Latest research in football - week 43 - 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 Dose-Response Relationship Between External Load and Wellness in Elite Women's Soccer Matches: Do Customized Velocity Thresholds Add Value?
Reference:  Int J Sports Physiol Perform. 2020 Sep 4;1-7. doi: 10.1123/ijspp.2019-0660. Online ahead of print.
Authors: Dawn Scott, Dean Norris, Ric Lovell
Summary: The purpose was to examine the dose-response relationship between match-play high-speed running (HSR), very high-speed running (VHSR), and sprint (SPR) distances versus subsequent ratings of fatigue and soreness. Thirty-six outfield players competing in the professional National Women's Soccer League (NWSL, United States) with a minimum of five 90-minute match observations were monitored during the 2016 and 2017 seasons (408 match observations, 11 [6]/player). HSR (≥3.47 m·s-1), VHSR (≥5.28 m·s-1), and SPR (≥6.25 m·s-1) were determined generically (GEN) in players using a 10-Hz global positioning system. HSR, VHSR, and SPR speed thresholds were also reconfigured according to player peak speed per se and in combination with the final velocity achieved in the 30:15 Intermittent Fitness Test (locomotor approach to establishing individual speed zones). On the morning following matches (match day [MD + 1]), players recorded subjective wellness ratings of fatigue and soreness using 7-point Likert scales. Fatigue (-2.32; 95% CI, -2.60 to -2.03 au; P < .0001) and soreness (-2.05; 95% CI, -2.29 to -1.81; P < .0001) ratings worsened on MD + 1. Standardized unit changes in HSRGEN (fatigue: -0.05; 95% CI, -0.11 to 0.02 and soreness: -0.02, 95% CI, -0.07 to 0.04) and VHSRGEN (fatigue: -0.06; 95% CI, -0.12 to 0.00 and soreness: -0.04; 95% CI, -0.10 to 0.02) had no influence on wellness ratings at MD + 1. Individualized speed thresholds did not improve the model fit. Subjective ratings of fatigue and wellness are not sensitive to substantial within-player changes in match physical performance. HSR, VHSR, and SPR thresholds customized for individual players' athletic qualities did not improve the dose-response relationship between external load and wellness ratings.

#2 The use of recovery strategies by Spanish first division soccer teams: a cross-sectional survey
Reference: Phys Sportsmed. 2020 Sep 3. doi: 10.1080/00913847.2020.1819150. Online ahead of print.
Authors: Albert Altarriba-Bartes, Javier Peña, Jordi Vicens-Bordas, Martí Casals, Xavier Peirau, Julio Calleja-González
Summary: Different active and passive post-exercise recovery techniques such as massage, foam rolling, stretching or ice baths among others, are used by elite athletes to promote effective physiological, physical, and mental restoration. However, limited research is available investigating the use of recovery strategies in professional soccer. As such, we aimed to explore and describe the use of strategies by professional teams throughout the season, describing competitive and preparatory phases. The present study collected data from all professional Spanish soccer teams who played in "LaLiga" (The Spanish first division), during the season 2018-2019 (n=20) and the ones promoted for the season 2019-2020 (n=3). A six-section online survey was responded once. Teams used different recovery protocols and combinations, although natural and physical strategies such as sleep/nap, food/fluid replacement, cold/ice bath/shower/immersion, and massage were always present. However, there is no agreement in the protocols and timings employed. Three physical strategies showed a higher presence in the recovery protocols after competition: cold/ice bath/shower/immersion, massage and foam rolling; always used by seventeen teams (74%), sixteen (70%) and thirteen (57%) respectively. The design and supervision of recovery are multidisciplinary tasks in 87% of the teams. Our findings also demonstrate that although there is a body of scientific evidence on recovery, a gap between theory and practice exists with 13% of the teams acknowledging that insufficient logistics and economic resources limit the use of some strategies, and two teams (9%) not periodizing or individualizing recovery. The investigation provided insight into the current use of recovery strategies by "LaLiga" teams, highlighting that all clubs used them to one extent or another, but also that significant variability responding to individualized perceptions exists. Moreover, this study provides relevant contextual information that may be useful for professional soccer staff concerning the use of recovery strategies.

#3 Differences in GPS variables according to playing formations and playing positions in U19 male soccer players
Reference: Res Sports Med. 2020 Sep 3;1-15. doi: 10.1080/15438627.2020.1815201. Online ahead of print.
Authors: Stefano Borghi, Davide Colombo, Antonio La Torre, Giuseppe Banfi, Matteo Bonato, Jacopo Antonino Vitale
Summary: The aims of this study were 1) to investigate Global Positioning System (GPS)-based match physical performance according to players' playing position in three different playing formations (4-4-2, 3-5-2, 4-3-3) and 2) to analyse the differences in match performance between 1st and 2nd half. Twenty-three U19 elite male soccer players (age: 18 ± 1 year, height: 1.80 ± 0.04 m, body mass: 70.65 ± 6.02 kg), categorized as Central Back (CB, n = 5), Full Back (FB, n = 4), Central Midfielders (CM, n = 4), Wingers (W, n = 3), Strikers (S, n = 7), were monitored using 10 Hz GPS during 31 competitive matches. The results showed that FB and W always had the highest very high-speed running distance and number of sprints in all playing formations. Significant decrease in all GPS variables was observed in the 2nd half of the match for all playing positions. Strength coaches should adopt specific training regimes in accordance with players' playing position.

#4 Using Optical Tracking System Data to Measure Team Synergic Behavior: Synchronization of Player-Ball-Goal Angles in a Football Match
Reference: Sensors (Basel). 2020 Sep 3;20(17):E4990. doi: 10.3390/s20174990.
Authors: Daniel Carrilho, Micael Santos Couceiro, João Brito, Pedro Figueiredo, Rui J Lopes, Duarte Araújo
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Summary: The ecological dynamics approach to interpersonal relationships provides theoretical support to the use of kinematic data, obtained with sensor-based systems, in which players of a team are linked mainly by information from the performance environment. Our goal was to capture the properties of synergic behavior in football, using spatiotemporal data from one match of the 2018 FIFA WORLD CUP RUSSIA, to explore the application of player-ball-goal angles in cluster phase analysis. Linear mixed effects models were used to test the statistical significance of different effects, such as: team, half(-time), role and pitch zones. Results showed that the cluster phase values (synchronization) for the home team, had a 3.812×10-2±0.536×10-2 increase with respect to the away team (X2(41)=259.8,&nbsp;p<0.001) and that changing the role from with ball to without ball increased synchronization by 16.715×10-2±0.283×10-2 (X2(41)=12227.0,&nbsp;p<0.001). The interaction between effects was also significant. The player-team relative phase, the player-ball-goal angles relative frequency and the team configurations, showed that variations of synchronization might indicate critical performance changes (ball possession changes, goals scored, etc.). This study captured the ongoing player-environment link and the properties of team synergic behavior, supporting the use of sensor-based data computations in the development of relevant indicators for tactical analysis in sports.

#5 Football and COVID-19 risk: correlation is not causation
Reference: Clin Microbiol Infect. 2020 Sep 3;S1198-743X(20)30517-6. doi: 10.1016/j.cmi.2020.08.034. Online ahead of print.
Authors: Fares Ayoub, Toshiro Sato, Atsushi Sakuraba
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#6 Strength Conditioning Program to Prevent Adductor Muscle Strains in Football: Does it Really Help Professional Football Players?
Reference: Int J Environ Res Public Health. 2020 Sep 2;17(17):E6408. doi: 10.3390/ijerph17176408.
Authors: Javier F Núñez, Ismael Fernandez, Alberto Torres, Sergio García, Pablo Manzanet, Pascual Casani, Luis Suarez-Arrones
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Summary: Coaches at the professional level are often concerned about negative side effects from testing and intensive resistance training periods, and they are not willing to base their training prescriptions on data obtained from semiprofessional or amateur football players. Consequently, the purpose of this study was to analyze the reliability and effectiveness of two adductor injury active prevention programs using the adductor/abductor ratio and deficit between legs, on the basis of adduction-abduction power output during the exercises proposed, in professional football players. Forty-eight professional football players undertook complementary strength training for the adductor and abductor muscles in their dominant and non-dominant legs, once or twice a week throughout the playing season. The volume of the session was determined by the adductor/abductor ratio and the deficit between legs in the last session training measured. The number and severity of muscle injuries per 1000 h of exposure were recorded. Both prevention programs showed a very low rate of adductor injury (0.27 and 0.07 injuries/1000 h) with mild-to-moderate severity, maintaining a balance in percentage asymmetry between dominant and non-dominant legs for adductor (10.37%) and in the adductor/abductor ratio (0.92) in top professional football players throughout the season. The strength conditioning program proposed can help to prevent adductor muscle injuries in top professional football players.

#7 An Investigation into the Relationship Between Heart Rate Recovery in Small-Sided Games and Endurance Performance in Male, Semi-professional Soccer Players
Reference: Sports Med Open. 2020 Sep 10;6(1):43. doi: 10.1186/s40798-020-00273-8.
Authors: Lars Reinhardt, Stephan Schulze, Eduard Kurz, René Schwesig
Summary: The ability to recover in the shortest possible time plays an important role especially in intermittent sports such as soccer. Evidence suggests that a well-developed endurance performance has positive effects on the repeated-sprint ability and thus also on the short-term recovery. However, it has not been clarified whether these relationships still exist in a soccer-specific situation. Therefore, the purpose of this investigation was to evaluate the ability of semi-professional soccer players to recover during standardized small-sided games (SSGs) as an endurance performance indicator. Eighteen male semi-professional soccer players (age, 23.5 ± 3.7 years) performed an incremental treadmill test (ITT) to determine their running velocity and heart rate at a fixed lactate threshold of 4 mmol L-1 (v4). Two days later, the players carried out six bouts of 4 vs. 4 SSGs (duration, 90 s; load to rest ratio, 1:1). A GPS-based tracking system was used to determine distances covered at four fixed speed zones (i.e., < 7.2 km/h, 7.2-14.4 km/h, 14.4-19.8 km/h, > 19.8 km/h) and total distance covered during the SSGs. Furthermore, the frequency of occurrence of accelerations (> 1.54 m s-2) was calculated. SSGs' internal load was quantified by average heart rate and blood lactate concentration after the SSGs. Their recovery ability was evaluated using heart rate recovery (HRR) after the last bout of the SSGs. A very large correlation (r = - .91) with an explained variance of 84% was found between HRR and v4. Further, a better performance in the ITT was also related with a higher number of accelerations executed during SSGs (r = .60). The total distance and distances in predefined speed zones did not show any association to v4. This study showed a strong relationship between HRR after standardized 4 vs. 4 SSGs and the soccer players' endurance performance in a laboratory setting. Thus, besides being associated with endurance capacity, v4 seems sufficient to evaluate the sport-specific ability to recover in soccer players.

#8 Effects of Plyometric Jump Training on Jump and Sprint Performance in Young Male Soccer Players: A Systematic Review and Meta-analysis
Reference: Sports Med. 2020 Sep 11. doi: 10.1007/s40279-020-01337-1. Online ahead of print.
Authors: Rodrigo Ramirez-Campillo, Daniel Castillo, Javier Raya-González, Jason Moran, Eduardo Sáez de Villarreal, Rhodri S Lloyd
Summary: Even from a young age, modern soccer requires high levels of physical fitness development, particularly jumping and sprinting. Plyometric jump training (PJT), combined with young athletes' regular soccer sessions, has the potential to improve jumping and sprinting. However, studies exploring the effects of PJT are generally limited by small sample sizes. This problem of underpowered studies may, thus, be resolved by pooling study results in a meta-analysis. The objective of this systematic review with meta-analysis (SRMA) was to assess the effects of plyometric jump training (PJT) on jumping and sprinting among young male soccer players. The SRMA included peer-reviewed articles that incorporated PJT in healthy players (i.e., < 23 years of age), a control group, and a measure of jumping or sprinting. Means and standard deviations of outcomes were converted to Hedges' g effect sizes (ES), using the inverse variance random-effects model. Moderator analyses were conducted for PJT duration, frequency, total number of sessions, participants' chronological age, and FIFA age categories (i.e., U-17 vs. U-20 vs. U-23). A multivariate random-effects meta-regression was also conducted. Thirty-three studies were included, comprising 1499 participants. PJT improved vertical jump tests (ES = 0.60-0.98; all p < 0.01) and linear sprint performance (ES = 0.60-0.98; p < 0.03). Interventions of > 7 weeks and > 14 PJT sessions induced greater effects compared to PJT with ≤ 7 weeks and ≤ 14 total sessions on 10-m sprint performance (between group p = 0.038). PJT is effective in improving jumping and sprinting performance among young male soccer players. Greater 10-m linear sprinting improvements were noted after interventions > 7-week duration and > 14 sessions, suggesting a greater return from exposure to longer PJT interventions, partially in support for the adoption of a long-term approach to athletic development in young athletes. However, with reference to the findings of the meta-regression, and those from the remaining subgroup and single factors analysis, a robust confirmation regarding the moderator role of participant's age or PJT configuration effects on young soccer player's fitness qualities needed.

#9 Anthropometric and physical performance profiling does not predict professional contracts awarded in an elite Scottish soccer academy over a 10-year period
Reference: Eur J Sport Sci. 2020 Sep 4;1-10. doi: 10.1080/17461391.2020.1808079. Online ahead of print.
Authors: Thomas P Craig, Paul Swinton
Summary: The purpose of this long-term retrospective analysis was to determine whether anthropometric and physical performance data could predict success in elite youth Scottish soccer players. Stature, body mass, sprint, jump and aerobic performance were collected from 512 players (U10 to U17) across a 10-year period. Players participated in an average of four profiling sessions (range: 1-14) and up to a maximum of three per year (August, December, and May) with standardisation applied to the surface, test order, time and protocols. One hundred players were awarded professional contracts. Associations between variables were quantified with mixed-effects linear models. Prediction was assessed with least absolute shrinkage and selection operator (LASSO) regression developed on a training set (2/3 data) and tested with proportion of error on a leave-out (1/3 data) test set. Confidence intervals were obtained through bootstrap LASSO samples. A strong relative age bias was identified with 50% of successful players born in the first quarter of the year. Successful players were on average taller and performed better in sprint and jump tests (p < 0.05). However, effects were small and even when variables were combined, proportion of errors identified were similar to random guessing (0.45[95%CI:0.41-0.49]). The results indicate that whilst successful players as youths demonstrate on average distinct anthropometric and physical profiles, these differences are unlikely to provide a reliable source to predict success within an already talented group. Practitioners should use data collected to guide exercise prescription but be aware of its substantive limitations in predicting success in isolation. Using robust statistical procedures, researchers and practitioners within soccer academies that are continually collecting data should assess whether accurate predictions can be made combining data across a holistic range of dimensions including physiological, technical, psychological, tactical skills and expertise from technical coaches. Academies should consider processes such as coach and scout education programmes to reduce the negative impacts of controllable factors such as the RAE. There are limitations of using anthropometric and physical performance profiling data to predict who will become a successful player. The information is still an important part of the talent development process with data being used to assist the creation and individual tailoring of physical training and appropriate recording and monitoring is encouraged.

#10 Injury Analysis in Professional Soccer by Means of Media Reports - Only Severe Injury Types Show High Validity
Reference: Open Access J Sports Med. 2020 Aug 7;11:123-131. doi: 10.2147/OAJSM.S251081. eCollection 2020.
Authors: Volker Krutsch, Stephan Grechenig, Oliver Loose, Leonard Achenbach, Johannes Zellner, Heiko Striegel, Volker Alt, Johannes Weber, Markus Braun, Stephan Gerling, Werner Krutsch
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Summary: Injury data of professional soccer players obtained from media reports are frequently used in scientific research, but the accuracy of such data is still unclear. Injuries of professional soccer players of the German first and second league were documented by continuously screening media reports over one season (2015-2016). After the season, the validity of media-reported injuries was anonymously analyzed by the team physicians of 8 different soccer clubs. A total of 255 injuries of 240 players of 8 professional soccer teams had been published online, of which 146 were confirmed by the team doctors as correct, yielding a rate of 57.3% of confirmed media-reported injuries. In addition, 92 injuries without media registration were detected and added to the online statistics, resulting in 347 injuries and an overall weak validity of media-based data of 42.1%. Statistical analysis showed that the validity of media-reported injury data depended on both the individual soccer club and the body site affected by injury: publications on knee injuries (78.2%) had a higher validity than those on foot injuries (46.2%), and publications on severe injuries had a higher validity (joint dislocation: 100%; ligament rupture: 82.9%; fracture: 73.3%) than those on minor injuries. Publications on specific severe soccer injuries, such as anterior cruciate ligament (ACL) injuries, had a validity of 100%. Media-based injury data were only valid for a few severe injury types such as ACL injuries. In daily soccer routine and scientific research, media-based data should thus only be used in combination with specific criteria or verification processes.

#11 Comparison of symptomatic spondylolysis in young soccer and baseball players
Reference: J Orthop Surg Res. 2020 Sep 3;15(1):378. doi: 10.1186/s13018-020-01910-4.
Authors: Takuji Yokoe, Takuya Tajima, Hiroshi Sugimura, Shinichirou Kubo, Shotarou Nozaki, Nami Yamaguchi, Yudai Morita, Etsuo Chosa
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Summary: Spondylolysis is the main cause of low back pain (LBP) in young athletes. There are few studies analyzing the difference of spondylolysis among young athletes with different sports activities. The purpose of this study was to compare the clinical factors and distribution of the lesions of spondylolysis on magnetic resonance imaging (MRI) scans in young soccer and baseball players with symptomatic spondylolysis. The medical records of 267 young athletes aged 7 to 18 years old who underwent MRI to evaluate the cause of LBP between 2017 and 2020 were retrospectively reviewed to identify patients with spondylolysis. Of the young athletes with symptomatic spondylolysis, clinical factors and MRI findings in soccer and baseball players were retrospectively evaluated. The clinical factors were age, sex, interval from onset of LBP to MRI, and side of the dominant leg in the sports field. MRI findings included number, lumbar level, and side of the lesions. A total of 33 soccer players (mean age, 15.4 ± 1.4 years) and 49 baseball players (mean age, 15.4 ± 1.6 years) with symptomatic spondylolysis were enrolled. All patients were male. No significant differences were noted in age and the interval from onset of LBP to MRI between the groups. Soccer players had greater numbers of multiple (p < 0.001) and bilateral (p < 0.001) lesions than baseball players. The dominant side of the hand for pitching or batting was correlated with the contralateral-side lesions in baseball players (p = 0.001). The distribution of the lesions of spondylolysis differed in young soccer and baseball players. Pitching or batting with the dominant-side hand would be associated with contralateral-side lesions in baseball players. Sports-specific movements and the side of the dominant leg should be considered when treating young athletes with symptomatic spondylolysis.

#12 Heading in the right direction: A critical review of studies examining the effects of heading in soccer players
Reference: J Neurotrauma. 2020 Sep 3. doi: 10.1089/neu.2020.7130. Online ahead of print.
Authors: Taylor Snowden, Hannah Reid, Samantha Kennedy, Rebecca A Kenny, Amanda McQuarrie, Lynneth Stuart-Hill, Mauricio Garcia-Barrera, Jodie Gawryluk, Brian Ross Christie
Summary: The practice of heading in soccer has become a public concern due to the potential for subconcussive impacts to cause cumulative concussive-like effects; however experimental evidence for this hypothesis has been mixed. This systematic review used pre-defined search parameters to assess primary literature that examined changes in cognitive, behavioural, structural and/or biological processes after acute heading exposure in youth and young adult soccer players. The findings were synthesized into a concise and comprehensive summary of the research following the preferred reporting items for systematic reviews and meta-analyses (PRISMA) format, and suggestions for standardization of acute heading protocols are described. A total of 1189 articles were considered for this review, with 19 articles meeting all of the inclusion criteria for full analysis. An attempt was made to identify methods with significant sensitivity and reliability by grouping studies based on their outcome measures. Due to lack of standardization across intervention types and data collection protocols, no sensitive and reliable methods could be conclusively identified to assess the effects of acute heading exposure in soccer players. Based on this review, there is not enough evidence to either support or refute the potential of effects of subconcussive events from acute soccer heading exposure. Recommendations for standardization of acute heading exposure studies based on the included literature are discussed. Standardization is required to better understand the impact of acute heading exposure in soccer players, while allowing for the development of guidelines that mitigate any potential risks and allowing athletes to remain active and develop their skills.

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