Latest research in football - week 17 - 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 In-season internal and external training load quantification of an elite European soccer team
Reference: PLoS One. 2019 Apr 22;14(4):e0209393. doi: 10.1371/journal.pone.0209393. eCollection 2019.
Authors: Oliveira R, Brito JP, Martins A, Mendes B, Marinho DA, Ferraz R, Marques MC
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Summary: Elite soccer teams that participate in European competitions need to have players in the best physical and psychological status possible to play matches. As a consequence of congestive schedule, controlling the training load (TL) and thus the level of effort and fatigue of players to reach higher performances during the matches is therefore critical. Therefore, the aim of the current study was to provide the first report of seasonal internal and external training load that included Hooper Index (HI) scores in elite soccer players during an in-season period. Nineteen elite soccer players were sampled, using global position system to collect total distance, high-speed distance (HSD) and average speed (AvS). It was also collected session rating of perceived exertion (s-RPE) and HI scores during the daily training sessions throughout the 2015-2016 in-season period. Data were analysed across ten mesocycles (M: 1 to 10) and collected according to the number of days prior to a one-match week. Total daily distance covered was higher at the start (M1 and M3) compared to the final mesocycle (M10) of the season. M1 (5589m) reached a greater distance than M5 (4473m) (ES = 9.33 [12.70, 5.95]) and M10 (4545m) (ES = 9.84 [13.39, 6.29]). M3 (5691m) reached a greater distance than M5 (ES = 9.07 [12.36, 5.78]), M7 (ES = 6.13 [8.48, 3.79]) and M10 (ES = 9.37 [12.76, 5.98]). High-speed running distance was greater in M1 (227m), than M5 (92m) (ES = 27.95 [37.68, 18.22]) and M10 (138m) (ES = 8.46 [11.55, 5.37]). Interestingly, the s-RPE response was higher in M1 (331au) in comparison to the last mesocycle (M10, 239au). HI showed minor variations across mesocycles and in days prior to the match. Every day prior to a match, all internal and external TL variables expressed significant lower values to other days prior to a match (p<0.01). In general, there were no differences between player positions. Conclusions: Our results reveal that despite the existence of some significant differences between mesocycles, there were minor changes across the in-season period for the internal and external TL variables used. Furthermore, it was observed that MD-1 presented a reduction of external TL (regardless of mesocycle) while internal TL variables did not have the same record during in-season match-day-minus.

#2 Comparison of Physical Fitness and Anthropometrical Profiles Among Brazilian Female Soccer National Teams From U15 to Senior Categories
Reference: J Strength Cond Res. 2019 Apr 11. doi: 10.1519/JSC.0000000000003140. [Epub ahead of print]
Authors: Ramos GP, Nakamura FY, Penna EM, Mendes TT, Mahseredjian F, Lima AM, Garcia ES, Prado LS, Coimbra CC
Summary: This study aimed to compare anthropometric and physical fitness of Brazilian female national team soccer players from the U15 to senior categories, and to compare the physical performance between selected and nonselected players. Subjects included 231 athletes (U15, n = 46, U17, n = 49, U20, n = 98, and Senior, n = 38). Body mass, height, sum of skinfolds, squat jump (SJ), countermovement jump (CMJ), 20-m linear sprint, and Yo-Yo IR1 were assessed. The U15 players were shorter than all other groups (p < 0.01) and lighter than U20 players (p < 0.01). Regarding physical tests, Senior athletes presented higher SJ compared with U20, and both showed higher CMJ and SJ compared with the U15 and U17 (p < 0.05). Senior athletes were also faster than players of all other categories in 20-m sprint (p < 0.01) and covered the greatest distance in the Yo-Yo IR1 (p < 0.05). U20 were better in the Yo-Yo IR1 than the younger groups (p < 0.05). When comparing selected and nonselected players, no differences were identified in anthropometric measures (p > 0.05). However, selected players from U17, U20, and Senior teams showed better performance in Yo-Yo IR1 than nonselected ones (p < 0.05). Finally, selected senior athletes also presented higher CMJ and SJ than nonselected players (p < 0.05). These results suggest that, although there is a tendency for maintenance in anthropometric measures from the age of 15 years, there are substantial improvements in speed, lower-body power, and aerobic capacity from U20 age group. In addition, it seems that intermittent aerobic fitness contributes to the selection of players to international tournaments in national teams.

#3 Effects of Interlimb Asymmetries on Acceleration and Change of Direction Speed: A Between-Sport Comparison of Professional Soccer and Cricket Athletes
Reference: J Strength Cond Res. 2019 Apr 16. doi: 10.1519/JSC.0000000000003135. [Epub ahead of print]
Authors: Bishop C, Read P, Brazier J, Jarvis P, Chavda S, Bromley T, Turner A
Summary: The first aim of this study was to quantify and compare asymmetries among professional soccer and cricket athletes. The second aim was to examine the association between asymmetries and performance within both groups. Professional soccer (n = 18) and cricket (n = 23) athletes performed single-leg countermovement jumps, single-leg drop jumps (SLDJs), a 10-m sprint, and 505 change of direction speed (CODS) tests. Interlimb asymmetries were calculated as a standard percentage difference, Mann-Whitney U tests conducted to establish systematic bias between groups, and Spearman's r correlations used to establish the relationship between asymmetry scores and speed and CODS performance. Soccer athletes sprinted faster, jumped higher, and had a greater reactive strength index (RSI) score than cricket athletes (p < 0.05). However, cricketers showed reduced ground contact times compared with footballers during the SLDJ (p < 0.05). The cricket group showed significantly greater jump height (asymmetry = 11.49 vs. 6.51%; p = 0.015) and RSI (asymmetry = 10.37 vs. 5.95%; p = 0.014) asymmetries compared with soccer players. These metrics were also associated with slower 505 times in the cricket group only (r = 0.56 -0.74; p < 0.01). These results show that between-limb asymmetries exhibit no association with speed and CODS in elite soccer players but are associated with reduced CODS in elite cricketers. Thus, the reduction of interlimb asymmetries may be of greater consideration when working with cricket vs. soccer athletes.

#4 Dose-Response Relationship Between Internal Training Load and Changes in Performance During the Preseason in Youth Soccer Players
Reference: J Strength Cond Res. 2019 Apr 16. doi: 10.1519/JSC.0000000000003126. [Epub ahead of print]
Authors: Figueiredo DH, Figueiredo DH, Moreira A, Gonçalves HR, Dourado AC
Summary: The aim of this study was to describe training intensity distribution based on the session rating of perceived exertion (sRPE) and heart rate (HR) methods and examine the dose-response relation between internal training load (ITL) and change in performance of 16 youth soccer players (mean ± SD age: 18.75 ± 0.68 years, height: 175.3 ± 5.5 cm, body mass: 68.7 ± 6.5 kg, and body fat: 10.7 ± 1.2%) belonging to a Brazilian first division team during a 3-week preseason. The sRPE and HR data were registered daily to calculate the ITL and the training intensity distribution, in 3 intensity zones (low, moderate, and high). The Yo-yo Intermittent Recovery Level 1 (Yo-yo IR1) was evaluated before and after experimental period. The total time spent in the low-intensity zone (HR method) was greater (p < 0.01) compared with the moderate- and high-intensity zones. No difference was observed between training intensity zones determined by the sRPE method (p > 0.05). Negative correlations were observed between weekly mean sRPE-TL (r = -0.69), Edward's-TL (r = -0.50), and change in Yo-yo IR1. Linear regression indicated that weekly mean sRPE-TL (F1;14 = 13.3; p < 0.01) and Edward's-TL (F1;14 = 4.8; p < 0.05) predicted 48.7 and 25.5% of the variance in performance change, respectively. Stepwise linear regression revealed that these 2-predictor variables (F2;13 = 18.9; p < 0.001) explained 74.5% of the variance in performance change. The results suggest that the sRPE and HR methods cannot be used interchangeably to determine training intensity distribution. Moreover, sRPE-TL seems to be more effective than the HR-based TL method to predict changes in performance in youth soccer players.

#5 Activity Profiles of Top-Class Players and Referees and Accuracy in Foul Decision-Making During Korean National League Soccer Games
Reference: J Strength Cond Res. 2019 Apr 16. doi: 10.1519/JSC.0000000000003083. [Epub ahead of print]
Authors: Joo CH, Jee H
Summary: The aims of this study were to compare the activity profiles between the top-class referees and players and elucidate the factors related to foul decision-making. Three hundred thirty-five elite-level players and referees were analyzed for distance covered during 20 matches of nationally held 2016 Korean league competitions. Distance covered by the players and referees was analyzed for the activity zones (slow walking, walking, jogging, running, high-intensity running, and sprinting) and 15-minute match periods. Mean distance between foul play and referee locations, foul plays, and 15-minute match periods were compared with the foul decision errors. Foul play and decision error rates (%) were also analyzed per segmented pitch zone. Although the total distance covered during a match and distances covered by jogging, running, and sprinting were significantly different between the players and referees, differences were within 1%. Significant differences in the distance covered before and after halftime were observed. The greatest distance between the foul play and referee locations, number of foul plays, and number of foul decision errors were observed at the 75-minute match period. Finally, the greater number of foul plays was observed in the neutral and attacking zones, and the foul decision errors were observed in the right defensive and left attacking zones 1. In conclusion, although the activity profiles may be different, referees should maintain certain level of physical fitness to match that of the players. To reduce the number of foul decision errors, factors such as match time, foul occurring location, and distance between foul play and referee locations should be considered.

#6 Are specific players more likely to be involved in high-magnitude head impacts in youth football?
Reference: J Neurosurg Pediatr. 2019 Apr 26:1-7. doi: 10.3171/2019.2.PEDS18176. [Epub ahead of print]
Authors: Gellner RA, Campolettano ET, Smith EP, Rowson S
Summary: Youth football attracts approximately 3.5 million participants every year, but concern has recently arisen about the long-term effects of experiencing repetitive head accelerations from a young age due to participation in football. The objective of this study was to quantify total involvement in high-magnitude impacts among individual players in youth football practices. The authors explored the relationship between the total number of high-magnitude accelerations in which players were involved (experienced either by themselves or by other players) during practices and the number of high-magnitude accelerations players experienced. local cohort of 94 youth football players (mean age 11.9 ± 1.5, mean body mass 50.3 ± 16.4 kg) from 4 different teams were recruited and outfitted with helmet-mounted accelerometer arrays. The teams were followed for one season each for a total of 128 sessions (practices, games, and scrimmages). All players involved in high-magnitude (greater than 40g) head accelerations were subsequently identified through analysis of practice film. Players who experienced more high-magnitude accelerations were more likely to be involved in impacts associated with high-magnitude accelerations in other players. A small subset of 6 players (6%) were collectively involved in 230 (53%) high-magnitude impacts during practice, were involved in but did not experience a high-magnitude acceleration 78 times (21% of the 370 one-sided high-magnitude impacts), and experienced 152 (30%) of the 502 high-magnitude accelerations measured. Quarterbacks/running backs/linebackers were involved in the greatest number of high-magnitude impacts in practice and experienced the greatest number of high-magnitude accelerations. Which team a player was on was an important factor, as one team showed much greater head impact exposure than all others. This study showed that targeting the most impact-prone players for individualized interventions could reduce high-magnitude acceleration exposure for entire teams. These data will help to further quantify elevated head acceleration exposure and enable data-driven interventions that modify exposure for individual players and entire teams.

#7 Bilateral Simultaneous Tibial Tubercle Avulsion in an Adolescent Football Player with Previous Bilateral Osgood-Schlatter Disease
Reference: Case Rep Orthop. 2019 Mar 24;2019:8535370. doi: 10.1155/2019/8535370. eCollection 2019.
Authors: Dalla Rosa Nogales J, Nogales Zafra JJ
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Summary: Tibial tubercle avulsion fractures are a very uncommon injury, accounting between 0.4 and 2.7% of all epiphyseal injuries. Bilateral lesions are extremely rare with only 20 cases described in the literature. They occur more frequently in male adolescents and during sport activities that require jumping and sprinting, such as football or basketball. We report the case of a 13-year-old boy who sustained simultaneous bilateral tibial avulsion fractures on the background of a previous conservatively managed bilateral Osgood-Schlatter disease.

#8 Working Memory Training in Professional Football Players: A Small-Scale Descriptive Feasibility Study-The Importance of Personality, Psychological Well-Being, and Motivational Factors
Reference: Sports (Basel). 2019 Apr 18;7(4). pii: E89. doi: 10.3390/sports7040089.
Authors: In de Braek D, Deckers K, Kleinhesselink T, Banning L, Ponds R
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Summary: Working memory training (WMT) programs can improve working memory (WM). In football players, this could lead to improved performance on the pitch. Eighteen professional football players of Maatschappelijke Voetbal Vereniging Maastricht (MVV) participated and followed an online, computerized WMT program. Neuropsychological performance, psychological wellbeing, self-efficacy, and football skills (Loughborough Soccer Passing Test; LSPT) were assessed at three time points, before and after WMT and at three-month follow-up. Descriptive data are reported. Baseline characteristics were roughly similar for both groups. Participants performed better on the trained WM tasks, but performance for other neuropsychological test measures or the LSPT did not change. Low compliance rates were observed, showing differences in personality and well-being between compliers and non-compliers. WMT is not a feasible and effective strategy to improve non-trained cognitive measures and football performance. However, this study indicates that it is important to take individual characteristics into account.

#9 Are Hip Physical Examination Findings Predictive of Future Lower Body Injury Rates in Elite Adolescent Female Soccer Athletes at Minimum 5-Year Follow-Up?
Reference: J Sport Rehabil. 2019 Apr 29:1-26. doi: 10.1123/jsr.2018-0350. [Epub ahead of print]
Authors: Cheng AL, Merlo JA, Hunt D, Yemm T, Brophy RH, Prather H
Summary: While elite adolescent female soccer athletes have unique injury risk factors and management challenges, limited epidemiological data exist for this population. Describe lower body injury patterns and determine whether a screening hip physical examination is predictive of future injuries in elite adolescent female soccer athletes. One hundred seventy-seven female soccer athletes ages 10-18 years old (mean 14.6±1.8 years) completed a demographic questionnaire and screening hip physical examination which included range of motion and provocative tests. At least five years after baseline screening, athletes completed an electronic follow-up injury survey. Injury was defined as pain that interfered with sporting activity. In addition to descriptive analyses of athletes' injury profiles, associations between players' baseline demographics and subsequent injury profiles were evaluated using chi-square tests, and potential predictors of injury based on players' baseline hip examinations were evaluated using multivariable logistic regression. Ninety-four of 177 athletes (53%) were contacted for follow-up, and 88/94 (93.6%) completed the survey. With mean follow-up of 91.9±9.3 months (range 66-108 months), 42/88 (47.7%) reported sustaining a new lower body injury. The low back was the most commonly injury region (16/42, 38.1%). Almost half of all injured athletes (20/42, 47.6%) sustained overuse injuries, and 16/42 (38.1%) had an incomplete recovery. Higher body mass index and reaching menarche were associated with sustaining an injury (p=0.03 and 0.04, respectively). Athletes' baseline hip examinations were not predictive of their subsequent rate of lower body, lumbopelvic, overuse, or incomplete recovery injury (all p>0.05). Lower body injuries were common in elite adolescent female soccer athletes, with over one third of injured athletes reporting permanent negative impact of the injury on their playing ability. Baseline hip physical examinations were not associated with future injury rate.

#10 Respiratory Frequency as a Marker of Physical Effort During High-Intensity Interval Training in Soccer Players
Reference:  Int J Sports Physiol Perform. 2019 Apr 29:1-24. doi: 10.1123/ijspp.2019-0028. [Epub ahead of print]
Authors: Nicolò A, Montini M, Girardi M, Felici F, Bazzucchi I, Sacchetti M
Summary: Variables currently used in soccer training monitoring fail to represent the physiological demand of the player during movements like accelerations, decelerations and directional changes performed at high intensity. We tested the hypothesis that respiratory frequency (fR) is a marker of physical effort during soccer-related high-intensity exercise. Twelve male soccer players performed a preliminary intermittent incremental test and two shuttle-run high-intensity interval training (HIIT) protocols, in separate visits. The two HIIT protocols consisted of 12 repetitions over 9 min and differed in the work-recovery ratio (15:30s vs. 30:15s). Work rate was self-paced by participants to achieve the longest possible total distance in each HIIT protocol. Work-phase average metabolic power was higher (P < 0.001) in the 15:30s (31.7 ± 3.0 W·kg-1) compared to the 30:15s (22.8 ± 2.0 W·kg-1). Unlike heart rate and V̇O2, fR showed a fast response to the work-recovery alternation during both HIIT protocols, resembling changes in metabolic power even at supramaximal intensities. Large correlations (P < 0.001) were observed between fR and rating of perceived exertion during both 15:30s (r = 0.87) and 30:15s (r = 0.85). Our findings suggest that fR is a good marker of physical effort during shuttle-run HIIT in soccer players. These findings have implications for monitoring training in soccer and other team sports.

#11 Case Study: Muscle Atrophy, Hypertrophy and Energy Expenditure of a Premier League Soccer Player During Rehabilitation From ACL Injury
Reference: Int J Sport Nutr Exerc Metab. 2019 Apr 29:1-17. doi: 10.1123/ijsnem.2018-0391. [Epub ahead of print]
Authors: Anderson L, Close GL, Konopinksi M, Rydings D, Milsom J, Hambly C, Speakman JR, Drust B, Morton JP
Summary: Maintaining muscle mass and function during rehabilitation from anterior cruciate ligament (ACL) injury is complicated by the challenge of accurately prescribing daily energy intakes aligned to energy expenditure. Accordingly, we present a 38-week case study characterizing whole body and regional rates of muscle atrophy and hypertrophy (as inferred by assessments of fat free mass from DXA) in a professional male soccer player from the English Premier League. Additionally, in week 6 we also quantified energy intake (via the remote food photographic method) and energy expenditure using the doubly labeled water method. Mean daily energy intake (CHO: 1.9-3.2, Protein: 1.7-3.3 and Fat: 1.4-2.7 and energy expenditure was 2765 ± 474 and 3178 kcal.d-1 respectively. In accordance with an apparent energy deficit, total body mass decreased by 1.9 kg during week 1-6 where FFM loss in the injured and non-injured limb was 0.9 and 0.6 kg, respectively, yet, trunk FFM increased by 0.7 kg. In weeks 7-28, the athlete was advised to increased daily CHO intake (4-6 to facilitate an increased daily energy intake. Throughout this period, total body mass increased by 3.6 kg (attributable to a 2.9 and 0.7 kg increase in fat-free and fat mass, respectively). Our data suggest it may be advantageous to avoid excessive reductions in energy intake during the initial 6-8 weeks post-ACL surgery so as to limit muscle atrophy.

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