Latest research in football - week 3 - 2021

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 Global Positioning System Analysis of Physical Demands in Small and Large-Sided Games with Floaters and Official Matches in the Process of Return to Play in High Level Soccer Players

Reference: Sensors (Basel). 2020 Nov 18;20(22):6605. doi: 10.3390/s20226605. 

Authors: Demetrio Lozano, Miguel Lampre, Adrián Díez, Oliver Gonzalo-Skok , Diego Jaén-Carrillo, Daniel Castillo, José Luis Arjol 

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Summary: The aim of this study was twofold: (i) to analyze the physical demands in the return to play (RTP) process of high-level soccer players in the role of floater in different soccer sided games (SGs) formats (i.e., 4vs4 + 2 and 8vs8 + 1); and (ii) to analyze the differences in physical demands encountered by regular and floater players among the SGs formats and official matches by means of global positioning system technology (GPS APEX pod, North Ireland) was used. Twenty-six highly trained, male soccer players (U16 years) participated in this investigation. Players were classified into two groups: 23 regular and 3 floater players, a total of eight SGs were analyzed, which involved the recording of 80 observations of regular and floater players. Match-play players showed most likely-probable differences in distance covered at high-intensity per minute (D > 14.4/min), at high-speed running per minute (D > 21/min), and peak velocity (Vpeak) in comparison to floaters in the 8vs8 + 1 LSG (large-side-games), and presented most likely differences in accelerations >2/min in comparison to match-play players. Therefore, the use of floaters during the last phase of the RTP (return to play) seems to be a useful strategy for progressive reintroduction into specific training (1) floater in the 4vs4 + 2 SSG; (2) floater in the 8vs8 + 1 LSG; (3) regular player in the 4vs4 + 2 SSG; and (4) regular player in the 8vs8 + 1 LSG before starting full trainings and returning to competition. 



#2 The Training of Short Distance Sprint Performance in Football Code Athletes: A Systematic Review and Meta-Analysis 

Reference: Sports Med. 2020 Nov 27. doi: 10.1007/s40279-020-01372-y. Online ahead of print. 

Authors: Ben Nicholson, Alex Dinsdale, Ben Jones, Kevin Till

Summary: Short-sprint (≤ 20 m) performance is an important quality for success in the football codes. Therefore, developing an evidence base for understanding training methods to enhance short-sprint performance is key for practitioners. However, current systematic reviews are limited by (1) a lack of focus on football code athletes, (2) a lack of consideration of all training modalities and (3) a failure to account for the normal training practices undertaken by intervention groups within their analysis. Therefore, this review aimed to (1) conduct a systematic review of the scientific literature evaluating training interventions upon short-sprint performance within football code athletes, (2) undertake a meta-analysis to assess the magnitude of change of sport-sprint performance following training interventions and (3) identify how moderator variables affect the training response. A systematic search of electronic databases was conducted. A random-effects meta-analysis was performed to establish standardised mean difference with 95% confidence intervals. This identified the magnitude and direction of the individual training effects of intervention subgroups (primary, secondary, combined-specific, tertiary and combined training methods) on short-sprint performance while considering moderator variables (i.e., football code, sex, age, playing standard, phase of season). 121 studies met the inclusion criteria, totalling 3419 athletes. Significant improvements (small-large) were found between pre- and post-training in short-sprint performance for the combined, secondary, tertiary and combined-specific training methods. No significant effect was found for primary or sport only training. No individual mode was found to be the most effective. Between-subgroup analysis identified that football code, age, playing standard and phase of season all moderated the overall magnitude of training effects. This review provides the largest systematic review and meta-analysis of short-sprint performance development methods and the only one to assess football code athletes exclusively. Practitioners can apply combined, secondary and tertiary training methods to improve short-sprint performance within football code athletes. The application of sport only and primary methods does not appear to improve short-sprint performance. Regardless of the population characteristics, short-sprint performance can be enhanced by increasing either or both the magnitude and the orientation of force an athlete can generate in the sprinting action. 



#3 Youth Football Players' Psychological Well-Being: The Key Role of Relationships

Reference: Front Psychol. 2020 Nov 10;11:567776. doi: 10.3389/fpsyg.2020.567776. eCollection 2020. 

Authors: Eleonora Reverberi, Chiara D'Angelo, Martin A Littlewood, Caterina Francesca Gozzoli  1 

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Summary: Well-being in youth sport is a growing topic in literature. Practicing sports at a youth level is recognized as an important opportunity for growth and development but also an experience that conversely can prove to be tiring and cause discomfort. Sometimes expectations and pressures make it a risky experience. This is emphasized even more when looking at very popular and spectacular sports, such as football in some European Countries; practicing football often solicits the hope of becoming champions one day and thus being able living thanks to the beloved sport. How do young Italian football practitioners feel? What role do relationships with significant others belonging to the world of sport and extra-sport play on the well-being of young athletes? On which specific aspects of psychological well-being (PWB) are these relationships based? Are there any differences between elite and amateurs levels? These are the questions upon which this paper focuses, considering a sample of young Italian football practitioners. Analysis reveals a strong and positive influence of some dimensions of the relationships with significant others on PWB, specifically team effort, coach closeness, and parental learning climate. Moreover, elite players perceive significantly better relationships than sub-elite and amateurs and have significantly higher levels of PWB. Those results provide a first evidence for the importance of good relationships within and outside sport for an effective development of youth football players since they positively influence players' PWB, which is higher in elite players. It emerges the necessity to further investigate different aspects of PWB and to deepen the knowledge about the meaning of relationship in developmental athletes according to a psychosocial approach. 



#4 Performance Effects with Injury Prevention Exercise Programmes in Male Youth Football Players: A Randomised Trial Comparing Two Interventions 

Reference: Sports Med Open. 2020 Nov 23;6(1):56. doi: 10.1186/s40798-020-00282-7. 

Authors: Hanna Lindblom, Markus Waldén, Martin Hägglund

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Summary: Increased performance from injury prevention exercise programmes (IPEPs) may affect injury risks positively and support the implementation of IPEPs. The primary aim was to study the performance effects of injury prevention exercises from two different IPEPs, the Knee Control IPEP and the further developed Knee Control+ IPEP, in youth male football players, and the secondary aim was to compare potential differences in performance effects between the IPEPs. Four male youth football teams were tested for agility, hop and sprint performance at the start of the second half of the competitive season and after the end of the 8-week season. Per randomisation, two teams used Knee Control and two teams Knee Control+. In total, 47 players executed a median of 13 IPEP sessions (range 11-21 sessions). No improvements in performance were seen in the group as a whole. The intervention groups showed small declines in sprint and agility performance. There was a significant between-group difference in change for the 505 agility test, with improved performance in the Knee Control and worse performance in the Knee Control+ group, ΔKC vs KC+ = - 0.012 (95% CI - 0.19 to -0.04), d = 0.98. No clinically meaningful performance effects were seen from the Knee Control or Knee Control+ IPEP in youth male athletes and no meaningful differences were seen between Knee Control and Knee Control+ regarding effects on performance tests. 



#5 Assessment of the Dietary Intake of High-Rank Professional Male Football Players during a Preseason Training Week 

Reference: Int J Environ Res Public Health. 2020 Nov 18;17(22):8567. doi: 10.3390/ijerph17228567. 

Authors: Anna Książek, Aleksandra Zagrodna, Małgorzata Słowińska-Lisowska 

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Summary: A well-balanced diet is one of the main factors that may play a supportive role in enhancing acute training stimuli in optimal training adaptation. The aim of the present study was to examine the energy and macro- and micronutrient intake including and excluding supplements among top-level Polish football players during one week of the general preparatory period. In addition, the study looked at whether athletes consume carbohydrates in recommended amounts, depending on the completed training sessions. A total of 26 professional football players were included in the study. The preseason dietary intake was assessed using a 7-day estimated food record. The energy value of the diet and the amounts of the dietary ingredients were assessed using the software Dieta 6.0. The average consumption of energy, vitamin B2, vitamin C, vitamin E, folate, and calcium was lower than recommendations, and average intake of sodium and potassium was higher than the norm in the diets of the athletes. The results of this study do not confirm the justification for adding protein preparations to diets of the studied players. Furthermore, football players dietary carbohydrate intake was relatively low in comparison to requirements based on training loads. Based on our results we conclude that further work is necessary to reinforce education about nutritional habits and adjust nutritional strategies to individual needs to enhance athletic performance. 



#6 Interpretation of elevated high-sensitivity cardiac troponin I in elite soccer players previously infected by severe acute respiratory syndrome coronavirus 2 

Reference: Int J Cardiol. 2020 Nov 23;S0167-5273(20)34162-0. doi: 10.1016/j.ijcard.2020.11.039. Online ahead of print. 

Authors: Giuseppe Mascia, Fabio Pescetelli, Amedeo Baldari, Piero Gatto, Sara Seitun, Paolo Sartori, Maurizio Pieroni, Leonardo Calò, Roberta Della Bona, Italo Porto

Summary: The aim was to clarify the meaning of elevated cardiac troponin in elite football athletes previously infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and screened for cardiovascular involvement in the wake of competitive sport resumption. We designed a retrospective cohort study with the collaboration of two Italian Serie A teams. Football players from both rosters (58 athletes) were systematically analysed. For every SARS-CoV-2 positive athlete, the Italian Football Federation protocol requested full blood tests including high-sensitivity cardiac troponin I (hscTnI), along with a complete cardiovascular examination. We extended the analysis to SARS-CoV-2 negative athletes. A total of 13/58 players (22.4%) suffered from SARS-CoV-2infection: all had a negative cardiovascular examination and 2/13 (15%) showed increased hs-cTnI values (120,8 pg/ml and 72,6 pg/ml, respectively; upper reference level 39,2 pg/ml), which did not track with inflammatory biomarkers. Regarding the 45/58 (77,6%) non infected athletes, a slight increase in hs-cTnI was observed in 2 (4.5%) subjects (values: 61 pg/ml and 75 pg/ml respectively). All hs-cTnI positive athletes (4/58, 7%) underwent cardiac magnetic resonance (CMR), that excluded any cardiac injury. In our retrospective study, SARS-CoV-2 infection in elite football athletes was not associated to clinical or biomarkers abnormalities. Increased hs-cTnI was rare and not significantly associated with previous SARS-COV2 infection nor with pathological findings at CMR, albeit elevated hs-cTnI was numerically more prevalent in the infected group. 



#7 Using Behavioral Skills Training With Video Feedback to Prevent Risk of Injury in Youth Female Soccer Athletes 

Reference: Behav Anal Pract. 2020 Aug 17;13(4):811-819. doi: 10.1007/s40617-020-00473-4. eCollection 2020 Dec. 

Authors: Marrissa Harris, Laura Baylot Casey, James N Meindl, Douglas Powell, William C Hunter, Diana Delgado 

Summary: Female athletes are at a greater risk for anterior cruciate ligament (ACL) injuries than males. Current training programs for ACL injury reduction focus on muscle strengthening, appropriate movement patterns, and balance training. However, there is limited research on effective strategies to teach youth female soccer athletes how to properly perform desired movements associated with a decreased risk of ACL injuries. Behavioral skills training (BST) programs have been shown to be effective in teaching a wide variety of skills, but research on applications to sports is limited. This study evaluated a BST package for teaching a stepwise agility program to 3 youth female soccer athletes that consisted of verbal instructions, modeling, rehearsal, and feedback, which included video replay. Results showed a significant improvement in the number of steps the participants performed correctly relative to baseline, as well as maintenance of skills at follow-up. Implications for coaches and athletes, as well as limitations and directions for future research, are discussed. 



#8 Entropy Analysis of Soccer Dynamics 

Reference: Entropy (Basel). 2019 Feb 16;21(2):187. doi: 10.3390/e21020187. 

Authors: António M Lopes, J A Tenreiro Machado

Summary: This paper adopts the information and fractional calculus tools for studying the dynamics of a national soccer league. A soccer league season is treated as a complex system (CS) with a state observable at discrete time instants, that is, at the time of rounds. The CS state, consisting of the goals scored by the teams, is processed by means of different tools, namely entropy, mutual information and Jensen-Shannon divergence. The CS behavior is visualized in 3-D maps generated by multidimensional scaling. The points on the maps represent rounds and their relative positioning allows for a direct interpretation of the results. 



#9 Effects of Plyometric Jump Training in Female Soccer Player's Physical Fitness: A Systematic Review with Meta-Analysis 

Reference: Int J Environ Res Public Health. 2020 Nov 30;17(23):E8911. doi: 10.3390/ijerph17238911. 

Authors: Mario Sánchez, Javier Sanchez-Sanchez, Fabio Y Nakamura, Filipe M Clemente, Blanca Romero-Moraleda, Rodrigo Ramirez-Campillo

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Summary: We aimed to assess the effects of plyometric jump training (PJT) on female soccer player's physical fitness. To this aim, a systematic review with meta-analysis (SRMA) was conducted. The electronic databases PubMed, MEDLINE, Web of Science, and SCOPUS were used. To qualify for inclusion, peer-reviewed studies must have included (i) a PJT programme of ≥2 weeks, (ii) healthy athletes, (iii) a control group, and (iv) physical fitness outcomes (e.g., jump; sprint). Studies were excluded if (i) they incorporated injuried female soccer players, (ii) did not involve PJT or an active control group, (iv) lack of baseline and/or follow-up data. Data was meta-analyzed using the inverse variance random-effects model. Ten moderate-to-high quality studies were included in the analyses, comprising 13 training groups (n = 140) and 10 control groups (n = 110). Small to large (ES = 0.60-2.24; p = 0.040 to <0.001) effects were noted for countermovement jump, drop jump, kicking performance, linear sprint, change of direction speed, and endurance. The moderator analyses (i.e., PJT duration, age groups, competitive level, and soccer experience) revealed no significant differences between groups. In conclusion, PJT may improve the physical fitness of female soccer players. Such improvements might be expected after PJT interventions with six or more weeks of duration, and in players with different chronological ages, competitive levels and soccer experience. 



#10 The Adaptive Behavior of a Soccer Team: An Entropy-Based Analysis 

Reference: Entropy (Basel). 2018 Oct 2;20(10):758. doi: 10.3390/e20100758. 

Authors: Yair Neuman , Navot Israeli, Dan Vilenchik, Yochai Cohen

Summary: To optimize its performance, a competitive team, such as a soccer team, must maintain a delicate balance between organization and disorganization. On the one hand, the team should maintain organized patterns of behavior to maximize the cooperation between its members. On the other hand, the team's behavior should be disordered enough to mislead its opponent and to maintain enough degrees of freedom. In this paper, we have analyzed this dynamic in the context of soccer games and examined whether it is correlated with the team's performance. We measured the organization associated with the behavior of a soccer team through the Tsallis entropy of ball passes between the players. Analyzing data taken from the English Premier League (2015/2016), we show that the team's position at the end of the season is correlated with the team's entropy as measured with a super-additive entropy index. Moreover, the entropy score of a team significantly contributes to the prediction of the team's position at the end of the season beyond the prediction gained by the team's position at the end of the previous season. 



#11 Effect of Training and Match Loads on Hamstring Passive Stiffness in Professional Soccer Players 

Reference: J Musculoskelet Neuronal Interact. 2020 Dec 1;20(4):488-497. 

Authors: Danguole Satkunskiene, Tiago M da Silva, Sigitas Kamandulis, Nuno M C Leite, Aurelijus Domeika, Mantas Mickevicius, Audrius Snieckus

Summary: The purpose of this study was to identify differences in hamstring passive stiffness between the pre-season and in-season periods. Hamstring strength and passive stiffness were measured in professional male soccer players before and after the pre-season (4 weeks), and after the in-season (6 weeks) periods using an isokinetic dynamometer. Muscle passive stiffness was determined from the slope of the passive torque-angle relationship. External loads (acceleration and jumps) were monitored by GPS and internal loads by questionnaire. Hamstring passive stiffness increased after 10 weeks of training and matches, without changes in passive peak torque and range of motion. The hamstring passive stiffness modifications were associated with the volume and intensity of accelerations and jumps. The individual data analysis also provided some support for the suppression of the biomechanical adaptation in the subjects with relatively large external load. Regular training and match workouts increase hamstring passive stiffness in professional soccer players but the adaptation of muscle-tendon unit passive elements might not occur if players experience excessive mechanical stress. 



#12 Asymmetry Thresholds for Common Screening Tests and Their Effects on Jump Performance in Professional Soccer Players 

Reference: J Athl Train. 2020 Dec 2. doi: 10.4085/1062-6050-0013.20. Online ahead of print. 

Authors: Paul J Read, Seán McAuliffe, Chris Bishop, Jon L Oliver, Phil Graham-Smith, Mohammed Abdulaziz Farooq

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Summary: Arbitrary asymmetry thresholds are regularly used in professional soccer athletes, notwithstanding the sparse literature available to examine their prevalence. The aim was to establish normative and positional asymmetry values for commonly used screening tests and investigate their relationships with jumping performance. A total of 203 professional male soccer players participated in this study. Bilateral and unilateral jumping; range of motion; and hamstrings (HAM), quadriceps (QUAD), and hip-adductor and -abductor strength tests were used to quantify asymmetry. Players were divided into 4 quartiles (Q1-Q4) based on the magnitude of their asymmetry for each test. Single composite scores were also developed to group tests by range of motion and HAM, QUAD, hip-adduction, and hip-abduction strength, and differences in jump performance were examined among players in each quartile. Large variability (range = 5.2%-14.5%) was evident in asymmetry scores across the different tests and physical qualities. Forwards displayed greater asymmetry in concentric quadriceps and eccentric hip-abduction strength (P < .05). The HAM and QUAD composite scores indicated that Q4 players jumps were shorter than than in other quartiles during a single-legged countermovement jump and 10-second hop (P < .05). No decrements in unilateral jump performance were shown among players in each quartile for range of motion or hip-adduction and -abduction strength, and no composite measures of asymmetry affected bilateral jump performance. No single asymmetry threshold was present for all tests; the outcomes were task, variable, and population specific. Larger asymmetries in HAM and QUAD strength appeared to be detrimental to unilateral jump performance. 



#13 Cardiac Structure and Function in Elite Female and Male Soccer Players 

Reference: JAMA Cardiol. 2020 Dec 2;e206088. doi: 10.1001/jamacardio.2020.6088. Online ahead of print. 

Authors: Timothy W Churchill, Bradley J Petek, Meagan M Wasfy, James S Guseh, Rory B Weiner, Tamanna K Singh, Christian Schmied, Hughie O'Malley, George Chiampas, Aaron L Baggish

Summary: Population-specific normative data are essential for the evaluation of competitive athletes. At present, there are limited data defining normal electrocardiographic (ECG) and echocardiographic values among elite US soccer players. The objective was to describe ECG and echocardiographic findings in healthy elite US soccer players. This cross-sectional study analyzed Fédération Internationale de Football Association-mandated screening sessions performed at US Soccer National Team training locations from January 2015 to December 2019. US women's and men's national team soccer players undergoing mandated cardiovascular screening were included. Normal training-related and abnormal ECG findings were reported using the International Recommendations for Electrocardiographic Interpretation in Athletes. Echocardiographic measurements of structural and functional parameters relevant to cardiovascular remodeling were assessed relative to American Society of Echocardiography guideline-defined normal ranges. A total of 238 athletes (122 [51%] female; mean [SD] age, 20 [4] years; age range, 15-40 years) were included. Male athletes demonstrated a higher prevalence of normal training-related ECG findings, while female athletes were more likely to have abnormal ECG patterns (14 [11%] vs 0 in male cohort), largely accounted for by abnormal T-wave inversions. Echocardiography revealed no pathologic findings meeting criteria for sport restriction, but athletes frequently exceeded normal ranges for structural cardiac parameters responsive to exercise-induced remodeling including body surface area-indexed left ventricular (LV) mass (58 of 113 female athletes [51%] and 67 of 114 male athletes [59%]), indexed LV volume (89 of 115 female athletes [77%] and 76 of 111 male athletes [68%]), and LV wall thickness (37 of 122 female athletes [30%] and 47 of 116 male athletes [41%]). Age-stratified analysis revealed age-dependent increases in LV wall thickness, mass, and volumes among female athletes and LV wall thickness and mass among male athletes. These data represent the first set of comprehensive normative values for elite US soccer players and one of the largest sport-specific echocardiographic remodeling studies in female athletes. Abnormal ECG findings were more common in female athletes, while both female and male athletes frequently exceeded clinical normality cut points for remodeling-associated echocardiographic parameters. 



#14 Football (soccer)-related spinal cord injury-reported cases from 1976 to 2020 

Reference: Spinal Cord Ser Cases. 2020 Nov 30;6(1):106. doi: 10.1038/s41394-020-00360-8. 

Authors: Manoj K Poudel, Andrew L Sherman

Summary: The aim was to analyze the existing data on soccer (international football)-related spinal cord injury (SCI). Cases of soccer (international football)-related SCI that were reported globally. Fourteen cases of football-related SCI that occurred between 1976 and 2020 were found. Average age at the time of injury was 19 and 86% of individuals were males. Eight of 14 individuals had vertebral fracture/dislocation, whereas two individuals had concomitant traumatic brain injury. Neurologically, 54% had tetraplegia, 39% had paraplegia, and 8% each suffered from hemiplegia and sensory deficit. Two cases could regain ability to walk with orthosis and four had full mobility with "Return to Play" (RTP). The mortality was 14%. Younger males were most commonly affected. The most common etiology, vertebral level of injury, and neurological manifestation was fall, cervical spine, and tetraplegia respectively. More than 50% of the individuals with football-related SCI were able to walk or RTP after rehabilitation. Further studies are required to establish universal RTP criteria and formulate preventive measures. 



#15 The road from the 2018 FIFA World Cup to UEFA EURO 2020 Direction of travel of time zones crossed and results achieved by soccer players

Reference: Res Sports Med. 2020 Nov 29;1-11. doi: 10.1080/15438627.2020.1853545. Online ahead of print. 

Authors: Michał Zacharko, Marek Konefał, Łukasz Radzimiński, Paweł Chmura, Krzysztof Błażejczyk, Jan Chmura, Marcin Andrzejewski 

Summary: The study detailed here has sought to assess the physical and technical activity engaged in by football players in the light of the direction of travel in which time zones were crossed as players transferred from training centres to match venues, in the context of matches played at the 2018 FIFA World Cup in Russia. The material consisted of 945 observations of 340 players. Analysed: total distances covered [km], distances covered with high-intensity running (20-25 km/h) [m], numbers of sprints, numbers of shots, numbers of passes, pass accuracy [%] and the official ranking of national teams. Three categories of time-zone shift (training centre match venue) were taken account of, i.e. (1) WestEast (WE), (2) Same Zone (SZ) and (3) EastWest (EW). Analysis of results revealed that players in the EW and SZ categories were able to achieve results significantly better than those moving WE (total distances covered H = 11.815(2); p = 0.003; numbers of passes H = 7.630(2); p = 0.022), and this in relation to team placings in the end-of-tournament ranking (H = 18.099(2); p = 0.001). The results will be valuable in searching places for training centres during future FIFA World Cup and UEFA European Championship competitions. 


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