5 m, 5-10 m, 10-15 m, 15-20 m and 0-20 m. A force plate captured vertical, anteroposterior and mediolateral ground reaction force data (1000 Hz) of the first right foot strike stance phase. Ground reaction force metrics, including peak anteroposterior propulsive force (r = 0.66 to 0.751; P = 0.000 to 0.002), peak vertical ground reaction force (r = 0.456 to 0.464; P = 0.045 to 0.05), average medial-lateral/anteroposterior orientation angle (r =-0.463; P = 0.023), and average anteroposterior/vertical orientation angle (r =-0.44; P = 0.03) were correlated with one or all split times between 0-5 m, 5-10 m, 10-15 m, 15-20 m and 0-20 m. Acceleration sprint running in soccer requires minimised mediolateral and increased anteroposterior loading in the stance phase. Multi-component ground reaction force measures of the first step in acceleration sprint runs are important for developing performance assessments, and understanding force application techniques employed by soccer players.

#3 Body composition, strength static and isokinetic, and bone health: comparative study between active adults and amateur soccer players
Reference: Einstein (Sao Paulo). 2019 May 30;17(3):eAO4419. doi: 10.31744/einstein_journal/2019AO4419. [Article in English, Portuguese]
Authors: Tavares ÓM, Duarte JP, Werneck AO, Costa DC, Sousa-E-Silva P, Martinho D, Luz LGO, Morouço P, Valente-Dos-Santos J, Soles-Gonçalves R, Conde J, Casanova JM, Coelho-E-Silva MJ
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Summary: The purpose was to compare tissue composition, total and regional bone mineral content and bone mineral density, static hand grip and knee joint isokinetic strength between amateur soccer players and Control Group. Cross-sectional study. Air displacement plethysmography was used to estimate body volume and, in turn, density. Body composition, bone mineral content and bone mineral density were assessed for the whole body and at standardized regions using dual energy X-ray absorptiometry. Static grip strength was assessed with an adjustable dynamometer, and peak torque derived from isokinetic strength dynamometer (concentric muscular knee actions at 60°/s). Magnitude of the differences between groups was examined using d-Cohen. Compared to healthy active adults, soccer players showed larger values of whole body bone mineral content (+651g; d=1.60; p<0.01). In addition, differences between groups were large for whole body bone mineral density (d=1.20 to 1.90; p<0.01): lumbar spine, i.e. L1-L4 (+19.4%), upper limbs (+8.6%) and lower limbs (+16.8%). Soccer players attained larger mean values in strength test given by static hand grip protocol (+5.6kg, d=0.99; p<0.01). Soccer adequately regulates body composition and is associated better bone health parameters (bone mineral content and density at whole-body and at particular sites exposed to mechanical loadings).

#4 Exploring simulated driving performance among varsity male soccer players
Reference: Traffic Inj Prev. 2019 Jun 5:1-6. doi: 10.1080/15389588.2019.1601715. [Epub ahead of print]
Authors: Tremblay M, Lavallière M, Albert WJ, Boudreau SR, Johnson MJ
Summary: It is documented that male athletes display riskier behaviors while driving (as well as in life in general) than female athletes and nonathletes. However, the literature has reported that athletes show better driving ability than nonathletes. This paradox between behaviors and abilities motivated the present study to further understand the collision risk of varsity athletes. The current study estimates the performance differences between varsity male soccer players and male undergraduate nonathletes on (1) a driving task and (2) three perceptual-cognitive tasks (associated with collision risk prediction; i.e., Useful Field of View [UFOV] test). Thirty-five male undergraduate students (15 varsity soccer players, 20 undergraduate nonathletes) took part in this study. Driving performance was assessed during 14 min of urban commuting using a driving simulator. While completing the simulated driving task and UFOV test, the physiological responses were monitored using an electrocardiograph (ECG) to document heart rate variability (HRV). Varsity soccer players showed more risky behaviors at the wheel compared to their nonathlete student peers. Varsity soccer players spent more time over the speed limit, committed more driving errors, and adopted fewer safe and legal behaviors. However, no difference was observed between both groups on driving skill variables (i.e., vehicle control, vehicle mobility, ecodriving). For subtests 1 and 2 of the UFOV (i.e., processing speed, divided attention), both groups performed identically (i.e., 17 ms). The nonathlete group tended to perform better on the selective attention task (i.e., subtest 3 of UFOV test; 63.2 ± 6.2 ms vs. 87.2 ± 10.7 ms, respectively; this difference was not significant, P = .76). Preventive driving measures should be enforced in this high-risk population to develop strategies for risk reduction in male team athletes.

#5 Methodological Issues in Soccer Talent Identification Research
Reference: Sports Med. 2019 Jun 3. doi: 10.1007/s40279-019-01113-w. [Epub ahead of print]
Authors: Bergkamp TLG, Niessen ASM, den Hartigh RJR, Frencken WGP, Meijer RR
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Summary: Talent identification research in soccer comprises the prediction of elite soccer performance. While many studies in this field have aimed to empirically relate performance characteristics to subsequent soccer success, a critical evaluation of the methodology of these studies has mostly been absent in the literature. In this position paper, we discuss advantages and limitations of the design, validity, and utility of current soccer talent identification research. Specifically, we draw on principles from selection psychology that can contribute to best practices in the context of making selection decisions across domains. Based on an extensive search of the soccer literature, we identify four methodological issues from this framework that are relevant for talent identification research, i.e. (1) the operationalization of criterion variables (the performance to be predicted) as performance levels; (2) the focus on isolated performance indicators as predictors of soccer performance; (3) the effects of range restriction on the predictive validity of predictors used in talent identification; and (4) the effect of the base rate on the utility of talent identification procedures. Based on these four issues, we highlight opportunities and challenges for future soccer talent identification studies that may contribute to developing evidence-based selection procedures. We suggest for future research to consider the use of individual soccer criterion measures, to adopt representative, high-fidelity predictors of soccer performance, and to take restriction of range and the base rate into account.

#6 Effects of plyometric jump training on the physical fitness of young male soccer players: Modulation of response by inter-set recovery interval and maturation status
Reference: J Sports Sci. 2019 Jun 3:1-8. doi: 10.1080/02640414.2019.1626049. [Epub ahead of print]
Authors: Ramirez-Campillo R, Alvarez C, Sanchez-Sanchez J, Slimani M, Gentil P, Chelly MS, Shephard RJ
Summary: The effects of plyometric jump training on the physical fitness of male youth (age = 10-17 years) soccer players was examined in relation to inter-set recovery intervals and the maturity of the players in a single-blind, randomized-and controlled crossover trial. Jumping tests and kicking velocities were measured before (T0), after a 6 week control period (T1), after 6 weeks of plyometrics (T2), after 6 weeks of wash-out (T3), and after a further 6 weeks of plyometrics (T4). Subjects were divided into pre- and post- peak-height-velocity (PHV) groups, and were randomly assigned to 30 s or 120 s inter-set intervals during periods T2 and T4. Any changes in jumping and maximum kicking velocities during T1 and T3, had trivial effect sizes (0.01-0.15), but small to moderate improvements (effect size = 0.20-0.99) were observed in both groups during T2 and T4. Gains in pre-PHV players were similar for the two inter-set intervals, but gains in post-PHV players were greater (p < 0.05) with an inter-set recovery of 120 s than with a 30 s recovery. We conclude that plyometric jump training improves the physical fitness of adolescents, irrespective of their maturity, but that in older individuals gains are greater with a longer inter-set recovery interval.

#7 How Does the Adjustment of Training Task Difficulty Level Influence Tactical Behavior in Soccer?
Reference: Res Q Exerc Sport. 2019 Jun 3:1-14. doi: 10.1080/02701367.2019.1612511. [Epub ahead of print]
Authors: Machado JC, Barreira D, Teoldo I, Travassos B, Júnior JB, Santos JOLD, Scaglia AJ
Summary: This study aimed to investigate if player tactical skill level and age category influence team performance and player exploratory behavior in tasks with different difficulty levels. In total, 48 youth male soccer players participated in the study (U15, n = 24, mean age = 13.06 ± 1.53 years; U17, n = 24, mean age = 16.89 ± 0.11 years). Player tactical skills were evaluated through the System of Tactical Assessment in Soccer (FUT-SAT), allowing them to be organized into three groups according to tactical efficiency: Higher tactical skill level (Group 01), Intermediate tactical skill level (Group 02), and Lower tactical skill level (Group 03). Next, Group 01 and Group 03 of both categories performed six Small-Sided and Conditioned Games (SSCG) each, namely three High difficulty SSCGs and three Low difficulty SSCGs. Team performance and players' exploratory behavior were analyzed through the Offensive Sequences Characterization System and Lag Sequential Analysis, respectively. We found that team performance and players' exploratory behavior were influenced both by the age and tactical skill level of the players, as well as by task difficulty level. Therefore, in an attempt to improve player performance, practitioners must carefully manipulate key task constraints to adapt training task difficulty levels to player age and tactical skill level.

#8 Influence of Whole-Body Electrostimulation on the Deformability of Density-Separated Red Blood Cells in Soccer Players
Reference: Front Physiol. 2019 May 9;10:548. doi: 10.3389/fphys.2019.00548. eCollection 2019.
Authors: Filipovic A, Bizjak D, Tomschi F, Bloch W, Grau M
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Summary: Red blood cell nitric oxide synthase (RBC-NOS) dependent NO production positively affects RBC deformability which is known to improve oxygen supply to the working tissue. Whole-body electrostimulation (WB-EMS) has been shown to improve maximum strength, sprinting and jumping performance, and to increase deformability in elite soccer players during the season. The aim of the present study was to investigate whether WB-EMS affects RBC turnover which might affect overall deformability of circulating RBC by rejuvenation of the RBC population and if this might be related to improved endurance capacity. Thirty male field soccer players were assigned in either a WB-EMS group (EG, n = 10), a training group (TG, n = 10), or a control group (CG, n = 10). EG performed 3 × 10 squat jumps superimposed with WB-EMS twice per week in concurrent to 2-4 soccer training sessions and one match per week. TG only performed 3 × 10 squat jumps without EMS in addition to their soccer routine and the CG only performed the usual soccer training and match per week. Subjects were tested before (Baseline) and in week 7 (wk-7), with blood sampling before (Pre), 15-30 min after (Post), and 24 h after (24 h post) the training. Endurance capacity was determined before and directly after the training period. The key findings of the investigation indicate an increase in young RBC in the EG group along with improved overall RBC deformability, represented by decreased SS1/2:EImax Ratio. Analysis of the different RBC subfractions revealed improved RBC deformability of old RBC during study period. This improvement was not only observed in the EG but also in TG and CG. Changes in RBC deformability were not associated to altered RBC-NOS/NO signaling pathway. Endurance capacity remained unchanged during study period. In summary, the effect of WB-EMS on RBC physiology seems to be rather low and results are only in part comparable to previous findings. According to the lower training volume of the present study it can be speculated that the soccer specific training load in addition to the WB-EMS was too low to induce changes in RBC physiology.

#9 Comparison of Selected CD45+ Cell Subsets' Response and Cytokine Levels on Exhaustive Effort Among Soccer Players
Reference: J Med Biochem. 2019 May 11;38(3):256-267. doi: 10.2478/jomb-2018-0029. eCollection 2019 Jul.
Authors: Kostrzewa-Nowak D, Buryta R, Nowak R
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Summary: Immunological alterations may led to the reduction in capacity and endurance levels in elite athletes by e.g. increased susceptibility to infections. There is a need to explain the impact of intensive physical effort on the CD4+ memory T cell subsets. Fourteen participants median aged 19 years old (range 17-21 years) were recruited form Pogoń Szczecin S.A., soccer club. They performed progressive efficiency test on mechanical treadmill until exhaustion twice: during preparatory phases to spring and autumn competition rounds. We examined the influence of exhaustive effort on the selected CD45+, especially CD4+ memory T cell subsets and inflammation markers determined before, just after the test and during recovery time. Significant changes in total CD45+ cells and decrease in T lymphocytes percentage after the run was observed. Significant fluctuations in T cells' distribution were related not only to the changes in Th or Tc subsets but also to increase in naïve T cell percentage during recovery. Increase in TNF-α and IL-8 post-exercise, IL-6 and IL-10 plasma levels in recovery was also found. The novel finding of our study is that the run performed on mechanical treadmill caused a significant release of CD4+ T naïve cells into circulation. Post-exercise increase in circulating NK cells is related with fast biological response to maximal effort. However, at the same time an alternative mechanism enhancing inflammation is involved.

#10 Chronic traumatic encephalopathy is a common co-morbidity, but less frequent primary dementia in former soccer and rugby players
Reference: Acta Neuropathol. 2019 Jun 1. doi: 10.1007/s00401-019-02030-y. [Epub ahead of print]
Authors: Lee EB, Kinch K, Johnson VE, Trojanowski JQ, Smith DH, Stewart W
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Summary: Chronic traumatic encephalopathy (CTE) is reported at high prevalence in selected autopsy case series of former contact sports athletes. Nevertheless, the contribution of CTE pathology to clinical presentation and its interaction with co-morbid neurodegenerative pathologies remain unclear. To address these issues, we performed comprehensive neuropathology assessments on the brains of former athletes with dementia and considered these findings together with detailed clinical histories to derive an integrated clinicopathological diagnosis for each case. Consecutive, autopsy-acquired brains from former soccer and rugby players with dementia were assessed for neurodegenerative pathologies using established and preliminary consensus protocols. Thereafter, next of kin interviews were conducted to obtain detailed accounts of the patient's clinical presentation and course of disease to inform a final, integrated clinicopathological diagnosis. Neuropathologic change consistent with CTE (CTE-NC) was confirmed in five of seven former soccer and three of four former rugby players' brains, invariably in combination with mixed, often multiple neurodegenerative pathologies. However, in just three cases was the integrated dementia diagnosis consistent with CTE, the remainder having alternate diagnoses, with the most frequent integrated diagnosis Alzheimer's disease (AD) (four cases; one as mixed AD and vascular dementia). This consecutive autopsy series identifies neuropathologic change consistent with preliminary diagnostic criteria for CTE (CTE-NC) in a high proportion of former soccer and rugby players dying with dementia. However, in the majority, CTE-NC appears as a co-morbidity rather than the primary, dementia causing pathology. As such, we suggest that while CTE-NC might be common in former athletes with dementia, in many cases its clinical significance remains uncertain.

#11 Enhanced sprint performance analysis in soccer: New insights from a GPS-based tracking system
Reference: PLoS One. 2019 May 31;14(5):e0217782. doi: 10.1371/journal.pone.0217782. eCollection 2019.
Authors: Reinhardt L, Schwesig R, Lauenroth A, Schulze S, Kurz E
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Summary: The aim of this investigation was to establish the validity of a GPS-based tracking system (Polar Team Pro System, PTPS) for estimating sprint performance and to evaluate additional diagnostic indices derived from the temporal course of the movement velocity. Thirty-four male soccer players (20 ± 4 years) performed a 20 m sprint test measured by timing gates (TG), and while wearing the PTPS. To evaluate the relevance of additional velocity-based parameters to discriminate between faster and slower athletes, the median-split method was applied to the 20-m times. Practical relevance was estimated using standardized mean differences (d) between the subgroups. Differences between the criterion reference (TG) and PTPS for the 10 and 20 m splits did not vary from zero (dt10: -0.01 ± 0.07 s, P = 0.7, d < -0.1; dt20: -0.01 ± 0.08 s, P = 0.4, d < -0.2). Although subgroups revealed large differences in their sprint times (d = -2.5), the average accelerations between 5 and 20 km/h as well as 20 and 25 km/h showed merely small effects (d < 0.5). Consequently, analyses of velocity curves derived from PTPS may help to clarify the occurrence of performance in outdoor sports. Thus, training consequences can be drawn which contribute to the differentiation and individualization of sprint training.

#12 Epidemiology of injuries in professional football: a systematic review and meta-analysis
Reference: Br J Sports Med. 2019 Jun 6. pii: bjsports-2018-099577. doi: 10.1136/bjsports-2018-099577. [Epub ahead of print]
Authors: López-Valenciano A, Ruiz-Pérez I, Garcia-Gómez A, Vera-Garcia FJ, De Ste Croix M, Myer GD, Ayala F
Summary: We performed a systematic review and meta-analysis of epidemiological data of injuries in professional male football. Forty-four studies have reported the incidence of injuries in football. Two reviewers independently extracted data and assessed trial quality using the Strengthening the Reporting of Observational Studies in Epidemiology statement and Newcastle Ottawa Scale. Studies were combined in a pooled analysis using a Poisson random effects regression model. The overall incidence of injuries in professional male football players was 8.1 injuries/1000 hours of exposure. Match injury incidence (36 injuries/1000 hours of exposure) was almost 10 times higher than training injury incidence rate (3.7 injuries/1000 hours of exposure). Lower extremity injuries had the highest incidence rates (6.8 injuries/1000 hours of exposure). The most common types of injuries were muscle/tendon (4.6 injuries/1000 hours of exposure), which were frequently associated with traumatic incidents. Minor injuries (1-3 days of time loss) were the most common. The incidence rate of injuries in the top 5 European professional leagues was not different to that of the professional leagues in other countries (6.8 vs 7.6 injuries/1000 hours of exposure, respectively). Professional male football players have a substantial risk of sustaining injuries, especially during matches.

#13 P