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Latest research in football - week 30 - 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 Phase Angle Is Related to 10 m and 30 m Sprint Time and Repeated-Sprint Ability in Young Male Soccer Players

Reference: Int J Environ Res Public Health.  2021 Apr 21;18(9):4405.  doi: 10.3390/ijerph18094405.

Authors: Priscila Custódio Martins, Anderson Santiago Teixeira, Luiz Guilherme Antonacci Guglielmo, Juliana Sabino Francisco, Diego Augusto Santos Silva, Fábio Yuzo Nakamura, Luiz Rodrigo Augustemak de Lima

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Summary: The aim was to examine the association between phase angle (PhA) and bioelectrical impedance vector analysis (BIVA) and components of physical performance in male youth soccer players. Sixty-two players from two professional soccer academies were recruited. Electrical bioimpedance was used to obtain the PhA and BIVA. Body fat (BF) and lean soft tissue mass (LSTM) were measured by dual-energy X-ray absorptiometry. All players completed physical tests including the standing long jump (SLJ), Carminatti's test (peak speed at the end of the test, PST-CAR), 10 m and 30 m straight-line sprints, and repeated-sprint ability (RSA) test (RSAbest and RSAmean times). Adjusting for chronological age, BF, and LSTM, multiple regression analysis outputs showed that PhA remained inversely related to RSAmean (β = -0.362; p < 0.001), RSAbest (β = -0.239; p = 0.020), 10 m (β = -0.379; p = 0.012), and 30 m (β = -0.438; p < 0.001) sprint times, while the association with PST-CAR and SLJ performance were statistically non-significant. In addition, BIVA showed that differences in confidence ellipses were found between athletes in the reference population and the study sample (p < 0.05). The tolerance ellipses indicated that the athletes in the present study had more total body water (TCW) and lower proportions of intracellular water (ICW) to extracellular water (ECW). The reference population had more TCW and ICW/ECW. Our results suggest that young soccer players with higher PhA values, indicating better cell integrity and functionality, have better performance in typical anaerobic running activities, such as sprinting speed and RSA performance, adjusted to age and body composition characteristics.



#2 Match Analysis of Soccer Refereeing Using Spatiotemporal Data: A Case Study

Reference: Sensors (Basel). 2021 Apr 5;21(7):2541.  doi: 10.3390/s21072541.

Authors: Bruno Gonçalves, Diogo Coutinho, Bruno Travassos, João Brito, Pedro Figueiredo

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Summary: This case study explored how spatiotemporal data can develop key metrics to evaluate and understand elite soccer referees' performance during one elite soccer match. The dynamic position of players from both teams, the ball and three elite referees allowed to capture the following performance metrics: (i) assistant referees: alignment with the second last defender; (ii) referee: referee diagonal movement-a position density was computed and a principal component analysis was carried to identify the directions of greatest variability; and (iii) referee: assessing the distance from the referee to the ball. All computations were processed when the ball was in-play and separated by 1st and 2nd halves. The first metric showed an alignment lower than 1 m between the assistant referee and the second last defender. The second metric showed that in the 1st half, the referee position ellipsis area was 548 m2, which increased during the 2nd half (671 m2). The third metric showed an increase in the distance from the referee to the ball and >80% of the distance between 5-30 m during the 2nd half. The findings may be used as a starting point to elaborate normative behavior models from the referee's movement performance in soccer.



#3 Comparative Analysis of Soccer Performance Intensity of the Pre-Post-Lockdown COVID-19 in LaLiga™

Reference: Int J Environ Res Public Health. 2021 Apr 1;18(7):3685.  doi: 10.3390/ijerph18073685.

Authors: Abraham García-Aliaga, Moisés Marquina, Antonio Cordón-Carmona, Manuel Sillero-Quintana, Alfonso de la Rubia, Ignacio Refoyo Román 

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Summary: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) forced a stoppage in the 2019/2020 season of LaLiga™, possibly influencing performance indicators in the return to competition. Therefore, here, we evaluated whether the stoppage due to the coronavirus 2019 disease (COVID-19) lockdown influenced physical performance compared to the start of LaLigaTM in terms of high-intensity efforts. Using a semi-automatic, multiple-camera system, running activities during 22 matches were analyzed. We compared the first 11 matches of the season (pre-lockdown) with the 11 matches just after the restart of LaLiga™ (post-lockdown). The results showed higher (p < 0.05) performance in the pre-lockdown period compared with the post-lockdown period, including in medium-speed running (14.1-21 km/h), high-speed running (21.1-24 km/h), and sprinting speed running distances (>24 km/h). However, the number of accelerations/min and decelerations/min were significantly higher during the post-lockdown period. Therefore, we conclude that the stoppage due to the COVID-19 lockdown generated lower physical performance in the post-lockdown period compared with the pre-lockdown period, most likely due to the accumulation of matches (congested schedules).



#4 Effectiveness of the FIFA 11+ Referees Injury Prevention Program in reducing injury rates in male amateur soccer referees

Reference: Scand J Med Sci Sports. 2021 Apr 29.  doi: 10.1111/sms.13983. Online ahead of print.

Authors: Wesam Saleh A Al Attar, Mario Bizzini, Fahad Alkabkabi, Nasser Alshamrani, Saud Alarifi, Hosam Alzahrani, Hussain Ghulam, Eman Aljedaani, Ross H Sanders

Summary: The Fédération International de Football Association (FIFA) 11+ Referees Injury Prevention Program (FIFA 11+ Referees Program) is a structured warm-up program specially designed to prevent injuries in soccer referees. However, its effectiveness has yet to be fully documented in the literature. Therefore, the purpose of this study was to investigate the effectiveness of the FIFA 11+ Referees Program in reducing injury rates among soccer referees. A cluster randomized controlled trial was conducted. Two hundred male amateur soccer referees (mean±SD age, 31.6±4.1 years) participated in this study. Participants were randomly allocated to the experimental and control groups. The experimental group performed the FIFA 11+ Referees Program as a warm-up during training sessions at least twice a week, and the control group performed their usual warm-ups. The participants were followed up for one season. The outcome measures were the incidence of overall injury, initial injury, recurrent injury, injury mechanism, and injury severity (primary), and the rate of adherence to the intervention program (secondary). A total of 24 injuries were reported among 100 referees in the control group in 16606 hours of exposure (1.45 injuries/1000 exposure hours), and a total of nine injuries were reported across 100 referees within the experimental group in 17834 exposure hours (0.50 injuries/1000 exposure hours). The Injury Risk Ratio (IRR) was 0.35 (95% CI 0.26 to 0.45). The results indicated that the FIFA 11+ Referees Program effectively reduced injuries in the experimental group by 65% compared to the control group.



#5 The Influence of Playing Formation on Physical Demands and Technical-Tactical Actions According to Playing Positions in an Elite Soccer Team

Reference: Int J Environ Res Public Health. 2021 Apr 14;18(8):4148.  doi: 10.3390/ijerph18084148.

Authors: José Luis Arjol-Serrano, Miguel Lampre, Adrián Díez, Daniel Castillo, Fernando Sanz-López, Demetrio Lozano

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Summary: The aim of this study was to examine the differences in the physical demands and technical-tactical actions encountered by soccer players between two playing formations (1-4-2-3-1 and 1-4-4-2) for each playing position. Twenty-three professional male soccer players who played 31 official matches participated in this study. Players were classified according to their playing position: central defenders (CD), wide defenders (WD), central midfielders (CM), wide midfielders (WM), offensive midfielders (OM) and forwards (FW). The physical demands were collected as total distance (TD), distance covered in different speed thresholds, and number of accelerations and decelerations. Also, the technical-tactical variables were recorded. The results showed that the 1-4-2-3-1 playing formation demanded decelerations between 2-4 m·s2 (p = 0.027; ES = 0.26) in comparison with 1-4-4-2 for all players. Likewise, forwards (FW) and central midfielders (CM) registered higher physical demands playing with the 1-4-2-3-1 compared to the 1-4-4-2 formation. Regarding the technical-tactical actions, they showed differences between the playing positions of the two playing formations. The findings suggest coaches prescribe specific training programs based on the influence of the playing formation and playing position on the physical demands and technical-tactical actions encountered by players during official match-play.



#6 Muscle Damage and Performance after Single and Multiple Simulated Matches in University Elite Female Soccer Players

Reference: Int J Environ Res Public Health. 2021 Apr 14;18(8):4134.  doi: 10.3390/ijerph18084134.

Authors: Tai-Ying Chou, Kazunori Nosaka, Trevor C Chen

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Summary: The present study aimed to compare changes in muscle damage and performance parameters after playing single versus multiple soccer matches to examine fixture congestion effects on performance. Twelve elite female university soccer players performed single, three and six consecutive 90-min bouts of the Loughborough Intermittent Shuttle Test (LIST) with ≥12-weeks between conditions in a pseudo-randomized order. Heart rate, blood lactate, rating of perceived exertion and covering distance in each LIST were examined. Changes in several types of muscle damage (e.g., maximal voluntary isometric torque of the knee extensors: MVC-KE) and performance measures (e.g., Yo-Yo Intermittent Recovery Test level 1: YYIR1) were taken before each LIST, 1 h, and 1-5 d after the last LIST. The total distance covered during the LIST was shorter (p < 0.05) in the 2nd-3rd, or 2nd-6th LISTs when compared with the 1st LIST. Changes (p < 0.05) in all measures were observed after the LIST, and the greatest changes were observed after the six than after the three LISTs followed by one LIST (e.g., largest changes in MVC-KE: -26 > -20 > -14%; YYIR1: -31 > -26 > -11%). Many of the variables did not recover to the baseline for 5 d after six LISTs. These suggest that fixture congestion induces greater muscle damage and performance decline than a single match.



#7 Comparison Between Soccer and Basketball of Bone Bruise and Meniscal Injury Patterns in Anterior Cruciate Ligament Injuries

Reference: Orthop J Sports Med. 2021 Apr 14;9(4):2325967121995844.  doi: 10.1177/2325967121995844. eCollection 2021 Apr.

Authors: Huijuan Shi, Li Ding, Yanfang Jiang, Haocheng Zhang, Shuang Ren, Xiaoqing Hu, Zhenlong Liu, Hongshi Huang, Yingfang Ao

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Summary: The varying effectiveness of anterior cruciate ligament (ACL) injury prevention programs between soccer and basketball may be due to differences in sport-specific injury mechanisms. Bone bruise patterns may provide information regarding injury mechanisms. The aim was to compare bone bruise and meniscal injury patterns for ACL injuries sustained in soccer versus basketball. Clinical notes, operative reports, and magnetic resonance imaging scans were reviewed for patients who sustained a noncontact ACL rupture while playing soccer or basketball between August 2016 and August 2018. The presence, location, and signal intensity of bone bruises on the tibia and femur were documented, and patterns were classified according to the location of the bone bruise in the lateral-medial direction. The meniscal and bone bruise injury patterns and the specific bone bruise locations were compared between the soccer and basketball groups. Overall, 138 patients were included (56 with soccer-related and 82 with basketball-related ACL injury). No significant difference between the groups was observed in bone bruise patterns (P = .743) or meniscal injury patterns (P = .952). Bone bruise on the lateral side only of both the femur and the tibia was the most common pattern in both soccer (41.9%) and basketball (47.0%) groups; the most common meniscal injury type was an isolated lateral meniscal injury in both soccer (50.0%) and basketball (45.0%) groups. For patients with bone bruises on both the lateral and the medial sides of both the femur and the tibia (BF+BT), the bone bruise signal intensity on the lateral side of the femur (P < .001) and tibia (P = .009) was significantly higher than that on the medial side for both groups. The bone bruises on the lateral side of the femur (P < .001) and tibia (P = .002) were significantly more anterior than those on the medial side for patients with the BF+BT pattern. No significant differences in bone bruise location or meniscal injury type were detected when comparing ACL injuries sustained during soccer versus basketball. The study results suggest a similar biomechanical loading pattern for ACL injuries in these sports.



#8 Distribution of Plantar Pressure in Soccer Players

Reference: Int J Environ Res Public Health. 2021 Apr 15;18(8):4173. doi: 10.3390/ijerph18084173.

Authors: Arletta Hawrylak, Anna Brzeźna, Krystyna Chromik

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Summary: The aim of this study was to evaluate differences in the static and dynamic distribution of foot pressure on the ground and to investigate the relationships between body mass index (BMI) and mean variables of plantar pressure between soccer players and their non-athlete peers. The study involved 18 first-division Polish soccer players and 30 non-athlete physiotherapy students. The research experiment was conducted using the FreeMed platform. Basic descriptive statistics were calculated to summarize the variables. Additionally, in the static and dynamic tests, Spearman's rank correlations between body mass index (BMI) and plantar load were calculated. Statistically significant differences between groups were observed in the loading of the dominant limb. A statistically significant correlation between BMI and loading of both limbs was found in the static test and between BMI and loading of the dominant limb in the dynamic test. The baropodometric mat used in our study helped determine the plantar pressure distribution of soccer players and their non-athlete peers. Correlation analysis revealed that BMI was only associated with the mean plantar pressure of the dominant limb in the control group. Further research on a larger group of athletes is needed to determine how much sporting activity may affect the development to modifications within feet in soccer players.



#9 Motor Performance in Male Youth Soccer Players: A Systematic Review of Longitudinal Studies

Reference: Sports (Basel). 2021 Apr 19;9(4):53.  doi: 10.3390/sports9040053.

Authors: Maryam Abarghoueinejad, Adam D G Baxter-Jones, Thayse Natacha Gomes, Daniel Barreira, José Maia

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Summary: The aim of this systematic review was to identify and synthesize the available information regarding longitudinal data addressing young soccer players' motor performance changes. Following the Preferred Reporting Items for Systematic and Meta-analyses (PRISMA) statement, literature searches were performed in three databases: PubMed, ISI Web of Science and SCOPUS. The following descriptors were used: football, soccer, youth, young, player, athlete, physical performance, motor performance, longitudinal. The inclusion criteria were original articles in English with longitudinal data of young males (aged 10-18 years), with the aim to investigate motor performance serial changes. The initial search returned 211 records, and the final sample comprised 32 papers. These papers covered the European continent, and used mixed and pure longitudinal design with variation in sample size and age range. The reviewed studies tended to use different tests to assess the motor performance and aimed to identify changes in motor performance in several ways. In general, they indicated motor performance improvements with age, with a marked influence of biological maturity, body composition, and training stimuli. This review highlights the need for coaches and stakeholders to consider players' motor performance over time whilst considering biological maturation, biological characteristics, and training stimuli.



#10 Can Rules in Technical-Tactical Decisions Influence on Physical and Mental Load during Soccer Training? A Pilot Study

Reference: Int J Environ Res Public Health. 2021 Apr 19;18(8):4313. doi: 10.3390/ijerph18084313.

Authors: Tomás García-Calvo, Juan José Pulido, José Carlos Ponce-Bordón, Miguel Ángel López-Gajardo, Israel Teoldo Costa, Jesús Díaz-García

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Summary: This study aimed to analyze the effects of rules limitations in pass decisions during soccer tasks on physical and mental load reported by players. Participants were 40 semiprofessional Spanish soccer players (Mage = 22.40, SD = 2.25) from two male teams. Two training sessions with four tasks (same tasks with different score system: two maintaining ball possession games with goalkeepers, and two maintaining ball possession games) in counterbalanced order between teams were completed. To achieve a goal during limitation tasks, a minimum number of players had to participate in the passes before the goal. Internal (perceived effort and heart rate) and external physical load (distances), mental load (validated adaptation of the NASA-TXL) and fatigue (VASfatigue) were quantified. Paired t-test and magnitude-based inference were conducted. The results showed significantly higher mean speeds (p < 0.01), effort perception (p < 0.001), and mental fatigue (very likely positive) during possession games with restrictions. Additionally, performance satisfaction obtained significantly higher values with goalkeepers and pass restrictions (very likely positive). External physical load showed no significant differences between situations. The influence of mental fatigue on internal load and the complexity of the tasks could explain these results. Coaches can use this information to manipulate the training load in ecological conditions.



#11 Association between Training Load and Well-Being Measures in Young Soccer Players during a Season

Reference: Int J Environ Res Public Health. 2021 Apr 22;18(9):4451. doi: 10.3390/ijerph18094451.

Authors: Hadi Nobari, Ana Ruivo Alves, Hamed Haghighi, Filipe Manuel Clemente, Jorge Carlos-Vivas, Jorge Pérez-Gómez, Luca Paolo Ardigò

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Summary: This study aimed to analyze the correlations among weekly (w) acute workload (wAW), chronic workload (wCW), acute/chronic workload ratio (wACWR), training monotony (wTM), training strain (wTS), sleep quality (wSleep), delayed onset muscle soreness (wDOMS), fatigue (wFatigue), stress (wStress), and Hooper index (wHI) in pre-, early, mid-, and end-of-season. Twenty-one elite soccer players (age: 16.1 ± 0.2 years) were monitored weekly on training load and well-being for 36 weeks. Higher variability in wAW (39.2%), wFatigue (84.4%), wStress (174.3%), and wHI (76.3%) at the end-of-season were reported. At mid-season, higher variations in wSleep (59.8%), TM (57.6%), and TS (111.1%) were observed. Moderate to very large correlations wAW with wDOMS (r = 0.617, p = 0.007), wFatigue, wStress, and wHI were presented. Similarly, wCW reported a meaningful large association with wDOMS (r = 0.526, p < 0.001); moderate to very large associations with wFatigue (r = 0.649, p = 0.005), wStress, and wHI. Moreover, wTM presented a large correlation with wSleep (r = 0.515, p < 0.001); and a negatively small association with wStress (r = -0.426, p = 0.003). wTS showed a small to large correlation with wSleep (r = 0.400, p = 0.005) and wHI; also, a large correlation with wDOMS (r = 0.556, p = 0.028) and a moderate correlation with wFatigue (r = 0.343, p = 0.017). Wellness status may be considered a useful tool to provide determinant elite players' information to coaches and to identify important variations in training responses.



#12 External Loads in Under-12 Players during Soccer-7, Soccer-8, and Soccer-11 Official Matches

Reference: Int J Environ Res Public Health. 2021 Apr 26;18(9):4581.  doi: 10.3390/ijerph18094581.

Authors: Mario Sanchez, Rodrigo Ramirez-Campillo, Daniel Hernandez, Manuel Carretero, Jesus Maria Luis-Pereira, Javier Sanchez-Sanchez

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Summary: The aim of this study was to compare the external loads (i.e., displacement distances and velocities) of 10-11 years-old soccer players during Soccer-7 (i.e., seven-a-side), Soccer-8 (i.e., eight-a-side), and Soccer-11 (i.e., eleven-a-side) official matches. Male athletes (n = 133; age, 10.9 ± 0.8 years) were measured during official matches for total distance (TD), relative distance (Drel), maximal velocity (Vmax), acceleration (ACC), deceleration (DEC), and absolute and relative distance covered at different velocities. Data during matches were collected using a Global Positioning System unit. Greater TD was recorded during Soccer-11 compared to Soccer-7 and Soccer-8 (p < 0.01), and greater Drel during Soccer-11 compared to Soccer-8 (p < 0.05). Absolute ACC was greater during Soccer-11 compared to Soccer-7 (p < 0.01), although relative values for %ACC and %DEC were greater during Soccer-7 and Soccer-8 compared to Soccer-11 (p < 0.01). Globally, results show that Soccer-11 matches induce greater external loads compared to Soccer-7 and Soccer-8 matches. Current results may help coaches and soccer-related organizers to plan more suited soccer competitions for young players, with lower external loads.



#13 Exploring the Determinants of Repeated-Sprint Ability in Adult Women Soccer Players

Reference: Int J Environ Res Public Health. 2021 Apr 26;18(9):4595. doi: 10.3390/ijerph18094595.

Authors: Lillian Gonçalves, Filipe Manuel Clemente, Joel Ignacio Barrera, Hugo Sarmento, Francisco Tomás González-Fernández, Markel Rico-González, José María Cancela Carral

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Summary: This study aimed to explore the main determinants of repeated-sprint ability (RSA) in women soccer players considering aerobic capacity, sprinting performance, change-of-direction, vertical height jump, and hip adductor/abductor isometric strength. Twenty-two women soccer players from the same team participating in the first Portuguese league were observed. Fitness assessments were performed three times during a 22-week cohort period. The following assessments were made: (i) hip abductor and adductor strength, (ii) squat and countermovement jump (height), (iii) change-of-direction test, (iv) linear sprinting at 10- and 30-m, (v) RSA test, and (vi) Yo-Yo intermittent recovery test level 1. Positive moderate correlations were found between peak minimum RSA and adductor and abductor strength (r = 0.51, p < 0.02 and r = 0.54, p < 0.01, respectively). Positive moderate correlations were also found between peak maximum RSA and adductor and abductor strength (r = 0.55, p < 0.02 and r = 0.46, p < 0.01, respectively). Lastly, a moderate negative correlation was found between fatigue index in RSA and YYIR1 test performance (r = -0.62, p < 0.004). In conclusion, abductor and adductor isometric strength-based coadjutant training programs, together with a high degree of aerobic endurance, may be suitable for inducing RSA in female soccer players.



#14 High Specialization among Female Youth Soccer Players Is Associated with an Increased Likelihood of Serious Injury

Reference: Med Sci Sports Exerc. 2021 Apr 28. doi: 10.1249/MSS.0000000000002693. Online ahead of print.

Authors: Michelle Xiao, Jacie L Lemos, Calvin E Hwang, Seth L Sherman, Marc R Safran, Geoffrey D Abrams

Summary: The purpose was to assess the associations between serious injury (> 3-month time loss) and level of specialization among high-level female soccer players and to compare the specialization and college commitment ages of female youth soccer players to Division I college and professional soccer athletes. Youth, college, and professional female soccer players in the United States playing in the top league at each level were recruited to complete an anonymous online survey. The survey collected information about player demographics, soccer specialization and training patterns, history of serious injuries from soccer, and perceptions surrounding soccer specialization. Comparisons between groups were performed using 2-sample t-tests, chi-squared analyses, and multiple logistic regression models controlling for differences in age. A p-value of less than 0.05 was set as significant. A total of 1,018 (767 youth, 251 college/professional) athletes completed the survey. Serious injuries affected 23.6% of youth and 51.4% of college/professional athletes. Anterior cruciate ligament (ACL) tears were more prevalent in college/professional players compared to youth athletes (18.3% vs 4.0%; p < 0.001). Highly specialized youth athletes (66.5%) were more likely to have sustained a serious injury from soccer compared to athletes with low specialization (Odds Ratio (OR) = 2.28 [1.38-3.92]; p=0.008) but not moderate specialization (OR = 1.37 [0.83-2.27]; p=0.43). A higher proportion of youth athletes specialized at a young age (< 10 years) compared to college/professional players (44.2% vs 25.9%; p < 0.001). High specialization in female youth soccer players is associated with an increased likelihood of sustaining a serious injury. Current youth soccer players are specializing earlier and committing to play college soccer at a younger age compared to when current college and professional players did.






The Coaches’ Efficacy Expectations of Youth Soccer Players with Different Maturity Status and Physical Performance

This study aimed to report possible anthropometrical and physical performance differences between youth soccer players with different maturity status and to report the coaches’ expectations, hypothesizing that coaches would expect more from players with advanced maturity.





Coach Encouragement During Soccer Practices Can Influence Players’ Mental and Physical Loads

This study analyzed the influence of the coaches’ encouragement on the mental and physical load in soccer practices.





Latest research in football - week 29 - 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 Do hip and groin muscle strength and symptoms change throughout a football season in professional male football players? A prospective cohort study with repeated measures

Reference: J Sci Med Sport. 2021 Apr 10;S1440-2440(21)00083-9.  doi: 10.1016/j.jsams.2021.03.019. 

Authors: P van Klij, R Langhout, A M C van Beijsterveldt, J H Stubbe, A Weir, R Agricola, Y Fokker, A B Mosler, J H Waarsing, J Verhaar, I Tak 

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Summary: Groin injuries are common in professional male football and result in significant complaints, time-loss and cost. We aimed to study: 1. Normal values of hip muscle strength and self-reported hip and groin function (Hip And Groin Outcome Score (HAGOS)). 2. Changes in these values throughout the season. 3. If previous (groin) injuries, leg dominance or league were associated with these outcome measures. 313 professional male football players (11 clubs) participated. Player characteristics and previous injuries were registered. Hip muscle strength (hand-held dynamometer) and HAGOS measurements were done at the start, middle and end of the season. Data from 217 players were analysed. Adduction strength (mean±standard deviation, Nm/Kg) was 3.40±0.72 (start), 3.30±0.65 (mid) and 3.39±0.74 (end) (p=0.186). Abduction strength was 3.45±0.67, 3.14±0.57 and 3.28±0.61 (p<0.001). Adduction/abduction ratio was 1.00±0.21, 1.07±0.22 and 1.05±0.23 (p<0.001). Statistically, the HAGOS-subscale 'Pain' (median [interquartile range]) deteriorated slightly during the season (p=0.005), especially from mid-season (97.5 [90.6-100.0]) to end-of-season (95.0 [87.5-100.0]) (p=0.003). Other subscale scores remained unchanged between time points; 85.7 (symptoms), 100.0 (daily living), 96.9 (sports and recreation) 100.0, (physical activities) and 90.0 (quality of life). Previous injuries were associated with lower HAGOS-scores. Dominant legs had higher abduction strength (p<0.001) and lower adduction/abduction ratio (p<0.001). No differences between leagues were found for hip muscle strength and HAGOS-scores. In Dutch male professional football players, hip muscle strength and HAGOS-scores remained relatively stable throughout the season. Pain increased slightly, which while statistically significant, was not clinically relevant.



#2 Influence of the artificial turf certification on physical performance and muscle damage in football players (QUALTURF PROJECT)

Reference: Sci Rep. 2021 Apr 21;11(1):8625.  doi: 10.1038/s41598-021-88192-w.

Authors: Javier Sanchez-Sanchez, Jose Luis Felipe, Antonio Hernandez-Martin, David Viejo-Romero, Vicente Javier Clemente-Suarez, Leonor Gallardo, Jorge Garcia-Unanue

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Summary: This study aimed to analyse the influence of the FIFA Quality PRO certification of artificial turf pitches on the physical, physiological performance and muscle damage in soccer players. Fifteen healthy male players (21.2 ± 1.4 years; 178.2 ± 4.3 cm; 79.1 ± 8.3 kg) from a university football team were selected to participate in the research. Mechanical properties related to surface-player interaction were assessed on the two surfaces selected for this study. A randomized design was used and the players performed the Ball-sport Endurance and Sprint Test (BEAST90) on the different artificial turf fields. Average time of the 20 m sprints was longer on the FIFA Quality Pro surface than on the non-certified pitch (+ 0.13 s; p < 0.05; CI 95% - 0.01 to 0.27; ES: 0.305). The players' perceived effort was higher in the first (+ 2.64; p < 0.05; CI 95% 0.92 to 4.35; ES: 1.421) and the second half (+ 1.35; p < 0.05; CI 95% - 0.02 to 2.72; ES: 0.637) of the test on the FIFA Quality Pro field. Comparative analysis between surfaces showed no significant differences in the time spent in each of the heart rate zones and higher concentrations of CK (+ 196.58; p > 0.05; CI 95% 66.54 to 326.61; ES: 1.645) were evidenced in the non-certified pitch surface. In response to a simulated match protocol, markers of post-exercise muscle damage may be reduced on accredited artificial turf fields. These insights can provide the opportunity to maximize the efficiency of training sessions and reduce the risk of injury during the season.



#3 Safety and Effects of Football in Skeletal Metastatic Prostate Cancer: a Subgroup Analysis of the FC Prostate Community Randomised Controlled Trial

Reference: Sports Med Open. 2021 Apr 20;7(1):27.  doi: 10.1186/s40798-021-00318-6.

Authors: Eik Dybboe Bjerre, Sarah Weller, Mads Hvid Poulsen, Søren Sørensen Madsen, Rie Dybboe Bjerre, Peter Busch Østergren, Michael Borre, Klaus Brasso, Julie Midtgaard

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Summary: Skeletal metastatic disease excludes many cancer patients from participating in exercise and physical activity due to safety concerns. Empirical evidence from high-quality trials is warranted to guide clinicians and patients.The aim was to evaluate the safety and potential benefits of high-impact aerobic exercise in patients with prostate cancer with skeletal metastases. Exploratory subgroup analysis of a pragmatic, multicentre, parallel randomised controlled trial. The trial recruited 214 patients from five hospital urological departments in Denmark. Patients with prostate cancer with skeletal metastases (n = 41). Six months of football training twice weekly at a local club or usual care. Both groups received brief information on physical activity recommendations at the time of randomisation. Safety, defined as falls, fractures and hospital admissions were used as outcome measures. Effects were evaluated on the primary outcome (prostate cancer-specific quality of life) and secondary outcomes (lean body mass, fat mass, hip and spine bone mineral density, and general physical and mental health). The original trial comprised 214 participants, 41 of whom had skeletal metastases at enrolment. Of these, 22 were allocated to football and 19 to usual care. The trial retention rate was 95% at 12 weeks and 88% at 6 months. Football participants attended 13 sessions on average at 12 weeks and 23 at 6 months. There were two falls, one in each group after 6 months, and no fractures. There were four unplanned hospital admissions in the study period, all four in the usual care group. Statistically significant between-group difference was observed in the primary outcome change in prostate cancer-specific quality of life at 12 weeks (7.6 points [95% CI 0.5 to 15.0]; P = 0.038). No statistical changes were found in the secondary outcomes. The analysis showed that football training was safe in patients with skeletal metastatic prostate cancer and significantly improved quality of life. Larger analyses and/or trials are warranted to confirm the safety of exercise more broadly in cancer patients with skeletal metastatic disease.



#4 Physical Activity Levels of Adult Virtual Football Players

Reference: Front Psychol. 2021 Mar 26;12:596434.  doi: 10.3389/fpsyg.2021.596434. eCollection 2021.

Authors: Ana M Pereira, Evert Verhagen, Pedro Figueiredo, André Seabra, António Martins, João Brito

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Summary: Esports, including virtual football, are a worldwide phenomenon. Yet, little is known about the physical activity levels of individuals engaged in virtual football game play. Therefore, we aimed to perform a preliminary evaluation of the levels of physical activity, sedentarism, and habits of physical training of adults engaged with virtual football in Portugal. This was a cross-sectional investigation based on a structured online survey using the International Physical Activity Questionnaire (IPAQ) and a set of questions regarding habits of physical training. The participants (n = 433) reported spending a median of 5,625 MET-min⋅week-1 being physically active. Still, the participants spent 320 min/day sitting, and 150 min/day practicing virtual football. According to the IPAQ scores, high physical activity levels were reported by 84.5% of the participants, and 87.1% were considered physically active considering the WHO guidelines on physical activity and sedentary behavior. Overall, 60.0% of the participants reported planning their own physical training. Maintaining or improving overall physical health was one of the main reasons for doing physical training (66.7%), with only 6.1% responding being active to improve virtual football performance. Overall, the results showed that virtual football players accomplished the standard recommendations for physical activity, with high levels of physical activity, and encompassing regular physical training focused mostly on health promotion, rather than improved virtual football performance.



#5 Staying on the ball during COVID-19 pandemic: impact on training modalities in football players

Reference: J Sports Med Phys Fitness. 2021 Apr 19.  doi: 10.23736/S0022-4707.21.12256-X. Online ahead of print.

Authors: Dominik Schüttler, Wolfgang Hamm, Simone Krammer, Julius Steffen, Eileen Deuster, Michael Lauseker, Florian Egger, Tim Meyer, Stefan Brunner

Summary: COVID-19 pandemic has affected worldwide sports competitions and training in both amateur and professional leagues. We thus aimed to investigate changes in different training modalities in elite and amateur football players following COVID-19 lockdown in March 2020. In this cross-sectional study we applied a Likert scale-based questionnaire with 20 items to quantify and classify time spent at standard training methods in 47 professional and 54 amateur football players from 12 Austrian clubs before and during lockdown.  Additionally, McLean score was calculated to assess perceived training fatigue. Weekly amount of training time at endurance exercises (cycling) increased in both professional (37.5 [IQR 46.5] min/week vs. 187.5 [IQR 127.5] min/week, p<0.001), and amateur players (0.0 [IQR 45.0] min/week vs. 37.5 [IQR 112.5] min/week, p=0.015) during COVID-19 lockdown. Time on diverse muscle strengthening workouts was significantly elevated in both cohorts. Total training time at ball declined for professionals (from 472.5 [IQR 150] min/week to 15.0 [IQR 112.5] min/week, p<0.001) and amateurs (from 337.5 [IQR 285] min/week to 0.0 [IQR 37.5] min/week, p<0.001). Videoguided training was intensified in both groups (p<0.001 each). Location shifted from football fields and gyms to home and outdoors. Overall McLean score remained unchanged in amateurs (p=0.42) while elite players showed a trend towards an increase (p=0.056). COVID-19 lockdown compromised football training, especially training concepts with ball. Consequently, resulting changes in exercise loads and muscular burden might impact susceptibility for injuries and impair performances especially in amateur players, especially as they lacked training supervision and professional training plans. Minimum effective dose of training workload in order to maintain endurance- and neuromuscular-related performance parameters should be prescribed.



#6 Modulators of Change-of-Direction Economy After Repeated Sprints in Elite Soccer Players

Reference: Int J Sports Physiol Perform. 2021 Apr 19;1-7.  doi: 10.1123/ijspp.2020-0740. Online ahead of print.

Authors: Filippo Dolci, Andrew E Kilding, Tania Spiteri, Paola Chivers, Ben Piggott, Andrew Maiorana, Nicolas H Hart

Summary: The purpose was to investigate the acute effect of repeated-sprint activity (RSA) on change-of-direction economy (assessed using shuttle running economy [SRE]) in soccer players and explore neuromuscular and cardiorespiratory characteristics that may modulate this effect. Eleven young elite male soccer players (18.5 [1.4] y old) were tested on 2 different days during a 2-week period in their preseason. On day 1, lower-body stiffness, power and force were assessed via countermovement jumps, followed by an incremental treadmill test to exhaustion to measure maximal aerobic capacity. On day 2, 2 SRE tests were performed before and after a repeated-sprint protocol with heart rate, minute ventilation, and blood lactate measured. Pooled group analysis indicated no significant changes for SRE following RSA due to variability in individual responses, with a potentiation or impairment effect of up to 4.5% evident across soccer players. The SRE responses to RSA were significantly and largely correlated to players' lower-body stiffness (r = .670; P = .024), and moderately (but not significantly) correlated to players' force production (r = -.455; P = .237) and blood lactate after RSA (r = .327; P = .326). In summary, SRE response to RSA in elite male soccer players appears to be highly individual. Higher lower-body stiffness appears as a relevant physical contributor to preserve or improve SRE following RSA.



#7 Male collegiate soccer athletes with severe ankle laxity display increased knee abduction during side-cutting tasks compared to those with only perceived ankle instability

Reference: Res Sports Med. 2021 Apr 20;1-10.  doi: 10.1080/15438627.2021.1917407. Online ahead of print.

Authors: Shun Kunugi, Takashi Koumura, Ryota Myotsuzono, Akihiko Masunari, Naruto Yoshida, Shumpei Miyakawa, Naoki Mukai

Summary: This study aimed to examine lower limb kinematics during a side-cutting task in male collegiate soccer athletes with severe ankle laxity. Forty-seven participants with a history of ankle sprains and perceived ankle instability were categorized into non-laxity (n = 17), laxity (n = 19), and severe laxity (n = 11) groups using stress radiography tests. Three-dimensional kinematic data during the stance phase of a 45° side-cutting task were analysed. The frontal plane kinematics of the knee significantly differed between the three groups (p < 0.05). The severe laxity group exhibited a greater abduction angle than the non-laxity group (p < 0.05). The horizontal and sagittal plane kinematics of the rearfoot differed between the three groups during the end of the stance phase (p < 0.05). Our data suggest that collegiate soccer athletes with both perceived ankle instability and severe ankle laxity exhibit greater knee abduction movement during a 45° side-cutting task compared to those with only perceived ankle instability.



#8 Hamstring and Quadriceps Muscle Strength in Youth to Senior Elite Soccer: A Cross-Sectional Study Including 125 Players

Reference: Int J Sports Physiol Perform. 2021 Apr 22;1-7.  doi: 10.1123/ijspp.2020-0713. Online ahead of print.

Authors: Lasse Ishøi, Kasper Krommes, Mathias F Nielsen, Kasper B Thornton, Per Hölmich, Per Aagaard, Juan J J Penalver, Kristian Thorborg

Summary: Increasing age, high quadriceps strength, and low hamstring muscle strength are associated with hamstring strain injury in soccer. The authors investigated the age-related variation in maximal hamstring and quadriceps strength in male elite soccer players from under-13 (U-13) to the senior level. A total of 125 elite soccer players were included from a Danish professional soccer club and associated youth academy (first tier; U-13, n = 19; U-14, n = 16; U-15, n = 19; U-17, n = 24; U-19, n = 17; and senior, n = 30). Maximal voluntary isometric force was assessed for the hamstrings at 15° knee joint angle and for the quadriceps at 60° knee joint angle (0° = full extension) using an external-fixated handheld dynamometer. Hamstring-to-quadriceps strength (H:Q) ratio and hamstring and quadriceps maximal voluntary isometric force levels were compared across age groups (U-13 to senior). Senior players showed 18% to 26% lower H:Q ratio compared with all younger age groups (P ≤ .026). Specific H:Q ratios (mean [95% confidence interval]) were as follows: senior, 0.45 (0.42-0.48); U-19, 0.61 (0.55-0.66); U-17, 0.56 (0.51-0.60); U-15, 0.59 (0.54-0.64); U-14, 0.54 (0.50-0.59); and U-13, 0.57 (0.51-0.62). Hamstring strength increased from U-13 to U-19 with a significant drop from U-19 to the senior level (P = .048), whereas quadriceps strength increased gradually from U-13 to senior level. Elite senior soccer players demonstrate lower H:Q ratio compared with youth players, which is driven by lower hamstring strength at the senior level compared with the U-19 level combined with a higher quadriceps strength. This discrepancy in hamstring and quadriceps strength capacity may place senior-level players at increased risk of hamstring muscle strain injuries.



#9 A case of an injured calcaneus secundarius in a professional soccer player

Reference: BMC Musculoskelet Disord. 2021 Apr 22;22(1):374.  doi: 10.1186/s12891-021-04246-0.

Authors: Kepka Sabrina, Morel Marc, Garnier Franck, Pietra François, Marjanovic Nicolas, Zeller Pascal, Bilbault Pascal, Kremer Stéphane, Bierry Guillaume 

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Summary: The calcaneus secundarius (CS) is an accessory ossicle of the anterior facet of the calcaneus and is usually asymptomatic. This accessory bone can be frequently mistaken for a fracture of the anterior process of the calcaneus. Few reports of symptomatic CS have been published, and physicians need to be familiar with imaging strategies when encountering chronic ankle pain or in case of suspicion of fracture of the anterior process of the calcaneus. We describe the case of symptomatic CS in a professional soccer player injured during a match. First, computed tomography showed a large CS. Second, magnetic resonance imaging (MRI) demonstrated synchondrosis between the CS and the calcaneus, as well as edema (high MR T2 signal) within it, corresponding to posttraumatic edema. The patient was successfully treated with nonsteroidal anti-inflammatory drugs and physiotherapy; no surgical management was necessary. At the 4-week follow-up, he was pain-free and returned to activity. This case illustrates the role of imaging for the diagnosis of CS in cases of acute pain of the foot. CT, as well as MRI, helped to confirm the diagnosis of CS traumatized synchondrosis, which can be mistaken for a fracture.



#10 Effects of sprint distance and repetition number on energy system contributions in soccer players

Reference: J Exerc Sci Fit. 2021 Jul;19(3):182-188.  doi: 10.1016/j.jesf.2021.03.003. Epub 2021 Apr 1.

Authors: Süleyman Ulupınar, Serhat Özbay, Cebrail Gençoğlu, Emerson Franchini, Necip Fazıl Kishalı, İzzet İnce

Summary: This study aims to compare the effect of sprint distance and repetition number on performance, physiological responses, and energy systems contributions. Eighteen male university league soccer players (age: 19.9 ± 1.6 years, height: 177.9 ± 4.7 cm, body mass: 72.4 ± 6.3 kg, percentage body fat: 8.9 ± 1.8, training experience: 7.4 ± 1.6 years) completed two different repeated sprint protocols: 20 × 20 m (20 × 20) and 10 × 40 m (10 × 40) with 15s and 30s rest intervals, respectively. Oxygen uptake (VO2) were measured during the rest, exercise, and recovery phases. Rest and peak blood lactate concentrations were determined. Using VO2 and lactate values, the energy system contributions were calculated using a mono-exponential model and mathematical calculations. Energy systems contributions and total energy expenditure (TEE) were calculated both for the entire protocol (overall) and for the sprints only. Ratings of perceived exertion (RPE), peak and mean heart rate (HR) responses were significantly higher in the 20 × 20 whereas lactate response was higher in the 10 × 40. TEE was similar between the 10 × 40 (586.3 ± 60.8 kJ) and 20 × 20 (595.6 ± 57.5 kJ). For overall estimations, the 10 × 40 and 20 × 20 presented similar results of oxidative (47.5 ± 5.4 vs 45.7 ± 5.1 kJ min-1) and phosphagen (44.7 ± 5.4 vs (42.9 ± 4.8 kJ min-1) systems contributions whereas glycolytic contribution was higher in the 10 × 40 (15.5 ± 2.2 vs 12.8 ± 2.3 kJ min-1). For sprints only estimation, the phosphagen (257.6 ± 31.5 vs 225.2 ± 28.2 kJ min-1), glycolytic (89.4 ± 13.4 vs 67.3 ± 12.5 kJ min-1), and oxidative (76.9 ± 6.9 vs 72.0 ± 7.9 2 kJ min-1) systems contributions were higher in the 10 × 40. Although HR and RPE responses were higher in the 20 × 20, phosphagen (during sprints) and glycolytic (during both sprints and overall protocol) were higher in the 10 × 40 protocol. Therefore, the 10 × 40 protocol seems more reasonable for developing or evaluating the anaerobic systems.



#11 A Goal Scoring Probability Model for Shots Based on Synchronized Positional and Event Data in Football (Soccer)

Reference: Front Sports Act Living. 2021 Mar 29;3:624475.  doi: 10.3389/fspor.2021.624475. eCollection 2021.

Authors: Gabriel Anzer, Pascal Bauer

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Summary: Due to the low scoring nature of football (soccer), shots are often used as a proxy to evaluate team and player performances. However, not all shots are created equally and their quality differs significantly depending on the situation. The aim of this study is to objectively quantify the quality of any given shot by introducing a so-called expected goals (xG) model. This model is validated statistically and with professional match analysts. The best performing model uses an extreme gradient boosting algorithm and is based on hand-crafted features from synchronized positional and event data of 105, 627 shots in the German Bundesliga. With a ranked probability score (RPS) of 0.197, it is more accurate than any previously published expected goals model. This approach allows us to assess team and player performances far more accurately than is possible with traditional metrics by focusing on process rather than results.



#12 Internal, external and repeated-sprint demands in small-sided games: A comparison between bouts and age groups in elite youth soccer players

Reference: PLoS One. 2021 Apr 28;16(4):e0249906.  doi: 10.1371/journal.pone.0249906. eCollection 2021.

Authors: Richard Hauer, Paul Störchle, Bettina Karsten, Harald Tschan, Arnold Baca

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Summary: This study investigated the activity profile during small-sided games (SSG) in elite youth soccer players. Internal load (IL) including heart rate (HR) and external load (EL) such as distance covered in different speed-zones (SZ) were collected from forty-eight players of three different teams (U15, U16, U18). The investigation included a total of eighteen 5vs.5 SSGs, each consisting of four 2-minute bouts on a 40x32m pitch during spring season. Total group results (n = 48) showed a reduction in total-distance (p = 0.001; [Formula: see text] = 0.12), high-intensity-running (p = 0.009; [Formula: see text] = 0.09), and low-intensity-running distance (p = 0.028; [Formula: see text] = 0.07) between bouts. Similarly, a reduction in the number of both acceleration-low (p = 0.001; [Formula: see text] = 0.12) and deceleration-high (p = 0.003; [Formula: see text] = 0.11) values was observed. Additionally, time spent in HR-zones 3 and 4 (p≤0.007; [Formula: see text] ≥ 0.10), increased, with a reduction in HR-zone 1 (p = 0.000, [Formula: see text] = 0.25). Age group comparison showed less distance covered in SZ 1 (p≤0.000; [Formula: see text] = 0.56) and greater deceleration-high values (p≤0.038; [Formula: see text] = 0.32) in U15 players compared to other age groups. Further, U15 showed lower values in low-intensity-running compared to U18 (p = 0.038; [Formula: see text] = 0.22). No age-related differences were found for IL and repeated sprint ability (RSA) values. The higher EL in younger age groups should be taken into account when implementing soccer specific SSGs. In addition, HRmean values between 80-85% of HRmax and RSA numbers, which are similar to match-play data, indicate SSGs as an effective training tool to prepare youth soccer athletes for the demands of competition.



#13 Experience of cold-water immersion on recovery efficiency after soccer match

Reference: Tunis Med. 2021 Feb;99(2):252-258.

Authors: Mostafa Farkhari Babak, Mohammad Mosaferi Ziaaldini, Attarzadeh Hoseini Seyyed Reza

Summary: immersion in cold-water is one of the most common recovery and rehabilitation techniques among athletes. However, several factors such as shocking induced by cold water can affect the effectiveness of this technique. The aim of this study was to investigate the effect of 4 weeks cold water habituation on the effectiveness of CWI recovery technique on muscle damage and function indices of young soccer players. Twenty young men with no previous experience of CWI participated in this study. Output power and RSADec of subjects were measured. The subjects then performed a simulated soccer test and, after collecting blood samples, were immediately immersed in 15 ° C water for 15 minutes. Twenty-four hours later blood sampling and functional tests were repeated. Subjects then were divided randomly into two groups of exercise with CWI recovery and exercise with passive recovery. After four weeks, the blood sampling and performance tests repeated like the pre-test.

Results: The CWI had no significant effect on serum levels of AST and LDH before and after 4 weeks of CWI (P> 0.05). Also, there was no significant difference in power output and RSADec after CWI before and after cold water habituation (P> 0.05). It seems that the experience of recovering by immersion in cold-water has no effect on the effectiveness of this method. Therefore, soccer coaches and athletes should think more about using this recovery method.



#14 Intra- and Inter-week Variations of Well-Being Across a Season: A Cohort Study in Elite Youth Male Soccer Players

Reference: Front Psychol. 2021 Apr 9;12:671072.  doi: 10.3389/fpsyg.2021.671072. eCollection 2021.

Authors: Hadi Nobari, Maryam Fani, Filipe Manuel Clemente, Jorge Carlos-Vivas, Jorge Pérez-Gómez, Luca Paolo Ardigò

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Summary: This study describes the weekly variations of well-being ratings relative to fatigue (wFatigue), stress (wStress), delayed-onset muscle soreness (wDOMS), sleep quality (wSleep), and Hooper questionnaire (wHQ) throughout the season. In addition, the well-being variables for the playing position in different moments of the season were discussed. Twenty-one elite young soccer players U17 took part in this study. From the beginning of the pre-season, well-being status was monitored daily by the HQ method throughout 36 weeks, including four periods: (1) pre-season, (2) early-season, (3) mid-season, and (4) end-season. Players trained at least 3 times per week throughout the season. The main outcome was that, in weeks 33 and 28, the highest [wFatigue: 15.85 ± 3.38 arbitrary units (AU); wHQ: 48.86 ± 9.23 AU] and the lowest (wFatigue: 5.38 ± 1.88 AU; wHQ: 20.43 ± 5.49 AU) wFatigue and wHQ occurred, respectively, although the lowest level of wDOMS happened in week 28 (4.86 ± 2.15 AU), while the highest wDOMS was observed in week 5 (14.65 ± 4.16 AU). The highest wSleep (13.00 ± 2.12 AU) and wStress (11.65 ± 2.92 AU) were observed in weeks 8 and 34, respectively, while the lowest wSleep (5.81 ± 2.29 AU) and wStress (3.76 ± 0.94 AU) were marked in week 29 coincidentally. In the HQ between every weekday, except recovery day, and the day of the match (MD), considerable highest HQ was only revealed in 2 days after MD in contrast to overall team comparison. In the present study, we observed that the well-being changes between different phases of the season as well as between weeks and days of the week with the MD are significant. These results provide a great point of view for coaches and practitioners about well-being variations over a season in elite youth soccer level. As a result, coaches will be more aware about non-functional overreaching and taking measures to prevent it.



#15 From the Laboratory to the Field: IMU-Based Shot and Pass Detection in Football Training and Game Scenarios Using Deep Learning

Reference: Sensors (Basel). 2021 Apr 28;21(9):3071.  doi: 10.3390/s21093071.

Authors: Maike Stoeve, Dominik Schuldhaus, Axel Gamp, Constantin Zwick, Bjoern M Eskofier

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Summary: The applicability of sensor-based human activity recognition in sports has been repeatedly shown for laboratory settings. However, the transferability to real-world scenarios cannot be granted due to limitations on data and evaluation methods. On the example of football shot and pass detection against a null class we explore the influence of those factors for real-world event classification in field sports. For this purpose we compare the performance of an established Support Vector Machine (SVM) for laboratory settings from literature to the performance in three evaluation scenarios gradually evolving from laboratory settings to real-world scenarios. In addition, three different types of neural networks, namely a convolutional neural net (CNN), a long short term memory net (LSTM) and a convolutional LSTM (convLSTM) are compared. Results indicate that the SVM is not able to reliably solve the investigated three-class problem. In contrast, all deep learning models reach high classification scores showing the general feasibility of event detection in real-world sports scenarios using deep learning. The maximum performance with a weighted f1-score of 0.93 was reported by the CNN. The study provides valuable insights for sports assessment under practically relevant conditions. In particular, it shows that (1) the discriminative power of established features needs to be reevaluated when real-world conditions are assessed, (2) the selection of an appropriate dataset and evaluation method are both required to evaluate real-world applicability and (3) deep learning-based methods yield promising results for real-world HAR in sports despite high variations in the execution of activities.



#16 Differences in Maturity and Anthropometric and Morphological Characteristics among Young Male Basketball and Soccer Players and Non-Players

Reference: Int J Environ Res Public Health. 2021 Apr 8;18(8):3902. doi: 10.3390/ijerph18083902.

Authors: Stefania Toselli, Francesco Campa, Pasqualino Maietta Latessa, Gianpiero Greco, Alberto Loi, Alessia Grigoletto, Luciana Zaccagni 

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Summary: An aspect that influences sport performance is maturation status, since, within the same chronological age group, boys who have advanced maturation outperform their late maturing peers in tests of muscular strength, power, and endurance. Therefore, the aims of the present study were: (i) to investigate the differences in biological maturation and anthropometric and morphological characteristics among three groups of Italian adolescents, two of which were sportive (practicing basketball and football) and one non-sportive, and (ii) to identify the anthropometric and morphological predictors that best discriminate these three groups. Methods: Sixty-one basketball and 62 soccer players and 68 non-sportive youths were measured (mean age = 13.0 ± 1.1 y). Anthropometric characteristics were taken and body mass index, cormic index, body composition parameters, and somatotype were derived. An estimation of maturity status was carried out considering the years from peak height velocity (PHV). Two-way 3 × 3 ANOVAs was performed on all anthropometric characteristics to test the differences within sport groups and maturity status groups. Discriminant function analysis (stepwise criteria) was then applied to anthropometric and body composition variables to classify subjects into the three different sport categories. Results: Differences in anthropometric characteristics were detected among the three groups. For somatotype, differences among all of the considered groups were higher for endomorphy (p < 0.001; effect size = 0.13). Biological maturity influences the differences in the anthropometric characteristics and body composition among subjects of the same chronological age during adolescence. The variables that best discriminated the three groups were represented by body composition parameters, body proportions, and body build. Conclusions: This study confirms that boys who practice sport present healthier body composition parameters, with lower level of fat parameters. The assessment of maturity status is a fundamental factor in explaining anthropometric and body composition differences among peers in this period. Its comprehension may assist coaches and technical staff in optimizing competitive efficiency and monitoring the success of training regimes.






The Relationship Between Performance and Asymmetries in Different Multidirectional Sprint Tests in Soccer Players

The aims of this study were to analyze the association between linear sprint, curved sprints (CS) and change-of-direction (COD) speed performances and compare the association and direction of asymmetries between skills.





High-Intensity Intermittent Exercise Performed on the Sand Induces Higher Internal Load Demands in Soccer Players

This study aimed to examine the acute physiological effect of shuttle-run-based high-intensity intermittent exercise (HIIE) performed at the same relative speed (i.e. 100%PST−CAR) on sand (SAND) and grass (GRASS) in male junior soccer players.





Latest research in football - week 28 - 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 A Preseason Training Program With the Nordic Hamstring Exercise Increases Eccentric Knee Flexor Strength and Fascicle Length in Professional Female Soccer Players

Reference: Int J Sports Phys Ther. 2021 Apr 1;16(2):459-467.  doi: 10.26603/001c.19452.

Authors: Karoline Baptista Vianna, Lívia Gonçalves Rodrigues, Nathalia Trevisol Oliveira, João Breno Ribeiro-Alvares, Bruno Manfredini Baroni

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Summary: Training programs that include the Nordic hamstring exercise (NHE) have been shown to increase eccentric knee flexor strength and biceps femoris fascicle length in male athletes. However, the effect of NHE on female athletes remains unknown. The aim was to investigate the collective and individual responses of professional female soccer players engaged in a preseason training program with the NHE regarding eccentric knee flexor strength and biceps femoris long head fascicle length. Sixteen amateur female soccer players (without a NHE training routine) were evaluated 8-weeks apart to: (1) assess reliability of eccentric knee flexor strength and biceps femoris fascicle length measures; and (2) determine the typical error of measures that would be used to discriminate training responders and non-responders. The NHE training group had 17 professional female soccer players who performed an 8-week training program with the NHE during preseason. Within-group analysis was performed with paired sample t-tests (pre- vs. post-training), and individual responses were determined using the typical error criteria. The non-trained group's data demonstrated that measures of strength (ICC=0.82-0.87, typical error = 12-13 N) and fascicle length (ICC=0.92-0.97; typical error = 0.19-0.38 cm) were reliable. In the NHE training group, both limbs increased the eccentric knee flexor strength (~13%; ES=0.74-0.82) and the biceps femoris fascicle length (~6%; ES=0.44-0.65). Twelve players (~71%) were considered responders to the NHE training program for the eccentric knee flexor strength, while eight athletes (~47%) were responders for the biceps femoris fascicle length. The 8-week preseason training program with the NHE increased both eccentric knee flexor strength and biceps femoris fascicle length in professional female soccer players. More than two-thirds of players demonstrated a meaningful increase in eccentric strength, while nearly half achieved consistent fascicle length increases with the NHE training.



#2 Screening to Detect Hip and Groin Problems in Elite Adolescent Football (Soccer) Players - Friend or Foe?

Reference: Int J Sports Phys Ther. 2021 Apr 2;16(2):591-593.  doi: 10.26603/001c.21525.

Authors: Matthew D DeLang, J Craig Garrison, Kristian Thorborg

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Summary: Injury prevention strategies in team settings should not overlook early detection and secondary prevention. Monitoring systems may be an effective approach to detect common and troublesome injuries, such as hip and groin pain in football (soccer) players. The purpose of this International Perspective is to share our experiences with monitoring hip and groin pain in youth academy football and discuss challenges that surfaced. We consider why players may not accurately report pain, their perceptions of groin pain, and whether all groin pain is clinically meaningful.



#3 How Soccer Scouts Identify Talented Players

Reference: Eur J Sport Sci. 2021 Apr 16;1-39.  doi: 10.1080/17461391.2021.1916081. Online ahead of print.

Authors: Tom L G Bergkamp, Wouter G P Frencken, A Susan M Niessen, Rob R Meijer, Ruud J R den Hartigh

Summary: Scouts of soccer clubs are often the first to identify talented players. However, there is a lack of research on how these scouts assess and predict overall soccer performance. Therefore, we conducted a large-scaled study to examine the process of talent identification among 125 soccer scouts. Through an online self-report questionnaire, scouts were asked about 1) the players' age at which they can predict players' soccer performance, 2) the attributes they consider relevant, and 3) the extent to which they predict performance in a structured manner. The most important results are as follows. First, scouts who observed 12-year-old and younger players perceived they could predict at older ages (13.6 years old, on average) whether a player has the potential to become a professional soccer player. This suggests that scouts are aware of the idea that early indicators of later performance are often lacking, yet do advise on selection of players at younger ages. Second, when identifying talented players, scouts considered more easily observable attributes, such as technical attributes. However, scouts described these often in a broad sense rather than in terms of specific predictors of future performance. Finally, scouts reported that they assess attributes of players in a structured manner. Yet, they ultimately based their prediction (i.e., final score) on an intuitive integration of different performance attributes, which is a suboptimal strategy according to existing literature. Taken together, these outcomes provide specific clues to improve the reliability and validity of the scouting process.



#4 Biceps Femoris Compensates for Semitendinosus After Anterior Cruciate Ligament Reconstruction With a Hamstring Autograft: A Muscle Functional Magnetic Resonance Imaging Study in Male Soccer Players

Reference: Am J Sports Med. 2021 Apr 16;3635465211003309.  doi: 10.1177/03635465211003309. 

Authors: Thomas Tampere, Jan Victor, Thomas Luyckx, Hannes Vermue, Nele Arnout, Erik Witvrouw, Joke Schuermans

Summary: Rates of reinjury, return to play (RTP) at the preinjury level, and hamstring strain injuries in male soccer players after anterior cruciate ligament reconstruction (ACLR) remain unsatisfactory, due to multifactorial causes. Recent insights on intramuscular hamstring coordination revealed the semitendinosus (ST) to be of crucial importance for hamstring functioning, especially during heavy eccentric hamstring loading. Scientific evidence on the consequences of ST tendon harvest for ACLR is scarce and inconsistent. This study intended to investigate the repercussions of ST harvest for ACLR on hamstring muscle function. The hypothesis is that harvesting of the ST tendon for ACLR was expected to have a significant influence on hamstring muscle activation patterns during eccentric exercises, evaluated at RTP in a population of male soccer athletes. A total of 30 male soccer players with a history of ACLR who were cleared for RTP and 30 healthy controls were allocated to this study during the 2018-2019 soccer season. The influence of ACLR on hamstring muscle activation patterns was assessed by comparing the change in T2 relaxation times [ΔT2 (%) = post−exercise−T2pre−exerciseT2pre−exercisepost-exercise-T2pre-exerciseT2pre-exercise] of the hamstring muscle tissue before and after an eccentric hamstring loading task between athletes with and without a recent history of ACLR through use of muscle functional magnetic resonance imaging, induced by an eccentric hamstring loading task between scans. Significantly higher exercise-related activity was observed in the biceps femoris (BF) of athletes after ACLR compared with uninjured control athletes (13.92% vs 8.48%; P = .003), whereas the ST had significantly lower activity (19.97% vs 25.32%; P = .049). Significant differences were also established in a within-group comparison of the operated versus the contralateral leg in the ACLR group (operated vs nonoperated leg: 14.54% vs 11.63% for BF [P = .000], 17.31% vs 22.37% for ST [P = .000], and 15.64% vs 13.54% for semimembranosus [SM] [P = .014]). Neither the muscle activity of SM and gracilis muscles nor total posterior thigh muscle activity (sum of exercise-related ΔT2 of the BF, ST, and SM muscles) presented any differences in individuals who had undergone ACLR with an ST tendon autograft compared with healthy controls. These findings indicate that ACLR with a ST tendon autograft might notably influence the function of the hamstring muscles and, in particular, their hierarchic dimensions under fatiguing loading circumstances, with increases in relative BF activity contribution and decreases in relative ST activity after ACLR. This between-group difference in hamstring muscle activation pattern suggests that the BF partly compensates for deficient ST function in eccentric loading. These alterations might have implications for athletic performance and injury risk and should probably be considered in rehabilitation and hamstring injury prevention after ACLR with a ST tendon autograft.



#5 Evaluation of stoppage time due to field injuries in professional football games: do players really need medical help so often?

Reference: Res Sports Med. 2021 Apr 16;1-10.  doi: 10.1080/15438627.2021.1917409. Online ahead of print.

Authors: Gürhan Dönmez, Şerife Şeyma Torgutalp, Ömer Özkan, Ömer Faruk İlicepınar, Feza Korkusuz, Savaş Kudaş

Summary: This study aimed to identify the incidence of stoppage time due to field injuries in professional football (soccer) games and to evaluate if the players involved really need medical care and whether team physicians deal with fake injuries. A total of 893 injury time-outs occurred leading to 956 treatments during 266 matches included in the study. The mean stoppage time was 88.7 ± 34.4 seconds. Less than one fifth of the injuries (17.4%) resulted in an impossibility to complete the game. The overall time-loss injury incidence which led players to miss the next game was 9.1/1000 match-hours (n = 80, 8.4% of all injuries). The players on teams in the lead at the time of the incident had significantly higher injury time-out incidence than players on teams who were losing (p < 0.05). Increasing the knowledge of team physicians, coaches, referees, and rule-makers about the medical needs of players during the game will help to identify the behaviour pattern of players.



#6 Acceleration and High-Speed Running Profiles of Women's International and Domestic Football Matches

Reference: Front Sports Act Living. 2021 Mar 25;3:604605.  doi: 10.3389/fspor.2021.604605. eCollection 2021.

Authors: Jesse Griffin, Timothy Newans, Sean Horan, Justin Keogh, Melissa Andreatta, Clare Minahan

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Summary: Acceleration and deceleration are important given football is an intermittent sport with constant changes in velocity and direction. It is unclear, however, if the accelerations and decelerations performed by players differ between competition levels. The aim of the present study was to compare the acceleration, deceleration, and high-speed running profiles of players during international and domestic matches and to determine if differences were apparent across playing positions (defenders, midfielders, and attackers). GPS data from 21 Australian women's domestic football league matches over 2 seasons (2016-2018) and 15 Australian women's international matches (2017-2018) were collected and analyzed. Movement pattern data was collected using VX Sport and GPSports 10 Hz GPS receivers. Variables analyzed included: total distance, distance covered high-speed running (16-20 km·h-1) distance covered sprinting (> 20 km·h-1) and time spent accelerating and decelerating in four predetermined bands (1-2 m·s-2, 2-3 m·s-2, 3-4 m·s-2, and > 4 m·s-2). Results revealed that players competing in international matches covered significantly greater total distances, greater high-speed running distances and greater sprinting distances as well as spending a greater duration accelerating in band 4 compared to players in domestic competitions (p < 0.05). Players competing in international matches spent significantly less duration decelerating in bands 2 and 3, compared to players in domestic competitions. International defenders and midfielders recorded significantly higher total distances and high-speed running distance compared to players in domestic matches. Our findings suggest that preparing players for international-level competition should include progressive exposure to high-speed running and sprinting distances, as well as high magnitude accelerations. Furthermore, the higher running speeds experienced by players during international matches appears to be a result of less time spent decelerating. The optimal deceleration necessary for specific situations appears important and emphasizes the need for specific deceleration training. The increased effort of high-intensity activity that is required for players competing in international matches affects defenders and midfielders to the greatest degree. Gradual exposure to the increased running demands for midfielders and defenders competing in international matches is needed to improve performance and reduce the potential risk of injury.



#7 Does the chronotype distribution vary between different level football leagues? Insights gained from Czech elite football players

Reference: Chronobiol Int. 2021 Apr 11;1-8. doi: 10.1080/07420528.2021.1912075. Online ahead of print.

Authors: Pavol Pivovarnicek, Dominika Kondratova, Efrem Kentiba, Ludmila Jancokova, Tomas Maly

Summary: Chronotype refer to individuals' time-of-day preferences for activities, which can be classified as "morning types = (M-types)", "evening types = (E-types)", and "neither types (N-types)". The primary aim of this study was to compare the chronotype distribution of Czech First League (1L) and Czech National Football League (2L) male elite football players, which was divided into two secondary aims: (i) statistically identify and compare the number (presence) of particular chronotypes in 1L, and (ii) statistically identify and compare the number (presence) of particular chronotypes in 2L. The present cross-sectional study employed a self-reported standardized questionnaire, the Composite Scale of Morningness, to study the chronotype distribution among the male elite football players. The chronotype distribution of 139 (85 from 1L with mean age ± S.D. = 25.5 ± 3.7 years and 54 from 2L age = 24.4 ± 4.5 years) players was assessed. Overall, 61 (71.8%) of the participants from 1L were mainly N-types, followed by M- and E-types. Similarly, 40 (74.1%) participants from 2L were mainly N-types, followed by M- and E-types. The statistical analysis of the 1L players showed a significantly higher presence of N-types compared to M- and E-types (χ2(2) = 57.62, p < .05, V = .58). The same results were detected in 2L, where the N-type was identified in the majority of football players (χ2(2) = 57.62, p < .05, V = .58). The statistical comparison of the number of presented chronotypes did not show a significant difference (F = 3.29, p > .05, V = .16) between players of the 1L and 2L. Thus, N-types are dominant among Czech elite football players, and the chronotype distribution of male elite football players from the Czech First League and the Czech National Football League does not vary.



#8 Drill design using the 'control-chaos continuum': Blending science and art during return to sport following knee injury in elite football

Reference: Phys Ther Sport. 2021 Feb 24;50:22-35.  doi: 10.1016/j.ptsp.2021.02.011. Online ahead of print.

Authors: T Allen, S Wilson, D D Cohen, M Taberner

Summary: Establishing the level of risk, planning and adapting the return to sport (RTS) process following a complex knee injury involves drawing on a combination of relevant high-quality evidence and practitioner experience. On-pitch rehabilitation is a critical element of this process, providing an effective transition from rehabilitation to team training. The 'control-chaos continuum' (CCC) is an adaptable framework for on-pitch rehabilitation moving from high control to high chaos, progressively increasing running load demands and incorporating greater perceptual and neurocognitive challenges within sport-specific drills. Drills are a key element of the CCC, and are designed to ensure specificity, ecological validity and maintaining player interest. We showcase drill progression through the phases of the CCC, highlighting the use of constraints to create drills that incorporate the physical, technical, tactical and injury-specific needs of the player. We also provide recommendations to help practitioners create training session content using the CCC to help replicate the demands of team training within their own environment.



#9 Analysis of the worst-case scenarios in an elite football team: Towards a better understanding and application

Reference: J Sports Sci. 2021 Apr 10;1-10.  doi: 10.1080/02640414.2021.1902138. Online ahead of print.

Authors: Andrew R Novak, Franco M Impellizzeri, Arjav Trivedi, Aaron J Coutts, Alan McCall

Summary: This study investigated the variability in the worst-case scenario (WCS) and suggested a framework to improve the definition and guide further investigation. Optical tracking data from 26 male players across 38 matches were analysed to determine the WCS for total distance, high-speed running (>5.5 m.s-1) and sprinting (>7.0 m.s-1) using a 3-minute rolling window. Position, total output, previous epoch, match half, time of occurrence, classification of starter vs substitute, and minutes played were modelled as selected contextual factors hypothesized to have associations with the WCS. Linear mixed effects models were used to account for cross-sectional observations and repeated measures. Unexplained variance remained high (total distance R2 = 0.53, high-speed running R2 = 0.53 and sprinting R2 = 0.40). Intra-individual variability was also high (total distance CV = 4.6-8.2%; high-speed CV = 15.6-37.8% and Sprinting CV = 21.1-76.4%). The WCS defined as the maximal physical load in a given time-window, produces unstable metrics lacking context, with high variability. Furthermore, training drills targetting this metric concurrently across players may not have representative designs and may underprepare athletes for complete match demands and multifaceted WCS scenarios. Using WCS as benchmarks (reproducing similar physical activity for training purposes) is conceptually questionable.



#10 The trunk is exploited for energy transfers of maximal instep soccer kick: A power flow study

Reference: J Biomech. 2021 Apr 9;121:110425.  doi:10.1016/j.jbiomech.2021.110425. Online ahead of print.

Authors: Diego da Silva Carvalho, Juliana Melo Ocarino, Aline de Castro Cruz, Leonardo Drumond Barsante, Breno Gonçalves Teixeira, Renan Alves Resende, Sérgio Teixeira Fonseca, Thales Rezende Souza

Summary: The purpose of this study was to investigate the angular kinetic energy transfers and expenditure among the trunk (bisegmented), the pelvis and the kick limb during maximal soccer instep kicking, and to characterize kicking kinetics and kinematics. Eighteen adult male amateur soccer players (24.0 ± 4.1 years old) were assessed. Three-dimensional kinematics and ground reaction force were measured. A 6-degrees-of-freedom model was assumed, comprising the upper trunk, lower trunk, pelvis, thigh, shank and foot, and the thoraco-lumbar, lumbo-pelvic, hip, knee, and ankle joints. Angular kinematics and joint moments were computed. Power flow analysis was done by calculating the joint powers (to describe joint-to-segments energy transfers) and the proximal and distal segment powers (to describe segment-to-segment transfers). Power, kinematic and kinetic time series were presented to describe the energy flows' directions. The total mechanical energy expenditure (TMEE) at each joint was also calculated. The TMEEs pointed to substantial energy expenditure at the trunk (27% of the summed work produced by the analyzed joints). In the initial phases of kicking, the trunk generates downward energy flows from the upper to the lower trunk and from the lower trunk to the pelvis, and then to the lower limb, sequentially, which favors angular motions for ball contact. There is a formation and release of a tension arc only at the hip joint, and deceleration of the segments slightly sooner than ball contact, differently from theoretical accounts. There are energy flows, hitherto unknown, among the trunk, pelvis and kick limb, revealing mechanical strategies of kicking.



#11 The effects of free weights and iso-inertial resistance during semi-squatting exercise on amateur soccer players' physical performance indicators: a randomized controlled study

Reference: J Sports Med Phys Fitness. 2021 Apr 19.  doi: 10.23736/S0022-4707.21.12281-9. Online ahead of print.

Authors: Andreas Fousekis, Konstantinos Fousekis, Georgios Fousekis, Vasiliki Manou, Yiannis Michailidis, Charalambos Zelenitsas, Thomas Metaxas

Summary: The aim was to compare the effects of two lower extremity strengthening programs using iso-inertial resistance or free weights on amateur soccer players' physical performance indicators. Thirty-five amateur soccer players (average age 22.6±5.1 years) were randomly assigned to iso-inertial group (n=11) or free-weight group (n=11), or control group (n=13). The groups performed two training sessions per week for six weeks. Before and after the strengthening implementation, physical performance indicators were evaluated, including the isokinetic knee extensors and flexors' strength, power, speed, and agility. The significance level was set at p<0.05. The iso-inertial training resistance led to an increase in the hamstrings' eccentric strength at 60°/s and 150°/s (p<0.05) compared to the free-weight resistance (p>0.05) and the controls (p>0.05). No other significant adaptations were observed in the other isokinetic strength, power, speed (10-m, p=0.052) and agility measurements (Illinois agility test, p=0.059). In ratio (knee flexors/knee extensors) the only differences observed was at 150 o/s for iso-inertial group (p<0.05). Iso-inertial resistance training during semi squatting can enhance the hamstrings' eccentric performance andthe soccer players' speed and agility compared to the classic free-weight training program, which should considered when designing strength and injury prevention programs.



#12 Progression from youth to professional soccer: A longitudinal study of successful and unsuccessful academy graduates

Reference: Scand J Med Sci Sports. 2021 Apr;31 Suppl 1:73-84. doi: 10.1111/sms.13701.

Authors: James H Dugdale, Dajo Sanders, Tony Myers, A Mark Williams, Angus M Hunter

Summary: The aim was to optimize use of available resources, professional academies develop strategies to assess, monitor, and evaluate players as they progress through adolescence toward adulthood. However, few published reports exist using longitudinal study designs to examine performance throughout adolescence and the transition from youth to professional soccer. We examined differences in the age of player recruitment alongside longitudinal performance differences on field-based fitness tests of successful vs. unsuccessful graduates across the entire age spectrum recruited by a professional soccer academy. Altogether, 537 youth soccer players volunteered to participate. We recorded the age of recruitment, biannual fitness test performance, and subsequent success in attaining a senior professional contract at the club across a period of 12 years. Only 53 (10%) of players were successful in obtaining a professional contract, with 68% of players who became professional being recruited at 12 years of age or older. Individuals recruited at an earlier age did not display a higher probability of success in attaining a professional contract. Bayesian regression models reported a consistent interaction between age and group for data on all performance measures. Moreover, "successful" academy graduates only physically outperformed their "unsuccessful" counterparts from age ~13-14 years onward, with either no differences in performance, or performance on physical fitness tests favoring "unsuccessful" players prior to this age. Findings suggest that high achievers during childhood and early adolescence may not develop into successful senior professionals, raising concerns about the predictive utility of talent identification models.



#13 Confusion Reigns: An Analysis of Responses to U.S. Soccer Age Cut-Off Date Policy Change

Reference: Front Sports Act Living. 2021 Mar 25;3:635195.  doi: 10.3389/fspor.2021.635195. eCollection 2021.

Authors: Kristy L Smith, Sara Scarfone, Laura Chittle, Sean Horton, Jess C Dixon

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Summary: Relative age effects (RAEs) have been associated with the common practice of grouping athletes by chronological age. Development and selection advantages are often awarded to those who are born closer to, but following, the cut-off date employed by sport systems. In 2015, the U.S. Soccer Federation announced that it would be changing its birth-year registration cut-off date from August 1st to January 1st. This change was introduced to align the U.S. youth soccer calendar with international standards, and simultaneously provide clearer information on player birthdates to "lessen" RAEs. The magnitude of this policy change has led to considerable controversy, with members of the soccer community taking to social media and website blogs, as well as the U.S. Youth Soccer's website, to voice their opinions and general unhappiness with this decision. Thus, the purpose of this study was to provide a summary of online reactions to the policy change, with attention to the manner in which the U.S. Soccer Federation framed (i.e., the underlying rationale for the decision) and publicly communicated its decision to change the annual cut-off date. Qualitative content analysis was used to analyze data collected from 63 social media sites (websites, n = 43; forums, n = 16; blogs, n = 4). From the 3,851 pages of text derived from these sources, a total of 404 unique passages of text were identified within 262 stakeholder posts. Four categories emerged from the data: stakeholder discussion, outcomes identified by stakeholders, recommended courses of action, and communication regarding the policy change. In general, the actions of the U.S. Soccer Federation and related outcomes were negatively perceived by stakeholders at various levels of the sport. Resistance to the change may have been reduced through enhanced communication from the national level and opportunities for stakeholder input. While one objective of this policy change was to combat RAEs, previous research suggests this organizational change will only shift which group of athletes experience relative age (dis)advantages. There appears to be a disconnect between the academic literature and sport policy with respect to solutions for RAEs, which can lead to unintended consequences for various sport stakeholders.



#14 Association of Skeletal Maturity and Injury Risk in Elite Youth Soccer Players: A 4-Season Prospective Study With Survival Analysis

Reference: Orthop J Sports Med. 2021 Mar 31;9(3):2325967121999113.  doi: 10.1177/2325967121999113. eCollection 2021 Mar.

Authors: Olivier Materne, Karim Chamari, Abdulaziz Farooq, Adam Weir, Per Hölmich, Roald Bahr, Matt Greig, Lars R McNaughton

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Summary: The association between injury risk and skeletal maturity in youth soccer has received little attention. The aim was to prospectively investigate injury patterns and incidence in relation to skeletal maturity in elite youth academy soccer players and to determine the injury risks associated with the skeletal maturity status, both overall and to the lower limb apophysis. Descriptive epidemiology study. All injuries that required medical attention and led to time loss were recorded prospectively during 4 consecutive seasons in 283 unique soccer players from U-13 (12 years of age) to U-19 (18 years). The skeletal age (SA) was assessed in 454 player-seasons using the Fels method, and skeletal maturity status (SA minus chronological age) was classified as follows: late, SA >1 year behind chronological age; normal, SA ±1 year of chronological age; early, SA >1 year ahead of chronological age; and mature, SA = 18 years. An adjusted Cox regression model was used to analyze the injury risk.

A total of 1565 injuries were recorded; 60% were time-loss injuries, resulting in 17,772 days lost. Adjusted injury-free survival analysis showed a significantly greater hazard ratio (HR) for different status of skeletal maturity: early vs normal (HR = 1.26 [95% CI, 1.11-1.42]; P < .001) and early vs mature (HR = 1.35 [95% CI, 1.17-1.56]; P < .001). Players who were skeletally mature at the wrist had a substantially decreased risk of lower extremity apophyseal injuries (by 45%-61%) compared with late (P < .05), normal (P < .05), and early (P < .001) maturers. Musculoskeletal injury patterns and injury risks varied depending on the players' skeletal maturity status. Early maturers had the greatest overall adjusted injury risk. Players who were already skeletally mature at the wrist had the lowest risk of lower extremity apophyseal injuries but were still vulnerable for hip and pelvis apophyseal injuries.



#15 Quantitative EEG in sports: performance level estimation of professional female soccer players

Reference: Health Inf Sci Syst. 2021 Mar 26;9(1):14.  doi: 10.1007/s13755-021-00144-w. eCollection 2021 Dec.

Authors: Kittichai Tharawadeepimuk, Yodchanan Wongsawat

Summary: Measuring the peak performance of athletes remains a challenge in movement science and sports psychology. Non-invasive quantitative electroencephalography (QEEG) recordings can be used to analyze various factors in sports psychology. In this context, sports-related psychological factors were used to estimate the performance of Thai professional female soccer players before a competition. The QEEG recordings of thirty-two players were recorded three times: twice before a competition (once a week) and a week after a competition. Four factors of sports psychology were estimated and observed: anxiety, perceptual response to an acute bout of brain activity, assertiveness, and brain central fatigue. A brain topographic map (absolute power) and brain connectivity (coherence and amplitude asymmetry) data were used to analyze sports-related psychological factors. These factors were measurable based on the brain activity of the athletes and could be used to evaluate their performance during competitions by using QEEG values. Sports-related psychological performance was estimated by Pearson's correlation coefficients, which revealed that a quick perceptual response to an acute bout of brain activity could predict an athlete's performance during competition (r = .584, p = .000). Additionally, Spearman's correlation coefficients were used to estimate athletes performance. The results revealed a strong relationship ( rsrs =.634, p = .000), which was derived from the summation of anxiety and perceptual response to an acute bout of brain activity. Consequently, the results of the present study can provide information to help staff coaches to choose the best performing players, representing an alternative method for accurately selecting key players in the competitive sports community.






Assessing Inter-Limb Asymmetries in Soccer Players: Magnitude, Direction and Association with Performance

We aimed to analyze the magnitude and direction of inter-limb asymmetries in ankle dorsiflexion range of motion (ROM), power (using iso-inertial devices) and a neuromuscular skill (change of direction). Secondarily, we aimed to determine the relationship between inter-limb asymmetry scores for each test and also between these scores and the scores for the different performance tests.





Scanning activity of elite footballers in match play: An eye-tracking analysis on the duration and visual information of scanning

The aim of this study was to examine the duration and information (number of teammates and opponents) of the players’ scanning behavior of four elite football midfield players in an 11 vs. 11 using mobile eye-tracking technology.





Latest research in football - week 27 - 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 Selected, Deselected, and Reselected: A Case Study Analysis of Attributes Associated With Player Reselection Following Closure of a Youth Soccer Academy

Reference: Front Sports Act Living. 2021 Mar 23;3:633124.  doi: 10.3389/fspor.2021.633124. eCollection 2021.

Authors: James H Dugdale, Allistair P McRobert, Viswanath B Unnithan 

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Summary: Considering the perceived benefit of early recruitment and the time and resources spent developing youth players, individuals released from talent development programmes are often re-recruited by rival academies. However, due to the contractual nature of many talent development programmes, limited empirical data exists on players deselected from (or reselected to) youth soccer academies. Adopting a novel case study approach, differences in skill, psychological, and physical attributes associated with reselection following closure of a junior-elite soccer academy were explored. Overall subjective coach ratings for skill, psychological, and physical abilities; subjective coach ratings for skill and psychological attributes; and physical fitness test performance of 79 junior-elite soccer players (U11-U17) were assessed as part of regular scheduled testing and monitoring practices prior to the academy closure. Reselection status was monitored and recorded for all players in the 6 months following the academy closure and was classified as a persistence/progression ("Reselected") or attrition ("Deselected") in playing level. Of the 79 released players, a total of 60 players (76%) were re-signed to a junior-elite academy within 6 months. Differences were observed for overall ratings of skill, psychological, and physical abilities in favor of the "Reselected" player group. "Reselected" players were also rated higher by coaches for all attributes categorized as skill and psychological, as well as performing better at all physical fitness tests. However, "Reselected" players were lesser in stature and body mass and less mature than "Deselected" players. Our findings suggest that reselection is not a product of anthropometric criteria and, therefore, a pathway for selection remains open for later maturing players. We also inform upon desirable qualities associated with player reselection and provide a case study approach of a unique, yet highly relevant, scenario for talent identification and development in youth soccer.



#2 Associations Between Variations in Accumulated Workload and Physiological Variables in Young Male Soccer Players Over the Course of a Season

Reference: Front Physiol. 2021 Mar 18;12:638180.  doi: 10.3389/fphys.2021.638180. eCollection 2021.

Authors: Hadi Nobari, Ana Ruivo Alves, Filipe Manuel Clemente, Jorge Pérez-Gómez, Cain C T Clark, Urs Granacher, Hassane Zouhal

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Summary: This study sought to analyze the relationship between in-season training workload with changes in aerobic power (VO2m ax ), maximum and resting heart rate (HR max and HR rest ), linear sprint medium (LSM), and short test (LSS), in soccer players younger than 16 years (under-16 soccer players). We additionally aimed to explain changes in fitness levels during the in-season through regression models, considering accumulated load, baseline levels, and peak height velocity (PHV) as predictors. Twenty-three male sub-elite soccer players aged 15.5 ± 0.2 years (PHV: 13.6 ± 0.4 years; body height: 172.7 ± 4.2 cm; body mass: 61.3 ± 5.6 kg; body fat: 13.7% ± 3.9%; VO2m ax : 48.4 ± 2.6 mL⋅kg-1⋅min-1), were tested three times across the season (i.e., early-season (EaS), mid-season (MiS), and end-season (EnS) for VO2m ax , HR max , LSM, and LSS. Aerobic and speed variables gradually improved over the season and had a strong association with PHV. Moreover, the HR max demonstrated improvements from EaS to EnS; however, this was more evident in the intermediate period (from EaS to MiS) and had a strong association with VO2m ax . Regression analysis showed significant predictions for VO2m ax [F ( 2, 20) = 8.18, p ≤ 0.001] with an R 2 of 0.45. In conclusion, the meaningful variation of youth players' fitness levels can be observed across the season, and such changes can be partially explained by the load imposed.



#3 Covid-19 and Football: Crisis Creates Opportunity

Reference: Polit Q. Jan-Mar 2021;92(1):132-138.  doi: 10.1111/1467-923X.12961. Epub 2021 Feb 3.

Authors: Kieran Maguire

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Summary: This article looks at the financial performance and position of English professional football before Covid-19 and the impact that the pandemic has had on the industry. It analyses revenue streams in different divisions, the dependency that clubs have on them and how they have changed as a result of the pandemic. The article also reviews key costs for football clubs, the extent to which they can be reduced, different business models that operate, and possible funding sources for the sport from third parties and within the industry.



#4 Comparison of the Morphological Characteristics of South African Sub-Elite Female Football Players According to Playing Position

Reference: Int J Environ Res Public Health. 2021 Mar 31;18(7):3603.  doi: 10.3390/ijerph18073603.

Authors: Anita Strauss 1 2, Martinique Sparks 2, Cindy Pienaar 2 3

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Summary: Limited information is available on the morphological characteristics of adult female footballers, therefore the aim of this article was to examine if there are position-specific differences in the morphological characteristics of sub-elite female football players and to establish normative standards for this level of female football players. The morphological features of 101 sub-elite female football players (age: 21.8 ± 2.7 years) were assessed. Twenty anthropometric sites were measured for body composition and somatotype. The average value of body fat percentage was 20.8 ± 5.7%. The somatotype of the overall group was 4.0-2.4-2.1. Significant (p ≤ 0.05) differences were found between goalkeepers and outfield players in morphological characteristics. Goalkeepers were taller (166.2 ± 8.4 cm), heavier (66.5 ± 5.1 kg), possessed the highest body fat percentage (17.2 ± 6.2%) and showed higher values for all skinfold (sum of 6 skinfolds = 125.6 ± 45.9 cm), breadth, girth and length measurements. However, there were very few practically worthwhile differences between the outfield positions. Positional groups did not differ (p ≤ 0.05) in somatotype characteristics either. The study suggests that at sub-elite level there are mainly differences between goalkeepers and outfield players, but outfield players are homogeneous when comparing morphological characteristics. These results may serve as normative values for future comparisons regarding the morphological characteristics of female football players.



#5 A Mixed-Methods Evaluation of CARE (Cancer and Rehabilitation Exercise): A Physical Activity and Health Intervention, Delivered in a Community Football Trust

Reference: Int J Environ Res Public Health. 2021 Mar 23;18(6):3327.  doi: 10.3390/ijerph18063327.

Authors: Zoe Rutherford 1 2, Stephen Zwolinsky 3, Nicky Kime 4, Andy Pringle 5

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Summary: With increasing cancer survivorship has come an increased necessity to support people living with cancer (PLWC) to have a good quality of life including being physically active. Using mixed methods, the current study aimed to use the RE-AIM evaluation framework (Reach, Effectiveness, Adoption, Implementation and Maintenance) to determine how the football community trust delivered CARE (Cancer and Rehabilitation Exercise) intervention was able to increase participants' physical activity in order to improve their quality of life and regain physiological and psychological function. Quantitative outcome data were collected at baseline, 3 and 6 months using the Cancer Physical Activity Standard Evaluation Framework questionnaire. Semi-structured focus groups (n = 5) captured participants' (n = 40) lived experience of the reach, effectiveness, adoption, implementation, and maintenance of CARE. Questionnaire data were analysed using repeated measures ANOVAs and qualitative data were thematically analysed. Following diagnosis, CARE was successful in providing participants with a unique and accessible opportunity to become or restart physically activity, by providing a local, socially supportive, and inclusive environment. This resulted in significant increases in physical activity (F(1.58, 23) = 5.98, p = 0.009), quality of life (QoL) (F(2,36) = 13.12, p = 0.000) and significant reductions in fatigue (F(1.57,31) = 11.19, p = 0.000) over 6 months. Participants also reported becoming more active, recovering physical function, regaining independence, and enhanced psychological well-being as a result of attending CARE. Key design features of CARE were also identified across RE-AIM. CARE, a football community trust delivered physical activity intervention was successful in significantly improving participants' QoL and in regaining the physical and psychological functioning of people living with cancer. Results suggest that maintaining engagement in CARE for 6 months and beyond can support people to maintain these changes. Engaging in robust evaluations such as this can help organizations to successfully secure future funding for their programs.



#6 How did three consecutive matches with extra time affect physical performance? A case study of the 2018 football Men's World Cup

Reference: Biol Sport. 2021 Mar;38(1):65-70.  doi: 0.5114/biolsport.2020.97668. Epub 2020 Aug 21.

Authors: Michał Kołodziejczyk, Paweł Chmura, Luka Milanovic, Marek Konefał, Jan Chmura, Andrzej Rokita, Marcin Andrzejewski

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Summary: The purpose of this study was to ascertain the effect of playing three consecutive matches with extra time (ET) on the physical performance of selected Croatian players in their subsequent match, the final of the 2018 Men's World Cup in Russia. The case study consisted of 4 players on the Croatian national team (16 observations) who had played in all three matches up to 120 min. The consecutive full time matches (90 minutes) and extra time (30 minutes) were compared. The analysis was conducted using data collected by an advanced motion analysis system known as STATS and from interviews with the strength and conditioning coach of the Croatian national team. The recorded variables used were: total distance covered [m], distances covered [m] at intensity ranges of 20-25 km/h and above 25 km/h, and number of sprints performed. All the studied parameters systematically increased in each match up to 90 minutes of play, reached their maximum values in the semi-final and then decreased in the final match. Compared to the first extra time period, in the third extra time period the players covered twice as much distance with an intensity of 20-25 km/h and above 25 km/h, and recorded twice as many sprints. This investigation shows that players in central positions on the pitch are able to maintain or even increase high and very high intensity activity in three consecutive matches with extra time. These data complement the developing body of literature relating to the influence of accumulation of match play with extra time periods on high level players.



#7 Incidence of cardiovascular events when watching intense football matches - sex differences

Reference: Acta Cardiol. 2021 Apr 8;1-7.  doi: 10.1080/00015385.2021.1908703. Online ahead of print.

Authors: Luka Matej Mahečić, Florijan Iljazović, Marjeta Mišigoj-Duraković, Zdravko Babić

Summary: FIFA World Cup represent one of the world's greatest phenomena. The spectators watch the matches of national teams with great emotional involvement. It is well documented fact that emotional stress can be a trigger of unwanted cardiovascular (CV) event. The aim of this retrospective study was to determine whether there had been an increase in the number of the emergency admissions for CVD in the Emergency Room and Clinic for Cardiovascular Diseases of the Sestre milosrdnice University Hospital Centre during and after the matches that the Croatian national team played in the FIFA World Cup 2018. The hospital's database was examined for the dates when Croatia played its matches, plus two more days after each match. An unexposed period that included the same dates in 2017 and 2019 was formed. 1093 cases were assessed. The incidence of CV admissions during the exposed period was 1.15 (95% confidence interval [CI]; 1.02 to 1.31) times higher than during the unexposed period. There was a 1.30 (95% CI; 1.1 to 1.54) times higher incidence in women compared to the unexposed period. Arrhythmias and angina pectoris were the CVDs that occurred more frequently in the exposed period. This study showed that watching Croatian national team's matches and cheering represented an additional risk for a CV incident, especially in women.



#8 Is Increased Kicking Leg Iliopsoas Muscle Tightness a Predictive Factor for Developing Spondylolysis in Adolescent Male Soccer Players?

Reference: Clin J Sport Med. 2021 Mar 12. doi: 10.1097/JSM.0000000000000920. 

Authors: Seira Takei, Suguru Torii, Shuji Taketomi, Soichiro Iwanuma, Michio Tojima, Mana Otomo, Satoshi Iizuka, Sakae Tanaka

Summary: The aim was to identify predictive risk factors of lumbar stress (LS) fracture developing from an asymptomatic stress reaction of the pedicle among adolescent male soccer players. Japanese adolescent male soccer players (n = 195) aged 12 to 13 years participated in this study. Height, body weight, body mass index, muscle tightness of both lower extremities (iliopsoas, hamstrings, and quadriceps), lumbar bone mineral content, developmental age, and lumbar lordosis angle were measured as baseline measurements. Players who were diagnosed with an asymptomatic stress reaction of the lumbar spine pedicle at baseline were followed; extension-based lumbar pain was defined 1 year after the baseline. The players were assigned to the LS fracture or control (CON) group at follow-up. At baseline, 40 boys were diagnosed with an asymptomatic stress reaction of the lumbar spine pedicle. The difference in muscle tightness between the kicking leg and supporting leg was significantly different (P = 0.012) between the LS (n = 16) and CON (n = 22) groups. Increase in iliopsoas muscle tightness in the kicking leg was a predictive risk factor of developing extension-based lumbar pain after adjusting for developmental age and body mass index (odds ratio, 1.54; 95% confidence interval, 1.05-2.27). Development of extension-based lumbar pain from an asymptomatic stress reaction of the pedicle among adolescent male soccer players was associated with increased iliopsoas muscle tightness of the kicking leg relative to that of the supporting leg.



#9 Clinical Risk Profile for a Second Anterior Cruciate Ligament Injury in Female Soccer Players After Anterior Cruciate Ligament Reconstruction

Reference: Am J Sports Med. 2021 Apr 15;363546521999109. doi: 10.1177/0363546521999109. 

Authors: Anne Fältström, Joanna Kvist, Natalia F N Bittencourt, Luciana D Mendonça, Martin Hägglund

Summary: The risk of a second anterior cruciate ligament (ACL) injury when participating in pivoting sports after ACL reconstruction is high. Risk factors associated with a second ACL injury are complex. The purpose was to investigate the combinations of various clinical risk factors associated with second ACL injury in female soccer players with a primary unilateral ACL reconstruction, using Classification and Regression Tree (CART) analysis. A total of 117 active female soccer players (mean ± SD age, 20 ± 2 years) were included. Athletes were enrolled 19 ± 9 months after ACL reconstruction and were prospectively followed for 2 years. At baseline, all players underwent assessment of knee and ankle joint range of motion (ROM), participated in functional tests (postural control, hop performance, and movement asymmetries in the lower limbs and trunk), and answered questionnaires (patient-reported knee function, knee-related quality of life, psychological and personality factors). A clinical prediction model using CART was developed. A total of 28 players (24%) sustained a second ACL injury (21 ipsilateral and 7 contralateral ruptures) while playing soccer. CART analysis selected 9 of 19 independent variables associated with second ACL injury: the 5-jump test, knee collapse on the non-ACL reconstructed leg in a drop vertical jump, tuck jump, limb symmetry index on side hop and the single hop for distance, side difference in ankle dorsiflexion ROM, and scores for the questionnaires ACL-Return to Sport After Injury and the Swedish Universities Scales of Personality subscales of Stress Susceptibility and Adventure Seeking. The accuracy of the model was 89%, with 100% sensitivity and 76% specificity. CART analysis indicated that the interaction of longer jumps in the 5-jump test (>916 cm) with more side difference in ankle dorsiflexion ROM (>-2.5°) and more knee valgus collapse in the nonreconstructed knee (>-1.4 cm) (relative risk, 4.03; 95% CI, 2.21-7.36) best predicted an increased likelihood of a second ACL injury. The risk profiles selected by CART could accurately identify female soccer players at high risk for a second ACL injury. There was an interaction between functional performance, clinical assessment, and psychological factors, and it is reasonable to include these factors in return-to-sport decisions and in athlete screening after ACL injury.



#10 Poor Validity of Functional Performance Tests to Predict Knee Injury in Female Soccer Players With or Without Anterior Cruciate Ligament Reconstruction

Reference: Am J Sports Med. 2021 Apr 12;3635465211002541.  doi: 10.1177/03635465211002541. 

Authors: Anne Fältström, Martin Hägglund, Henrik Hedevik, Joanna Kvist 

Summary: Various tests have been developed to evaluate athletes' functional performance and for use as screening tools for injury prediction. Further validation of their accuracy to predict injury is needed. The purpose was to investigate the validity of predetermined cutoffs used to differentiate between high- and low-risk players in different functional performance tests to predict (1) anterior cruciate ligament (ACL) injury or (2) severe traumatic knee injury in a cohort of female soccer players with a primary unilateral ACL reconstruction and a cohort of knee-healthy players. A total of 117 active female soccer players (mean age ± SD, 20 ± 2 years) an average of 19 ± 9 months after ACL reconstruction and 119 knee-healthy players (age, 19 ± 3 years) were prospectively followed up for 2 years for new knee injuries. At baseline, all players underwent tests to assess postural control (Star Excursion Balance Test), hop performance (single-leg hop for distance, side hop), and movement asymmetries in the lower limbs and trunk (drop vertical jump [DVJ], tuck jump). The predictive validity of the test cutoffs to identify players who would sustain an ACL injury or a severe traumatic knee injury (absence from soccer play, >28 days) was assessed. The risk ratio (RR), area under the receiver operating characteristic curve (AUC), sensitivity, and specificity were calculated. A total of 46 players (39%) with ACL reconstruction sustained 48 severe knee injuries, including 28 ACL ruptures. Of the knee-healthy players, 13 (11%) sustained 14 severe knee injuries, including 8 ACL ruptures. No association was found between the predetermined functional performance test cutoffs and the risk of a new ACL injury or severe knee injury in players with ACL reconstruction. In knee-healthy players, the only variable associated with future ACL injury was ≥6.5 cm knee valgus in the frontal plane (any knee) in the DVJ (RR, 4.93; 95% CI, 1.04-23.40; P = .045), but with only fair predictive validity (AUC, 0.7; sensitivity, 0.75; specificity, 0.65). In our cohorts of female soccer players, the validity of commonly used functional performance tests to predict new knee injuries was poor. Only knee valgus during the DVJ was associated with new ACL injuries in knee-healthy players, but with only fair predictive validity.



#11 Physiological Characteristics of Female Soccer Players and Health and Performance Considerations: A Narrative Review

Reference: Sports Med Review. 2021 Apr 12.  doi: 10.1007/s40279-021-01458-1. Online ahead of print.

Authors: Rebecca K Randell, Thomas Clifford, Barry Drust, Samantha L Moss, Viswanath B Unnithan, Mark B A De Ste Croix, Naomi Datson, Daniel Martin, Hannah Mayho, James M Carter, Ian Rollo 

Summary: Female soccer has seen a substantial rise in participation, as well as increased financial support from governing bodies over the last decade. Thus, there is an onus on researchers and medical departments to develop a better understanding of the physical characteristics and demands, and the health and performance needs of female soccer players. In this review, we discuss the current research, as well as the knowledge gaps, of six major topics: physical demands, talent identification, body composition, injury risk and prevention, health and nutrition. Data on female talent identification are scarce, and future studies need to elucidate the influence of relative age and maturation selection across age groups. Regarding the physical demands, more research is needed on the pattern of high-intensity sprinting during matches and the contribution of soccer-specific movements. Injuries are not uncommon in female soccer players, but targeting intrinsically modifiable factors with injury prevention programmes can reduce injury rates. The anthropometric and physical characteristics of female players are heterogeneous and setting specific targets should be discouraged in youth and sub-elite players. Menstrual cycle phase may influence performance and injury risk; however, there are few studies in soccer players. Nutrition plays a critical role in health and performance and ensuring adequate energy intake remains a priority. Despite recent progress, there is considerably less research in female than male soccer players. Many gaps in our understanding of how best to develop and manage the health and performance of female soccer players remain.



#12 Validity of a Rehab and Reconditioning Program Following an Adductor Longus Injury in Professional Soccer

Reference: J Sport Rehabil. 2021 Apr 9;1-6.  doi: 10.1123/jsr.2020-0360. Online ahead of print.

Authors: Sergio Jiménez-Rubio, José Luis Estévez Rodríguez, Archit Navandar

Summary: The high rates of adductor injuries and reinjuries in soccer have suggested that the current rehabilitation programs may be insufficient; therefore, there is a need to create prevention and reconditioning programs to prepare athletes for the specific demands of the sport. The aim of this study is to validate a rehab and reconditioning program (RRP) for adductor injuries through a panel of experts and determine the effectiveness of this program through its application in professional soccer. A 20-item RRP was developed, which was validated by a panel of experts anonymously and then applied to 12 injured male professional soccer players. Eight rehabilitation fitness coaches (age = 33.25 [2.49] y) and 8 academic researchers (age = 38.50 [3.74] y) with PhDs in sports science and/or physiotherapy. The RRP was applied to 12 male professional players (age = 23.75 [4.97] y; height = 180.56 [8.41] cm; mass = 76.89 [3.43] kg) of the Spanish First and Second Division (La Liga). The experts validated an indoor and on-field reconditioning program, which was based on strengthening the injured muscle and retraining conditional capacities with the aim of reducing the risk of reinjury. Aiken V for each item of the program and number of days taken by the players to return to full team training was taken as outcome measures. The experts evaluated all items of the program very highly as seen from Aiken V values between 0.77 and 0.94 (range: 0.61-0.98) for all drills, and the return to training was in 13.08 (±1.42) days. This RRP following an injury to the adductor longus was validated by injury experts, and initial results suggested that it could permit a faster return to team training.



#13 Assessing Post-Game Emotions in Soccer Teams: The Role of Distinct Emotional Dynamics

Reference: Eur J Sport Sci. 2021 Apr 9;1-22.  doi: 10.1080/17461391.2021.1916079. Online ahead of print.

Authors: James L Rumbold, James A Newman, David Foster, Daniel J A Rhind, Jack Phoenix, Lorcan Hickey

Summary: This study examined the relationships between team (n = 10) and player post-game emotions following two consecutive games. In addition, the relationship between emotional contagion susceptibility and player post-game emotions was assessed. Applying an experience sampling methodology, male amateur and semi-professional soccer players (N = 114, Mage = 25.46 years, SD = 9.24) completed a sport emotion questionnaire shortly after the conclusion of two competitive games. Participants also completed a dispositional emotional contagion questionnaire prior to post-game data collection. Multilevel regressions revealed that teams' collective post-game emotions were strongly associated with players' post-game emotions, after accounting for within- (e.g., time, game outcome) and between-person (e.g., formal leaders, emotional contagion susceptibility) differences. In addition, partial support was found to indicate that emotional contagion susceptibility was associated with players' post-game emotions. In this context of soccer, the findings suggest that collective emotions following a game are more indicative of individual players' emotions than an individual's general tendency to mimic the emotions of others. From an applied perspective, the findings demonstrate the importance of coaches and players being mindful of the team's emotional climate after a game and the impact it may have on players, especially when that climate is negative.





Is there meaningful influence from situational and environmental factors on the physical and technical activity of elite football players?

The study aimed to identify the effects of situational (match location, match outcome and strength of team/opponent team) and environmental (ambient temperature, relative humidity, WBGT, ground and weather condition) factors on the physical and technical activity of elite football on individual playing positions.





Hip Abductor Muscle Strength Deficit as a Risk Factor for Inversion Ankle Sprain in Male College Soccer Players

The purpose was to identify risk factors for inversion ankle sprains among male collegiate soccer players.





Latest research in football - week 26 - 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 Timing return-to-competition: a prospective registration of 45 different types of severe injuries in Germany's highest football league

Reference: Arch Orthop Trauma Surg. 2021 Mar 29.  doi: 10.1007/s00402-021-03854-8. Online ahead of print.

Authors: Werner Krutsch, Clemens Memmel, Volker Alt, Volker Krutsch, Tobias Tröß, Karen Aus der Fünten, Tim Meyer

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Summary: Many professional football players sustain at least one severe injury over the course of their career. Because detailed epidemiological data on different severe injuries in professional football have been missing so far, this study describes the frequency and return-to-competition (RTC) periods of different types of severe football injuries. This epidemiological investigation is a prospective standardised injury analysis based on national media longitudinal registration. Injuries were classified according to the consensus statement by Fuller et al. (2006). The analysis includes injuries sustained by players of the first German football league during the seasons 2014-2015 to 2017-2018. Overall, 660 severe injuries were registered during the four seasons (mean 165 per season; 9.2 per season per team; incidence in 1000 h: 0.77). The body region most frequently affected by severe injury was the knee (30.0%; 49.5 injuries per season/SD 13.2) followed by the thigh (26.4%; 43.5 injuries/SD 4.2) and the ankle (16.7%; 27.5 injuries/SD 5.0). The distribution of injuries over the course of a season showed a trend for ACL ruptures to mainly occur at the beginning of a season (45.8%), overuse syndromes such as achillodynia (40.9%) and irritation of the knee (44.4%) during the winter months and severe muscle and ankle injuries at the end of a season. ACL ruptures showed the longest RTC durations (median 222 days). This study presents detailed epidemiological data on severe injuries in professional football. The body region most frequently affected by severe injuries was the knee. Several types of severe injuries showed a seasonal injury pattern. The appropriate timing of RTC after an injury is one of the most important and complex decisions to be made. This study provides information on the typical time loss due to specific severe football injuries, which may serve as a guideline.



#2 The Poor "Wealth" of Brazilian Football: How Poverty May Shape Skill and Expertise of Players

Reference: Front Sports Act Living. 2021 Mar 11;3:635241.  doi: 10.3389/fspor.2021.635241. eCollection 2021.

Authors: Luiz Uehara, Mark Falcous, Chris Button, Keith Davids, Duarte Araújo, Adelgício Ribeiro de Paula, John Saunders

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Summary: Worldwide, 1.3 billion people live in Poverty, a socio-economic status that has been identified as a key determinant of a lack of sports participation. Still, numerous athletes around the world have grown up in underprivileged socio-economic conditions. This is the case in Brazil, a country with around 13.5 million impoverished citizens, yet, over decades, many of its best professional footballers have emerged from its favelas. In this article, we explore the role of the socio-cultural-economic constraints in shaping the development of skill and expertise of Brazilian professional football players. The methodological and epistemological assumptions of the "Contextualized Skill Acquisition Research" (CSAR) approach are used as an underpinning framework for organizing and analyzing data. Results suggested that, at the exosystemic level of Brazilian society, Poverty emerges as an influential constraint that can potentially enrich football development experiences of Brazilian players. Poverty, however, is not the direct causation of outstanding football skill development. Rather, from the perspective of ecological dynamics, Poverty creates specific contexts that can lead to the emergence of physical as well as socio-cultural environment constraints (e.g., Pelada, Malandragem) that can shape affordances (opportunities) for skill acquisition. These ideas suggest the need to ensure that environmental constraints can support people to amuse themselves cheaply, gain access to employment opportunities and maintain health and well-being through (unstructured and more structured) sport and physical activities in dense urban environments such as favelas, inner city areas, and banlieues. For this purpose, design of open play areas and even parkour installations can provide affordances landscapes for physical activity and sports participation in urban settings.



#3 Head impact forces in blind football are greater in competition than training and increased cervical strength may reduce impact magnitude

Reference: Int J Inj Contr Saf Promot. 2021 Mar 30;1-7.  doi: 10.1080/17457300.2021.1905667. 

Authors: Daniel Fitzpatrick, Peter Thompson, Courtney Kipps, Nick Webborn

Summary: Paralympic Blind Association Football has the highest rate of injury of any Paralympic sport and head injuries are common. This study aims to quantify head impact incidence and magnitude in Blind Football, and to examine contributing factors. This Observational study based on a Blind Football Team comprising seven male athletes 28.63 years (SD 9.74, range 16-46) over 6 months. Head mounted impact sensors were used to measure the frequency and location of impacts, as well as their linear acceleration and rotational velocity. Cervical isometric strength and proprioception was measured. There were 374 impacts recorded in 212.5 athlete hours. There was a higher rate of impacts in matches than training (Incidence Risk Ratio 2.58, 95% CI 2.01-3.30). Greater cervical strength was associated with reduced linear acceleration of impacts (R2 = 0.1912, p = .020). Blind Football players are exposed to a greater number of head impacts in matches than training. Neck muscle strength may influence magnitude of head impact forces in this sport but further study is required to further investigate.



#4 How does spectator presence affect football? Home advantage remains in European top-class football matches played without spectators during the COVID-19 pandemic

Reference: PLoS One. 2021 Mar 31;16(3):e0248590.  doi:10.1371/journal.pone.0248590. eCollection 2021.

Authors: Fabian Wunderlich, Matthias Weigelt, Robert Rein, Daniel Memmert

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Summary: The present paper investigates factors contributing to the home advantage, by using the exceptional opportunity to study professional football matches played in the absence of spectators due to the COVID-19 pandemic in 2020. More than 40,000 matches before and during the pandemic, including more than 1,000 professional matches without spectators across the main European football leagues, have been analyzed. Results support the notion of a crowd-induced referee bias as the increased sanctioning of away teams disappears in the absence of spectators with regard to fouls (p < .001), yellow cards (p < .001), and red cards (p < .05). Moreover, the match dominance of home teams decreases significantly as indicated by shots (p < .001) and shots on target (p < .01). In terms of the home advantage itself, surprisingly, only a non-significant decrease is found. While the present paper supports prior research with regard to a crowd-induced referee bias, spectators thus do not seem to be the main driving factor of the home advantage. Results from amateur football, being naturally played in absence of a crowd, provide further evidence that the home advantage is predominantly caused by factors not directly or indirectly attributable to a noteworthy number of spectators.



#5 The Self-Regulation of Learning - Self-Report Scale for Sport Practice: Validation of an Italian Version for Football

Reference: Front Psychol. 2021 Mar 15;12:604852.  doi: 10.3389/fpsyg.2021.604852. eCollection 2021.

Authors: Eleonora Reverberi, Caterina Gozzoli, Chiara D'Angelo, Margherita Lanz, Angela Sorgente

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Summary: Self-regulation of learning (SRL) is a key psychological factor that supports young athletes aiming to reach the elite level by promoting their involvement in deliberate practice. We contributed to the validation of the Italian version of the Bartulovic et al. (2017) Self-Regulation of Learning - Self-Report Scale for Sport Practice by testing its factorial structure, reliability, and measurement invariance among elite and non-elite football players, involving 415 male professional, semi-professional, and amateur youth academy players (M age = 16.2, SD = 1.51). The original six-factor structure (planning, reflection, effort, self-efficacy, self-monitoring, and evaluation) did not fit the data well and a five-factor solution (where self-monitoring and evaluation items load on the same factor, named "self-supervision") was a better fit. This five-factor solution was measurement invariant across groups of elite and non-elite athletes. We found that elite athletes scored significantly higher than non-elite ones in each SRL subprocess. Implications for future validation studies and for the use of this tool are discussed.



#6 Using Submaximal Exercise Heart Rate for Monitoring Cardiorespiratory Fitness Changes in Professional Soccer Players: A Replication Study

Reference: Int J Sports Physiol Perform. 2021 Mar 31;1-7.  doi: 10.1123/ijspp.2020-0554. Online ahead of print.

Authors: Stefan Altmann, Rainer Neumann, Sascha Härtel, Alexander Woll, Martin Buchheit

Summary: The purpose was to assess the value of monitoring changes in fitness in professional soccer players, using changes in heart rate at submaximal intensity (HR12km/h) over the velocity at a lactate concentration of 4 mmol/L (v4mmol/L). The authors reexamined (1) a range of threshold magnitudes, which may improve detecting substantial individual changes and (2) the agreement between changes in these 2 variables. On at least 2 occasions during different moments of the season, 97 professional soccer players from Germany (first, second, and fourth division) completed an incremental test to determine HR12km/h and v4mmol/L. Optimal thresholds for changes in HR12km/h and v4mmol/L were assessed, using various methods (eg, smallest worthwhile change + typical error [TE], successive reiterations approach). Agreement between both variable changes was examined for the whole sample (225 comparisons), 4 different subgroups (depending on the moment of the season), and in an individual over 6 years (n = 23 tests). Changes of 4.5% and 6.0% for HR12km/h and v4mmol/L, respectively, were rated as optimal to indicate substantial changes in fitness. Depending on the (sub)groups analyzed, these thresholds yielded 0% to 2% full mismatches, 22% to 38% partial agreements, and 60% to 78% full agreements in terms of fitness change interpretation between both variables. When lactate sampling during incremental tests is not possible, practitioners willing to monitor adult professional soccer players' (Germany; first, second, and fourth division) training status can confidently implement short, 3-minute submaximal runs, with 4.5% changes in HR12km/h being indicative of true substantial fitness changes, with 60% to 78% accuracy. Future studies should investigate the potential role of confounding factors of HR12km/h to improve changes in fitness prediction.



#7 Muscle activity of cutting manoeuvres and soccer inside passing suggests an increased groin injury risk during these movements

Reference: Sci Rep. 2021 Mar 31;11(1):7223.  doi: 10.1038/s41598-021-86666-5.

Authors: Thomas Dupré, Julian Tryba, Wolfgang Potthast

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Summary: Cutting manoeuvres and inside passing are thought to increase the risk of sustaining groin injuries. But both movements have received little research attention in this regard. The purpose of this study was to investigate the muscle activity of adductor longus and gracilis as well as hip and knee joint kinematics during [Formula: see text]-cutting and inside passing. Thirteen male soccer players were investigated with 3D-motion capturing and surface electromyography of adductor longus and gracilis while performing the two movements. Hip and knee joint kinematics were calculated with AnyBody Modelling System. Muscle activity of both muscles was significantly higher during the cutting manoeuvre compared to inside passing. Kinematics showed that the highest activity occurred during phases of fast muscle lengthening and eccentric contraction of the adductors which is known to increase the groin injury risk. Of both movements, cutting showed the higher activity and is therefore more likely to cause groin injuries. However, passing might also increase the risk for groin injuries as it is one of the most performed actions in soccer, and therefore most likely causes groin injuries through overuse. Practitioners need to be aware of these risks and should prepare players accordingly through strength and flexibility training.



#8 Effect of a Shock Micro-Cycle on Biochemical Markers in University Soccer Players

Reference: Int J Environ Res Public Health. 2021 Mar 30;18(7):3581.  doi: 10.3390/ijerph18073581.

Authors: Diana García-Cardona, Patricia Landázuri, Oscar Sánchez-Muñoz

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Summary: This study aimed to examine various biochemical biomarkers changes during a shock micro-cycle in soccer players from a university team. The study had 22 players (age: 22 ± 3 years; body mass: 68.6 ± 7.1 kg; height: 1.73 ± 0.07 m). The study measured total cholesterol (TC), triglycerides (TG), cholesterol linked to high-density lipoproteins (HDL), low-density lipoproteins (LDL), very low density lipoproteins (VLDL), arterial index (AI), creatine kinase (CK), glutamate-oxalacetate-transaminase (GOT), glutamate-pyruvate-transaminase (GPT), creatinine (Cr), catalase (CAT), superoxide dismutase (SOD), cytokines IL6 and TNFα, total antioxidant capacity (Cap antiox tot), hemolysis percentage and glomerular filtration rate (GFR); measurements were conducted during a shock micro-cycle. The lipid profile variables had no statistical significance when compared on day 1 with day 14. Except for TNFα, the other biomarkers compared with day one had progressive increments until day seven, with a subsequent reduction on day 14; however, none of the biomarkers returned to baseline values despite this decrease. The data shown herein suggest the need to research these biomarkers in distinct types of mesocycles, exercise, intensity, load, and duration to diminish fatigue and improve athlete performance.



#9 Body Physique, Body Composition, Physical Performance, Technical and Tactical Skills, Psychological Development, and Club Characteristics of Young Male Portuguese Soccer Players: The INEX Study

Reference: Int J Environ Res Public Health. 2021 Mar 30;18(7):3560.  doi: 10.3390/ijerph18073560. DOI: 10.3390/ijerph18073560

Authors: Maryam Abarghoueinejad, Daniel Barreira, Cláudia Dias, Eduardo Guimarães, Adam D G Baxter-Jones, José Maia

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Summary: Youth soccer performance is multifaceted, includes physical growth, biological maturation, and physical fitness, and is linked to the sporting environment to which the players are exposed. We aim to describe age-related associations in body physique, body composition, physical performance technical and tactical skills, psychological and club characteristics of male soccer players aged 12 to 14 years. A total of 157 male soccer players clustered into three age-cohorts (12, 13 and 14 years) were recruited from six soccer clubs. Anthropometric, body composition and body physique, biological maturation, physical performance, skill/game proficiency data, psychological characteristics, and clubs' characteristics were collected. Group means were compared using analysis of variance and covariance. Fourteen years old players were significantly taller, heavier, leaner, faster, stronger, and technically more skilled than their younger peers (p < 0.05). Differences in physical performance and technical skills (p < 0.05) were found between age groups when adjusting for confounders of soccer training and biological maturation. No significant differences (p > 0.05) between age groups were found in psychological domains. Our findings suggest that age, biological maturation, and training volume are key factors influencing young soccer players' performance and development. Further, clubs' conditions provide players with ample resources for their success in training and competition.



#10 Training Design, Performance Analysis, and Talent Identification-A Systematic Review about the Most Relevant Variables through the Principal Component Analysis in Soccer, Basketball, and Rugby

Reference: Int J Environ Res Public Health. 2021 Mar 5;18(5):2642.  doi: 10.3390/ijerph18052642.

Authors: José Pino-Ortega, Daniel Rojas-Valverde, Carlos D Gómez-Carmona, Markel Rico-González

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Summary: Since the accelerating development of technology applied to team sports and its subsequent high amount of information available, the need for data mining leads to the use of data reduction techniques such as Principal Component Analysis (PCA). This systematic review aims to identify determinant variables in soccer, basketball and rugby using exploratory factor analysis for, training design, performance analysis and talent identification. Three electronic databases (PubMed, Web of Science, SPORTDiscus) were systematically searched and 34 studies were finally included in the qualitative synthesis. Through PCA, data sets were reduced by 75.07%, and 3.9 ± 2.53 factors were retained that explained 80 ± 0.14% of the total variance. All team sports should be analyzed or trained based on the high level of aerobic capacity combined with adequate levels of power and strength to perform repeated high-intensity actions in a very short time, which differ between team sports. Accelerations and decelerations are mainly significant in soccer, jumps and landings are crucial in basketball, and impacts are primarily identified in rugby. Besides, from these team sports, primary information about different technical/tactical variables was extracted such as (a) soccer: occupied space, ball controls, passes, and shots; (b) basketball: throws, rebounds, and turnovers; or (c) rugby: possession game pace and team formation. Regarding talent identification, both anthropometrics and some physical capacity measures are relevant in soccer and basketball. Although overall, since these variables have been identified in different investigations, further studies should perform PCA on data sets that involve variables from different dimensions (technical, tactical, conditional).



#11 Control Deficits, Conditioning Factors, and Playing through Pain and Injury among Iranian Professional Soccer Players

Reference: Int J Environ Res Public Health. 2021 Mar 25;18(7):3387.  doi: 10.3390/ijerph18073387.

Authors: Saeed Kabiri, Jaeyong Choi, Seyyedeh Masoomeh Shamila Shadmanfaat, Julak Lee

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Summary: Playing through pain and injury is a common and accepted behavior in the athletic realm. The purpose of this research was to apply Tittle's control balance theory to explain why athletes engage in playing through pain and injury despite its risky nature. We hypothesized that playing through pain and injury is a form of submission described by Tittle and that it can be predicted by the concept of control deficit. To this end, we collected and used data from a sample of 410 professional soccer players from Guilan province, Iran, and tested several propositions derived from control balance theory. Hierarchical linear regression was used to analyze the data. The study findings demonstrate that players with more control deficits are more likely to play through pain and injury. This relationship is conditioned by self-control, opportunity, motivation, perceived benefits, and provocations. For example, the relationship between control deficit and playing through pain and injury is stronger for those with lower self-control. Our findings support the utility of control balance theory in explaining an act of submission (i.e., playing through pain and injury).



#12 Epidemiology of Injuries in First Division Spanish Women's Soccer Players

Reference: Int J Environ Res Public Health. 2021 Mar 15;18(6):3009.  doi: 10.3390/ijerph18063009.

Authors: Rodrigo Martín-San Agustín, Francesc Medina-Mirapeix, Andrea Esteban-Catalán, Adrian Escriche-Escuder, Mariana Sánchez-Barbadora, Josep C Benítez-Martínez

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Summary: The epidemiology of injuries in female soccer has been studied extensively in several national leagues. Even so, data on the first division Spanish league are limited. The objective of this study was to describe the epidemiology of the first division of the Spanish Women's Soccer League and to analyze data in relation to game position, circumstance, or the moment of injury. Fifteen teams and 123 players participated in the study. Players' characteristics and their injuries (location, type, diagnosis, circumstance, and moment) were collected. Injuries were described by their frequencies (number and percentage) and incidence rates (IR) with 95% confidence intervals (CIs). Lower limb injuries accounted for 86.8% of total injuries. Anterior cruciate ligament (ACL) and meniscus injuries occurred in totality in non-contact circumstance (0.35/1000 h; 95% CI, 0.18 to 0.62 and 0.23/1000 h; 95% CI, 0.10 to 0.45, respectively). Match injury IRs (19.02/1000 h; 95% CI, 14.89 to 23.97) were significantly higher than training (1.70/1000 h; 95% CI, 1.27 to 2.22). As a conclusion, structures such as the ACL or meniscus are most commonly injured in the non-contact circumstance in the first division of the Spanish Women's Soccer League. In addition, match situations involve a greater risk of injury than training, increasing the risk to the ankle and knee injuries as the season progresses.



#13 Effects of the Small-Sided Soccer Games on Blood Pressure in Untrained Hypertensive Adults: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Reference: Healthcare (Basel). 2021 Mar 18;9(3):345.  doi: 10.3390/healthcare9030345.

Authors: Filipe Manuel Clemente, Rodrigo Ramirez-Campillo, Hugo Sarmento

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Summary: This systematic review with meta-analysis was conducted to assess the effects of small-sided games (SSGs)-based programs on the systolic and diastolic blood pressure of untrained hypertensive adults. The data sources utilized were Web of Science, Scopus, SPORTDiscus, and PubMed. The eligibility criteria were: (i) randomized controlled trials including a control group and an intervention group exclusively using soccer SSGs; (ii) intervention and control groups including an untrained hypertensive adult population; (iii) articles written in English; and (iv) only full-text and original articles. The database search initially identified 241 titles. From those, five articles were eligible for the systematic review and meta-analysis. The included randomized controlled studies involved five individual experimental groups and 88 participants, and 68 participants in the five control groups. The results showed a large and beneficial effect of SSG on systolic (ES = 1.69; 95% CI = 0.71 to 2.66; p = 0.001; I2 = 85.2%; Egger's test p = 0.101) and diastolic blood pressure (ES = 2.25; 95% CI = 1.44 to 3.06; p < 0.001; I2 = 74.8%; Egger's test p = 0.118) when compared to the control groups. The findings of the current systematic review and meta-analysis revealed consistent beneficial effects of recreational soccer SSGs on untrained men and women from the hypertensive population, although high levels of heterogeneity.



#14 Data Mining to Select Relevant Variables Influencing External and Internal Workload of Elite Blind 5-a-Side Soccer

Reference: Int J Environ Res Public Health. 2021 Mar 18;18(6):3155.  doi: 10.3390/ijerph18063155.

Authors: José M Gamonales, Kiko León, Daniel Rojas-Valverde, Braulio Sánchez-Ureña, Jesús Muñoz-Jiménez

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Summary: Data mining has turned essential when exploring a large amount of information in performance analysis in sports. This study aimed to select the most relevant variables influencing the external and internal load in top-elite 5-a-side soccer (Sa5) using a data mining model considering some contextual indicators as match result, body mass index (BMI), scoring rate and age.  A total of 50 top-elite visually impaired soccer players (age 30.86 ± 11.2 years, weight 77.64 ± 9.78 kg, height 178.48 ± 7.9 cm) were monitored using magnetic, angular and rate gyroscope (MARG) sensors during an international Sa5 congested fixture tournament.; Fifteen external and internal load variables were extracted from a total of 49 time-related and peak variables derived from the MARG sensors using a principal component analysis as the most used data mining technique. The principal component analysis (PCA) model explained 80% of total variance using seven principal components. In contrast, the first principal component of the match was defined by jumps, take off by 24.8% of the total variance. Blind players usually performed a higher number of accelerations per min when losing a match. Scoring players execute higher DistanceExplosive and Distance21-24 km/h. And the younger players presented higher HRAVG and AccMax. The influence of some contextual variables on external and internal load during top elite Sa5 official matches should be addressed by coaches, athletes, and medical staff. The PCA seems to be a useful statistical technique to select those relevant variables representing the team's external and internal load. Besides, as a data reduction method, PCA allows administrating individualized training loads considering those relevant variables defining team load behavior.



#15 Influence of Size and Maturity on Injury in Young Elite Soccer Players

Reference: Int J Environ Res Public Health. 2021 Mar 18;18(6):3120.  doi: 10.3390/ijerph18063120.

Authors: Natascia Rinaldo, Emanuela Gualdi-Russo, Luciana Zaccagni

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Summary: The involvement of pre-adolescents in soccer is becoming more and more frequent, and this growing participation generates some concerns about the potential factors for sports injuries. The purpose of this study was to investigate sports injuries in younger (U9-U11) and older (U12-U13) children playing soccer at an elite level, analyzing potential anthropometric and maturity risk factors. A total of 88 elite soccer players aged 9-13 years were investigated. Weight, stature, and sitting height were measured at the start and at the end of the competitive season, computing the relative growth velocities. Additional body composition parameters were taken during a second survey. Maturity offset was calculated using predictive equations based on anthropometric traits such as years from age at peak height velocity (YPHV). Injuries suffered during the competitive season were recorded. Maturity and some anthropometric characteristics were significantly different according to the presence or absence of injuries among the players. Multiple logistic regression revealed that YPHV, body mass index (BMI), and calf muscle area were the factors most significantly correlated with injuries. Players with increased BMI, with decreased calf muscle area, and who were closer to their peak height velocity, were at a higher risk of injury. Findings showed that a monitoring program of anthropometric characteristics taking into account the maturational stage needs to be developed to prevent injuries.



#16 A Meta-Analytical Comparison of the Effects of Small-Sided Games vs. Running-Based High-Intensity Interval Training on Soccer Players' Repeated-Sprint Ability

Reference: Int J Environ Res Public Health. 2021 Mar 9;18(5):2781. doi: 10.3390/ijerph18052781.

Authors: Filipe Manuel Clemente, Rodrigo Ramirez-Campillo, José Afonso, Hugo Sarmento, Thomas Rosemann, Beat Knechtle

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Summary: This systematic review with a meta-analysis was conducted to compare the effects of small-sided games (SSGs)-based interventions with the effects of running-based high-intensity interval training (HIIT) interventions on soccer players' repeated sprint ability (RSA). The data sources utilized were Web of Science, Scopus, SPORTDiscus, and PubMed. The study eligibility criteria were: (i) parallel studies (SSG-based programs vs. running-based HIIT) conducted in soccer players with no restrictions on age, sex, or competitive level; (ii) isolated intervention programs (i.e., only SSG vs. only running-based HIIT as individual forms) with no restrictions on duration; (iii) a pre-post outcome for RSA; (iv) original, full-text, peer-reviewed articles written in English. An electronic search yielded 513 articles, four of which were included in the present study. There was no significant difference between the effects of SSG-based and HIIT-based training interventions on RSA (effect size (ES) = 0.30; p = 0.181). The within-group analysis revealed no significant effect of SSG-based training interventions (ES = -0.23; p = 0.697) or HIIT-based training interventions (ES = 0.08; p = 0.899) on RSA. The meta-comparison revealed that neither SSGs nor HIIT-based interventions were effective in improving RSA in soccer players, and no differences were found between the two types of training. This suggests that complementary training may be performed to improve the effects of SSGs and HIIT. It also suggests that different forms of HIIT can be used because of the range of opportunities that such training affords.



#17 Characteristics of Selected Somatic and Motor Abilities of Youth Soccer Players with Diabetes Type 1 Treated with Insulin Pump Therapy

Reference: Int J Environ Res Public Health. 2021 Mar 27;18(7):3493.  doi: 10.3390/ijerph18073493.

Authors: Magdalena Krzykała, Katarzyna Domaszewska, Małgorzata Woźniewicz-Dobrzyńska, Jakub Kryściak, Agata Konarska, Aleksandra Araszkiewicz, Dorota Zozulińska-Ziółkiewicz, Andrzej Gawrecki, Grzegorz Biegański, Jan M Konarski

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Summary: Long-term insulin treatment can slow the growth process and decrease physical fitness level in children. In diabetic children, these two developments should be constantly monitored. The aim of the present study was to examine differences in somatic and physical fitness characteristics between soccer-training boys with type 1 diabetes and healthy boys of the same age (reference values based on Polish population norms for somatic and motor parameters). The participants were 94 boys (8-17 years), diagnosed with diabetes, who participated in soccer training on a regular basis and received routine medical care. The study involved (a) anthropometric and body composition measurements, (b) general motor ability assessments, and (c) comparison of those characteristics with the healthy Polish population. The diabetic boys were found to have lower levels of almost all somatic traits and motor abilities as compared with the healthy boys (p ≤ 0.05). Handgrip strength was a variable with the smallest difference between the two groups. The observed differences indicate the necessity to design an appropriate control and assessment system based on simple medical and fitness field tests for diabetic children and adolescents. It will allow optimizing advanced training as well as minimize health risks before, during, or after exercise.



#18 Muscle Oxygen Desaturation and Re-Saturation Capacity Limits in Repeated Sprint Ability Performance in Women Soccer Players: A New Physiological Interpretation

Reference: Int J Environ Res Public Health. 2021 Mar 27;18(7):3484.  doi: 10.3390/ijerph18073484.

Authors: Aldo A Vasquez-Bonilla, Alba Camacho-Cardeñosa, Rafael Timón, Ismael Martínez-Guardado, Marta Camacho-Cardeñosa, Guillermo Olcina

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Summary: Muscle oxygen consumption could provide information on oxidative metabolism in women soccer players. Therefore, the objective of this study was to analyze muscle oxygenation dynamics during repeated sprint ability (RSA): (8 sprint × 20 s recovery) by near-infrared spectroscopy (NIRS). The sample was made up of 38 professional women soccer players. To measure the external load, the best time, worst time, average time, individual speed, sprint decrement, and power were assessed. In connection with the internal load, the desaturation (sprint) and re-saturation (recovery) rates, as well as the oxygen extraction (∇%SmO2) in the gastrocnemius muscle and maximum heart rate (%HRmax) were measured. A repeated measures statistic was applied based on the inter-individual response of each subject from the baseline versus the other sprints, with linear regression and nonlinear regression analyses between variables. There was an increase in the SmO2: desaturation rate after four sprints (Δ = 32%), in the re-saturation rate after six sprints (Δ = 89%), and in ∇%SmO2 after four sprints (Δ = 72.1%). There was a linear association between the rates of desaturation and re-saturation relationships and the worst time (r = 0.85), and a non-linear association between ∇%SmO2 and speed (r = 0.89) and between ∇%SmO2 and the sprint decrease (r = 0.93). The progressive increase in SmO2 during RSA is a performance limitation to maintain a high speed; it depends on the capacity of fatigue resistance. Therefore, monitoring the muscle oxygenation dynamics could be a useful tool to evaluate the performance in women soccer players.






Training Load in Different Age Category Soccer Players and Relationship to Different Pitch Size Small-Sided Games

This study sought to evaluate the training load in different age category soccer players associated with distinct pitch size small-sided games (SSGs).





Muscle Damage Biomarkers in Congestion Weeks in English Premier League Soccer Players: A Prospective Study for Consecutive Seasons

The current study was conducted to compare muscle damage biomarkers in single- vs. multi-match weeks in elite soccer players for two consecutive seasons. A secondary objective was to analyze the influence of playing position and exposure time on muscle damage in single- vs. multimatch weeks.





Latest research in football - week 25 - 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 Seasonal training and match load and micro-cycle periodization in male Premier League academy soccer players

Reference: J Sports Sci. 2021 Mar 24;1-12.  doi: 10.1080/02640414.2021.1899610. Online ahead of print.

Authors: Marcus P Hannon, Nicholas M Coleman, Lloyd J F Parker, John McKeown, Viswanath B Unnithan, Graeme L Close, Barry Drust, James P Morton

Summary: We quantified on pitch external loading of English Premier League (EPL) academy soccer players (n=76; U12-U18 age groups) over an entire competitive season. Mean accumulative weekly duration and total distance, respectively, was similar in the U12 (329±29 min; 19.9±2.2 km), U13 (323±29 min; 20.0±2.0 km) and U14 (339±25 min; 21.7±2.0 km; P>0.05 for all comparisons) age-groups, though all teams were less than U15 (421±15 min; 26.2±2.1 km), U16 (427±20 min; 25.9±2.5 km) and U18 (398±30 min; 26.1±2.6 km) players (P<0.05 for all comparisons). Mean weekly high-speed running and sprint distance was not different between U12 (220±95 m and 6±9 m respectively), U13 (331±212 m and 6±27 m) and U14 (448±193 m and 21±29 m) age-groups (P>0.05 for all pairwise comparisons) though all squads were less than U15 (657±242 m and 49±98 m), U16 (749±152 m and 95±55 m) and U18 (979±254 m and 123±56 m) age-groups (P<0.05 for all pairwise comparisons). Data demonstrate that absolute weekly training volume in EPL academy soccer players increases throughout the academy pathway. Furthermore, although U16-U18 players are capable of achieving similar training and match volumes as previously reported in adult EPL players, they do not yet achieve the absolute intensities of adult EPL players



#2 Strength development according with age and position: a 10-year study of 570 soccer players

Reference: BMJ Open Sport Exerc Med. 2021 Mar 5;7(1):e000927. doi: 10.1136/bmjsem-2020-000927. eCollection 2021.

Authors: Robson Dias Scoz, Bruno Mazziotti Oliveira Alves, Ricardo Lima Burigo, Edgar Ramos Vieira, Luciano Maia Alves Ferreira, Rubens Alexandre da Silva, Rogerio Pessoto Hirata, Cesar Ferreira Amorim

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Summary: The purpose of this study was to compare the isokinetic peak torque profiles from the quadriceps and hamstrings muscles during concentric and eccentric contractions in elite Brazilian soccer players across different field positions and age categories. Our hypothesis was that soccer players from different field positions are subjected to different ageing-related effects on their isokinetic peak torque. This is a retrospective study based on professional elite-level soccer players between the years 2009 and 2019. It included 570 adult males who played for at least 5 years on first or second Brazilian divisions. Playing positions were divided as: goalkeepers, defenders, sidebacks, midfielders and forwards. Age categories were also divided as: G1 (17-20 years old), G2 (21-24 years old), G3 (25-28 years old), G4 (29-32 years old) and G5 (33 years old or more). The results indicate a moderate effect of age (F(4545)=8.197; p<0.001; η2=0.057) and a small effect of playing position (F(4545)=2.993; p<0.05; η2=0.021) on torque of concentric extensors; mainly from midfielders and goalkeepers with 29 years or more. Soccer players from different field positions are subjected to different ageing related effects on their muscular performance during their career special attention should be given to these players to avoid reduction in physical performance



#3 Effects of regular exercise on inflammatory biomarkers and lipid parameters in soccer players

Reference: J Immunoassay Immunochem. 2021 Mar 22;1-11.  doi: 10.1080/15321819.2021.1898421. 

Authors: Abdulmecit Afşin, Eren Bozyılan, Ramazan Asoğlu, Yusuf Hoşoğlu, Aykut Dündar

Summary: Since chronic dyslipidemia and inflammation play a major role in the etiopathogenesis of atherosclerotic plaque, we investigated the effects of a 7-week exercise on the serum lipid profile, plasma atherogenic index (PAI), and inflammatory biomarkers interleukin (IL), tumor necrosis factor (TNF)-α, and monocyte chemoattractant protein (MCP)-1 in male soccer players. Methods: The participants in this study were 22 healthy male soccer players aged 19-25 years. IL-1β, IL-6, IL-10, TNF-a, MCP-1, and lipid profile were recorded before and after the program. PAI was calculated as log (TG/HDL-C), where TG is triglyceride and HDL-C is high-density lipoprotein cholesterol. Results: There were significant decreases in post-exercise IL-6, TNF-α, and MCP-1 (for all, p< .05). Compared to the pretest values, there were significant decreases in posttest total cholesterol (TC), TGs, low-density lipoprotein (LDL), non- high-density lipoprotein cholesterol (non-HDL-C), and PAI (for all, p< .05). In contrast, HDL-C values increased after exercise (p< .001). After exercise training TC, TGs, LDL-C, non-HDL-C, and PAI decreased and HDL-C increased, indicating improvement in parameters of dyslipidemia. The decreases in IL-6, TNF-α, and MCP-1 suggest a decrease in systemic inflammation.



#4 Assessment of skeletal age in youth female soccer players: Agreement between Greulich-Pyle and Fels protocols

Reference: Am J Hum Biol. 2021 Mar 21;e23591.  doi: 10.1002/ajhb.23591.

Authors: Diogo V Martinho, Manuel J Coelho-E-Silva, João Valente-Dos-Santos, Cláudia Minderico, Tomás G Oliveira, Inês Rodrigues, Jorge Conde, Lauren B Sherar, Robert M Malina

Summary: The purpose of the study was to evaluate the agreement between the Fels and Greulich-Pyle methods for the assessment of skeletal age (SA) in female youth soccer players. The sample included 441 Portuguese players 10.08-16.73 years of age who regularly participated in organized and competitive soccer. Standardized radiographs of the left hand-wrist were obtained and analyzed by an experienced examiner. SA was estimated with the Fels and Greulich-Pyle (GP) methods. Differences between SA and chronological age (CA) were used to define skeletal maturity groups: late, average and early maturing. In addition to descriptive statistics, Cohen's kappa and Lin concordance correlation coefficients were used to evaluate agreement between methods. Intraindividual differences in SA based on the two methods varied between 0.10 to 1.47 years among age groups with larger mean differences at older ages. Agreement of maturity classifications between methods was 74% at younger ages (under-13: kappa = 0.48; under-14: kappa = 0.39; Lin CCC = 0.68) and declined with increasing CA (under-17: 19% agreement; kappa = 0.001; Lin CCC = 0.11). About 19% of the total sample was skeletally mature with the Fels method and an SA was not assigned; in contrast, no players were skeletally mature with the GP method.

GP SAs were systematically lower than Fels SAs among female soccer players. Intraindividual variability in SAs between methods was considerable. The findings highlight the impact of method on estimates of maturity status.



#5 Leveling the Playing Field: A New Proposed Method to Address Relative Age- and Maturity-Related Bias in Soccer

Reference: Front Sports Act Living. 2021 Mar 4;3:635379. doi: 10.3389/fspor.2021.635379. eCollection 2021.

Authors: Werner F Helsen, Martine Thomis, Janet L Starkes, Sander Vrijens, Gerrit Ooms, Calum MacMaster, Chris Towlson

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Summary: Despite various solutions proposed to solve the relative age effect (RAE), it is still a major problem confounding talent identification and selection processes. In the first phase, we sampled 302 under 7-21 academy soccer players from two Belgian professional soccer clubs to explore the potential of a new approach to solve the inequalities resulting from relative age- and maturity-related bias. This approach allocates players into four discrete quartile groups based on the midway point of their chronological and estimated developmental (ED) birth dates (calculated using the growth curves for stature of Belgian youth). With the use of chi square analyses, a RAE was found (p < 0.01) for the overall sample (Q1 = 41.4% vs. Q4 = 14.9%) that completely disappeared after reallocation (Q1 = 26.5%; Q2 = 21.9%; Q3 = 27.5%; Q4 = 24.2%). According to the new allocation method, the stature difference was reduced, on average, by 11.6 cm (from 24.0 ± 9.9 to 12.4 ± 3.4 cm, d = 1.57). Body mass difference between the two methods was 1.9 kg (20.1 ± 11.3-18.2 ± 13.1 kg, respectively, d = 0.15). The new method created a maximum chronological age difference of 1.9 vs. 0.8 years for the current method. With the use of this method, 47% of the players would be reallocated. Twenty-three percent would be moved up one age category, and 21% would be moved down. In the second phase, we also examined 80 UK academy soccer players to explore if reallocating players reduces the within-playing group variation of somatic and physical fitness characteristics. The percentage coefficient of variation (%CV) was reduced (0.2-10.1%) in 15 out of 20 metrics across U11-U16 age categories, with the U13 age category demonstrating the largest reductions (0.9-10.1%) in CV. The U12 and U13 age categories and associated reallocation groupings showed trivial to small (ES = 0.0-0.5) between-method differences and trivial to moderate (ES = 0.0-1.1) differences within the U14-U16 age categories. A reduction in RAE may lead to fewer dropouts and thus a larger player pool, which benefits, in turn, talent identification, selection, and development.



#6 Motor performance is not related to injury risk in growing elite-level male youth football players. A causal inference approach to injury risk assessment

Reference: J Sci Med Sport. 2021 Mar 16;S1440-2440(21)00056-6. doi: 10.1016/j.jsams.2021.03.004.

Authors: Nikki Rommers, Roland Rössler, Ian Shrier, Matthieu Lenoir, Erik Witvrouw, Eva D'Hondt, Evert Verhagen

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Summary: The aim was to identify the causal relation between growth velocity and injury in elite-level youth football players, and to assess the mediating effects of motor performance in this causal pathway. We measured the body height of 378 male elite-level football players of the U13 to U15 age categories three to four months before and at the start of the competitive season. At the start of the season, players also performed a motor performance test battery, including motor coordination (Körperkoordinationstest für Kinder), muscular performance (standing broad jump, counter movement jump), flexibility (sit and reach), and endurance measures (YoYo intermittent recovery test). Injuries were continuously registered by the academies' medical staff during the first two months of the season. Based on the causal directed acyclic graph (DAG) that identified our assumptions about causal relations between growth velocity (standardized to cm/y), injuries, and motor performance, the causal effect of growth velocity on injury was obtained by conditioning on maturity offset. We determined the natural indirect effects of growth velocity on injury mediated through motor performance. In total, 105 players sustained an injury. Odds ratios (OR) showed a 15% increase in injury risk per centimetre/year of growth velocity (1.15, 95%CI: 1.05-1.26). There was no causal effect of growth on injury through the motor performance mediated pathways (all ORs were close to 1.0 with narrow 95%CIs). Growth velocity is causally related to injury risk in elite-level youth football players, but motor performance does not mediate this relation.



#7 Space evaluation in football games via field weighting based on tracking data

Reference: Sci Rep. 2021 Mar 9;11(1):5509. doi: 10.1038/s41598-021-84939-7.

Authors: Takuma Narizuka, Yoshihiro Yamazaki, Kenta Takizawa

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Summary: In football game analysis, space evaluation is an important issue because it is directly related to the quality of ball passing or player formations. Previous studies have primarily focused on a field division approach wherein a field is divided into dominant regions in which a certain player can arrive prior to any other players. However, the field division approach is oversimplified because all locations within a region are regarded as uniform herein. The objective of the current study is to propose a fundamental framework for space evaluation based on field weighting. In particular, we employed the motion model and calculated a minimum arrival time [Formula: see text] for each player to all locations on the football field. Our main contribution is that two variables [Formula: see text] and [Formula: see text] corresponding to the minimum arrival time for offense and defense teams are considered; using [Formula: see text] and [Formula: see text], new orthogonal variables [Formula: see text] and [Formula: see text] are defined. In particular, based on real datasets comprising of data from 45 football games of the J1 League in 2018, we provide a detailed characterization of [Formula: see text] and [Formula: see text] in terms of ball passing. By using our method, we found that [Formula: see text] and [Formula: see text] represent the degree of safety for a pass made to [Formula: see text] at t and degree of sparsity of [Formula: see text] at t, respectively; the success probability of passes could be well-fitted using a sigmoid function. Moreover, a new type of field division approach and evaluation of ball passing just before shots using real game data are discussed.



#8 Physical performance and loading for six playing positions in elite female football: full-game, end-game, and peak periods

Reference: Scand J Med Sci Sports. 2021 Mar 22. doi: 10.1111/sms.13877. 

Authors: Jeppe Panduro, Georgios Ermidis, Line Røddik, Jeppe F Vigh-Larsen, Esben Elholm Madsen, Malte Nejst Larsen, Svein Arne Pettersen, Peter Krustrup, Morten B Randers

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Summary: The present study investigated the position-specific match demands and heart rate response of female elite footballers, with special focus on the full-game, end-game, and peak-intensity periods. In total, 217 match observations were performed in 94 players from all eight teams of the best Danish Women's League, that is, goalkeepers (GK, n = 10), central defenders (CD, n = 23), full-backs (FB, n = 18), central midfielders (CM, n = 28), external midfielders (EM, n = 18), and forwards (FW, n = 11). Positional data (GPS; 10 Hz Polar Team Pro) and HR responses were collected. HRmean and HRpeak were 87%-89% and 98%-99% of HRmax , for outfield players, with no positional differences. CM, EM, and FB covered 8%-14% greater (P < .001) match distances than CD. EM, FW, FB, and CM performed 40%-64% more (P < .05) high-speed running and 41%-95% more (P < .01) very-high-speed running (VHSR) than CD. From the first to the last 15-minute period, total distance, except for FW, number of VHSR, except FB, peak speed and sum of accelerations and sum of decelerations decreased (P < .05) for all outfield positions. In the most intense 5-minute period, EM, FB, and CM performed 25%-34% more (P < .01) HSR than CD, whereas EM, FW, and FB performed 36%-49% more (P < .01) VHSR than CD. In conclusion, competitive elite female matches impose high physical demands on all outfield playing positions, with high aerobic loading throughout matches and marked declines in high-speed running and intense accelerations and decelerations toward the end of games. Overall physical match demands are much lower for central defenders than for the other outfield playing positions, albeit this difference is minimized in peak-intensity periods.



#9 Brain Activation During the Observation of Real Soccer Game Situations Predict Creative Goalscoring

Reference: Soc Cogn Affect Neurosci. 2021 Mar 24;nsab035. doi: 10.1093/scan/nsab035. Online ahead of print.

Authors: Christian Rominger, Karl Koschutnig, Daniel Memmert, Ilona Papousek, Corinna M Perchtold-Stefan, Mathias Benedek, Andreas R Schwerdtfeger, Andreas Fink

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Summary: Creativity is an important source of success in soccer players. In order to be effective in soccer, unpredictable, sudden and at the same time creative (i.e., unique, original, and effective) ideas are required in situations with high time pressure. Accordingly, creative task performance in soccer should be primarily driven by rapid and automatic cognitive processes. This study investigated if functional patterns of brain activation during the observation/encoding of real soccer game situations can predict creative soccer task performance. A machine learning approach (multivariate pattern recognition) was applied in a sample of 35 experienced male soccer players. Results revealed that brain activation during the observation of the soccer scenes significantly predicted creative soccer task performance, while brain activation during the subsequent ideation/elaboration period did not. The identified brain network included areas such as the angular gyrus, the supramarginal gyrus, the occipital cortex, parts of the cerebellum and (left) supplementary motor areas, which are important for semantic information processing, memory retrieval, integration of sensory information, and motor-control. This finding suggests that early and presumably automatized neurocognitive processes, such as (implicit) knowledge about motor movements, and the rapid integration of information from different sources are important for creative task performance in soccer.



#10 Optimal Pretaper Phase on Physical Match Performance in Professional Soccer

Reference: Int J Sports Physiol Perform. 2021 Mar 23;1-7.  doi: 10.1123/ijspp.2020-0334. Online ahead of print.

Authors: Wassim Moalla, Mohamed Saifeddin Fessi, Sabeur Nouira, Alberto Mendez-Villanueva, Valter Di Salvo, Said Ahmaidi

Summary: The purpose was to investigate the optimal pretaper duration on match running performance in a professional soccer team. The training load was monitored during daily training sessions and matches during 2 seasons according to different periodization strategies. Matches' running distances were collected using match analysis system. The data were analyzed in 3 types of mesocycle blocks of 5 (M5), 4 (M4), and 3 weeks (M3), concludes all of them by 1 taper week. Significant decreases in the training load during the taper weeks compared to standard weeks were observed in 3 types of mesocycle blocks (d ≥ 5; P < .01). An increase in overall match running performance was observed in matches played after the taper weeks compared to matches played after the standard weeks during M4 for all speed ranges (d ≥ 1.3; P < .05). The increase was only observed in low-intensity running (d = 1.3; P < .04) and total distance, low-intensity running, and intense running (d ≥ 1.3; P < .05) in M5 and M3, respectively. Match running performance following the taper weeks between the 3 different mesocycle durations was significantly higher in M4 for the number of high-speed running, sprinting, and high-intensity running (P < .05). The greatest enhancement of match running performance was observed at M4 when the training load was decreased by approximately 18% during the tapering period. This study suggests that a period of 3 standard weeks of training followed by 1 taper week is the optimal taper strategy when compared to different pretaper durations.



#11 Eyes-Open Versus Eyes-Closed Somatosensory Motor Balance in Professional Soccer Players With Chronic Ankle Instability: A Case-Control Study

Reference: Orthop J Sports Med. 2021 Mar 8;9(3):2325967120983606. doi: 10.1177/2325967120983606. eCollection 2021 Mar.

Authors: David Rodríguez-Sanz, Antonio García-Sánchez, Ricardo Becerro-de-Bengoa-Vallejo, Eva María Martínez-Jiménez, César Calvo-Lobo, Josué Fernández-Carnero, Marta Elena Losa-Iglesias, Daniel López-López

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Summary: Chronic ankle instability (CAI) is a condition defined by certain structural and functional deficits in the ankle joint complex after acute ankle injury. These deficits include pathological joint laxity, impaired postural control, and decreased strength and neuromuscular control. The purpose was to compare an eyes-open versus an eyes-closed balance training protocol in professional soccer players with CAI. For this study, we evaluated 19 players from 2 professional soccer teams in Madrid, Spain, all of whom had CAI. Participants from both teams were randomly assigned to an eyes-open group (n = 9) or eyes-closed group (n = 10). All participants completed 4 weeks of a supervised exercise protocol consisting of 3 sessions per week. Members of both the eyes-open and eyes-closed groups performed the same exercise protocol in the same order of execution. At the end of the protocol, the participants were assessed for pain (visual analog scale), ankle dorsiflexion range of motion (weightbearing lunge test), dynamic stability (Star Excursion Balance Test), and fear of movement and reinjury (Tampa Scale for Kinesiophobia). We compared results both before and after balance training and between the eyes-open and eyes-closed balance training groups. Statistically significant differences were found for all of the assessed variables before and after balance training. No statistically significant differences were found between the eyes-closed and eyes-open groups on any variable. In the current study, eyes-closed balance training was not more effective than eyes-open balance training for CAI in professional soccer players.



#12 Quantification of training and match load in elite youth soccer players: a full-season study

Reference: J Sports Med Phys Fitness. 2021 Mar 26. doi: 10.23736/S0022-4707.21.12236-4. Online ahead of print.

Authors: Hadi Nobari, Amir Barjaste, Hamed Haghighi, Filipe M Clemente, Jorge Carlos-Vivas, Jorge Perez-Gomez

Summary: The present study aimed to quantify training and match load in elite young soccer players over the course of an entire season. Using a longitudinal design, session-rate of perceived exertion (s-RPE) and its metrics [weekly acute workload (wAW), acute to chronic workload ratio (wACWR), training monotony and training strain] were examined in twenty-one elite young soccer players (mean±standard deviation; age, 16.1±0.2 years; height, 176.8±5.6 cm; body mass, 67.3±5.7 kg; BMI, 21.5±1.4 kg/m2; VO2max, 47.6±3.8 during the whole season containing 4 meso-cycles: Pre-season (Pre-S), Earlyseason (Ear-S), Mid-season (Mid-S), and End-season (End-S). Repeated-measures analysis of variance examined variations in s-RPE load data across the 4 meso-cycles and 1-week of micro-cycle. Analyzing data revealed the End-S had a significant greater wAW compared to Early-S (p = 0.002, g = 0.96) and Mid-S (p < 0.001, g = 1.09). However, no differences between in-season periods were observed in wACWR (p = 0.524). The within-week variations revealed significant lower wAW in pre-match a day (MD-1) (p < 0.001), 1 day after match (MD+1) (p < 0.001) and 2 days after match (MD+2) (p < 0.001) compared to match day (MD) for overall team analysis. Additionally, analyses by playing position showed that fullbacks have a significant lower AW in MD+2 compared to MD (p < 0.029). The periodization of training load indicated variations across the whole season in young elite players. The weekly micro-cycle perceived load could be identified as follows; there are higher training loads on MD-3 and MD-2 which was similar to intensities experienced by players throughout the match play and, furthermore, lower overall WL on the MD+1 and MD+2 in order to ensure the optimal recovery of the players.



#13 Trends in Soccer-Related Ocular Injuries within the United States from 2010 through 2019

Reference: Semin Ophthalmol. 2021 Mar 30;1-6.  doi: 10.1080/08820538.2021.1909077. Online ahead of print.

Authors: Parth A Patel, Rhea Gopali, Anvith Reddy, Kajol K Patel

Summary: Soccer participation within the United States continues to increase, necessitating consideration of the various injuries that may occur. The present study analyzes trends in the incidence of ocular injuries secondary to soccer trauma, the associated mechanism, and related visual sequelae, and quantifies age- and sex-specific differences in the distributions of these variables. The Consumer Product Safety Commission's National Electronic Injury Surveillance System (NEISS) was queried for soccer-related ocular injuries from 2010 through 2019. Data exclusively focused on the globe were selected, and information regarding age, sex, specific diagnosis, mechanism of injury, and visual sequelae were acquired. Significance was calculated using the chi-squared test. 628 NEISS entries were evaluated, extrapolating to a national average incidence of approximately 1580 soccer-related ocular injuries per year. There were a relatively static number of events during the ten-year time period of study. The most common diagnoses were contusions or abrasions (36.1%); among records with a reported mechanism of injury, the most common was contact with the soccer ball (80.9%). Visual sequelae were noted in a significant minority of patients (15.4%). Patients ≤18 and males comprised the majority of visits (68.2% and 70.2%, respectively). Significant sex- and age-specific differences were observed in the distributions of diagnoses. There are serious visual consequences associated with soccer-related ocular injury. Despite the existence of eye protection, there remain no regulations requiring its consistent use. Therefore, among all parties involved (e.g., players, families, and physicians), there remains a need to increase education regarding the potential ocular dangers associated with the sport.



#14 Exploring Relationships Between Anthropometry, Body Composition, Maturation, and Selection for Competition: A Study in Youth Soccer Players

Reference: Front Physiol. 2021 Mar 11;12:651735. doi: 10.3389/fphys.2021.651735. eCollection 2021.

Authors: Filipe Manuel Clemente, Cain C T Clark, César Leão, Ana Filipa Silva, Ricardo Lima, Hugo Sarmento, António J Figueiredo, Thomas Rosemann, Beat Knechtle

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Summary: The purpose of this study was to analyze variations of selection for competition between late and early mature players and test the relationships between anthropometry, body composition, maturation, and selection for competition. Seventy-nine youth soccer players from under-11 to under-14 participated in this study, over 6 months. Body composition and maturity offset were estimated based on anthropometric data collected. Participants were also monitored for their number of matches as starters and time of play accrued in minutes. Minutes played had large correlation coefficients with maturity offset (r = 0.58), and leg length and sitting height interaction (r = 0.56). Multiple linear regression explained 35% of the variation in minutes played (p < 0.001, R 2 = 0.41, R 2 adjusted = 0.35, RMSE = 334.8), but only 12% of the variation in matches as starter (p = 0.04, R 2 = 0.21, R 2 adjusted = 0.12, RMSE = 5.47) between above and below the median of the maturity offset was accounted for, respectively. Although maturation may play a role in the minutes of play accrued and matches as starters in young, it is not necessarily determining. A significant amount of the variation in the minutes of play accrued of players can be accounted for when considering body composition and anthropometric data.



#15 One year of Football Fitness improves L1-L4 BMD, postural balance and muscle strength in women treated for breast cancer

Reference: Scand J Med Sci Sports. 2021 Apr 1.  doi: 10.1111/sms.13963.

Authors: Jacob Uth, Bjørn Fristrup, Victor Sørensen, Eva Wulff Helge, Maja Kjaergaard Christensen, Julie Boye Kjaergaard, Trine Kjeldgaard Møller, Jørn Wulff Helge, Niklas Rye Jørgensen , Mikael Rørth, Eva Soelberg Vadstrup, Peter Krustrup 

Summary: The purpose was to examine efficacy of 12 months Football Fitness offered twice per week on bone mineral density (BMD), bone turnover markers (BTM), postural balance, muscle strength and body composition in women treated for early-stage breast cancer (BC). Women treated for early-stage BC were randomised to Football Fitness (FFG, n=46) or control (CON, n=22) in a 2:1 ratio for 12 months, with assessments performed at baseline, 6 months and 12 months. Outcomes were total body-, lumbar spine- and proximal femur BMD, total body lean and fat mass, leg muscle strength, postural balance, and plasma amino-terminal propeptide of type 1 procollagen (P1NP), osteocalcin and C-terminal telopeptide of type 1 collagen (CTX). Intention-to-treat (ITT) analyses and per-protocol analyses (≥50% attendance in FFG) were performed using linear mixed models. Participants in FFG completing the 12-month intervention (n=33) attended 0.8 (SD=0.4) sessions per week. Intention to treat analysis of mean changes over 12 months showed significant differences in L1-L4 BMD (0.029 g/cm2 , 95%CI: 0.001 to 0.057), leg press strength (7.2 kg, 95%CI: 0.1 to 14.3) and postural balance (-4.3 n need of support, 95%CI: -8.0 to -0.7) favouring FFG compared to CON. In the per-protocol analyses, L1-L4 and trochanter major BMD were improved (p=0.012 and 0.030, respectively) in FFG compared to CON. No differences were observed between groups in BTMs in the ITT or per protocol analyses. One year of Football Fitness training may improve L1-L4 BMD, leg muscle strength and postural balance in women treated for early-stage breast cancer.






Low Horizontal Force Production Capacity during Sprinting as a Potential Risk Factor of Hamstring Injury in Football

Clear decreases in horizontal force production capacity during sprint acceleration have been reported after hamstring injuries (HI) in football players. We aimed to analyze the association between sprint running horizontal force production capacities at low (FH0) and high (V0) velocities and HI occurrence in football.





An Examination of the Relationship Between Coaches’ Transformational Leadership and Athletes’ Personal and Group Characteristics in Elite Youth Soccer

The purpose of the study was to examine the relationship between elite youth athletes’ perceptions of coaches’ transformational coaching-behaviours and variables linked to transformational leadership in other settings (i.e., group cohesion, motivational climate, self-regulation of learning and athlete satisfaction.





Latest research in football - week 24 - 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 Maximal Strength, Sprint, and Jump Performance in High-Level Female Football Players Are Maintained With a Customized Training Program During the COVID-19 Lockdown

Reference: Front Physiol. 2021 Feb 26;12:623885.  doi: 10.3389/fphys.2021.623885. eCollection 2021.

Authors: Sigurd Pedersen, Dag Johansen, Andrea Casolo, Morten B Randers, Edvard H Sagelv, Boye Welde, Andreas Kjæreng Winther, Svein Arne Pettersen

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Summary: The COVID-19 outbreak with partial lockdown has inevitably led to an alteration in training routines for football players worldwide. Thus, coaches had to face with the novel challenge of minimizing the potential decline in fitness during this period of training disruption. In this observational pre- to posttest study involving Norwegian female football players (18.8 ± 1.9 years, height 1.68 ± 0.4 m, mass 61.3 ± 3.7 kg), we investigated the effects of a prescribed home-based and group-based intervention, implemented during the COVID-19 lockdown, on maximal muscular force production and high velocity variables. Specifically, maximal partial squat strength one repetition maximum (1RM), counter movement jump (CMJ) and 15 m sprint time were assessed 1 week prior to the lockdown and 12 weeks after the onset of lockdown. We also collected training content and volume from the prescribed training program and self-reported perceived training quality and motivation toward training. We observed no change in 1RM [pretest: 104 ± 12 kg, posttest: 101 ± 11 kg (P = 0.28)], CMJ height [pretest: 28.1 ± 2.3 cm, posttest: 26.8 ± 1.9 (P = 0.09)], and 15 m sprint time [pretest: 2.60 ± 0.08 s, posttest: 2.61 ± 0.07 s (P = 0.52)]. Our findings suggest that a prescribed home-based and group-based intervention with increased training time devoted to strength, jump, and sprint ability, and regulated to obtain a sufficient infection control level is feasible and effective to preserve strength, jumping, and sprinting abilities of high-level female football players during a ∼ 3-month period of a pandemic-induced lockdown.



#2 Mapping default mode connectivity alterations following a single season of subconcussive impact exposure in youth football

Reference: Hum Brain Mapp. 2021 Mar 18. doi: 10.1002/hbm.25384.

Authors: Jesse C DeSimone, Elizabeth M Davenport, Jillian Urban, Yin Xi, James M Holcomb, Mireille E Kelley, Christopher T Whitlow, Alexander K Powers, Joel D Stitzel, Joseph A Maldjian

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Summary: Repetitive head impact (RHI) exposure in collision sports may contribute to adverse neurological outcomes in former players. In contrast to a concussion, or mild traumatic brain injury, "subconcussive" RHIs represent a more frequent and asymptomatic form of exposure. The neural network-level signatures characterizing subconcussive RHIs in youth collision-sport cohorts such as American Football are not known. Here, we used resting-state functional MRI to examine default mode network (DMN) functional connectivity (FC) following a single football season in youth players (n = 50, ages 8-14) without concussion. Football players demonstrated reduced FC across widespread DMN regions compared with non-collision sport controls at postseason but not preseason. In a subsample from the original cohort (n = 17), players revealed a negative change in FC between preseason and postseason and a positive and compensatory change in FC during the offseason across the majority of DMN regions. Lastly, significant FC changes, including between preseason and postseason and between in- and off-season, were specific to players at the upper end of the head impact frequency distribution. These findings represent initial evidence of network-level FC abnormalities following repetitive, non-concussive RHIs in youth football. Furthermore, the number of subconcussive RHIs proved to be a key factor influencing DMN FC.



#3 A ninety-minute football match increases hamstring flexibility in professional players

Reference: J Biol Regul Homeost Agents. Sep-Oct 2020;34(5 Suppl. 1):87-92. IORS Special Issue on Orthopedics.

Authors: G Kakavas, N Malliaropoulos, A Kaliakmanis, B Georgios, N Maffulli

Summary: Flexibility is an integral component in any conditioning program. Flexibility has been defined as the ability of a muscle to lengthen and allow one or more joints in a kinetic chain to move through a range of motion. The lack of flexibility of the hamstring muscle group has been associated with a higher risk of non-contact muscle injury, and for several other conditions, such as changes in lumbopelvic rhythm, greater thoracic kyphosis and lumbar flexion, and lower back pain. The present study explored the effects of a 90-minute soccer match on hamstring group flexibility. Our study shows that a 90-minute football match favorably impacts the flexibility of the hamstring muscle group. Flexibility is a modifiable risk factor for muscle strain injury. It remains to be ascertained how long this effect lasts, and whether it may be associated with the risk of developing or avoiding noncontact injury to the hamstring muscle group.



#4 Epidemiological analysis of injury occurrence and current prevention strategies on international amateur football level during the UEFA Regions Cup 2019

Reference: Arch Orthop Trauma Surg. 2021 Mar 19. doi: 10.1007/s00402-021-03861-9.

Authors: Dominik Szymski, Volker Krutsch, Leonard Achenbach, Stephan Gerling, Christian Pfeifer, Volker Alt, Werner Krutsch, Oliver Loose

Summary: Football is the most popular sport worldwide and results in a high frequency of injuries. So far, mainly injuries in professional football have been investigated, and the literature lacks data regarding detailed injury epidemiology and current prevention data in amateur football tournaments. A prospective cohort study investigated an international amateur football tournament, the UEFA Regions' Cup, which took place in 2019 in Germany. Injury epidemiology, current prevention strategies of the teams and the implementation of the UEFA concussion protocol were investigated in detail by means of standardized injury definitions and data samples for football (Fuller et al., Scand J Med Sci Sports 16:83-92, , 2006). 138 player of 8 teams participated in this study, while 39 players were excluded. Overall injury incidence was 12.5 per 1000 h total football exposure, 43.5 per 1000 h for match exposure. No injuries were registered during training. Injury prevalence was 14.1% per player and 1.1 injuries per match were registered. The lower extremity was predominantly affected by injuries (71.4%) and the majority of injuries (78.6%) were non-severe injury types like contusions (50%) and sprains (18.2%). Two head injuries, one contusion and one skin lesion, were handled by the guidelines of the UEFA concussion protocol. 44.4% of the players indicated at least one previous injury before tournament, 45.3% of them during the last two football seasons before start of the tournament. Injury prevention performance was included in all participating teams during the tournament by warm up or training strategies (100%). During the warm-up program just 5 exercises of the FIFA 11 + program was detected by this investigation in participating teams to be done by more half of the teams. Running exercises were the most frequently performed exercises, while trunk muscle exercises were less represented (14.3%). This study presents for the first time epidemiological injury and prevention data of the UEFA Regions Cup. Injury incidence was higher compared to injury reports of regular seasons, but lower compared to other amateur football tournaments. Currently used prevention programs revealed trunk muscle exercises as often neglected.



#5 Long-Term Patterns of Bone Mineral Density in an Elite Soccer Player

Reference: Front Physiol. 2021 Feb 25;12:631543.  doi:10.3389/fphys.2021.631543. eCollection 2021.

Authors: Chiara Milanese, Valentina Cavedon, Giuliano Corradini, Aiace Rusciano, Carlo Zancanaro

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Summary: Changes in bone mineral density (BMD) have been associated with association football (soccer) participation. Seasonal changes in BMD of soccer players have been proposed as well. However, previous investigations were based on short-term observations. Actually, longitudinal investigation of BMD in soccer players is lacking, possibly because of frequent inter-club transfer, changes in club policy or continued availability of the relevant facilities. Dual-energy X-ray Absorptiometry (DXA)-measured areal BMD (aBMD) was obtained during the competitive season in an elite soccer player along 10 consecutive years. Findings showed that (1) aBMD tends to increase with age, independently of body mass; (2) The right (preferred, kicking) leg has higher aBMD than the left (non-preferred, support) one; (3) Meaningful (i.e., >least significant change, LSC) changes in aBMD take place along the season; and (4) The off-season (transition) period has no effect on aBMD. Findings prompt for future research aimed at clarifying the long-term and seasonal patterns of bone characteristics in soccer in relation with age and type/dose of training. Season-around, long-term scrutiny of bone status in soccer players would help controlling for possible changes/asymmetries in bone mineralization/strength.



#6 Head Impact Situations in Professional Football (Soccer)

Reference: Sports Med Int Open. 2021 Mar 10;5(2):E37-E44. doi: 10.1055/a-1338-1402. eCollection 2021 Mar.

Authors: Florian Beaudouin, Daniel Demmerle, Christoph Fuhr, Tobias Tröß, Tim Meyer

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Summary: The aim was to assess head impact incidents (HIIs) and to distinguish diagnosed head injuries from other incidents, a video observation analysis of match HIIs was conducted in the German Bundesliga (2017/18 season). Video recordings of each match were screened to identify the respective events. Head injury data were identified by a prospective injury registry. HII and head injury incidence rates (IR) were calculated with 95% CIs. The total number of HIIs was 1,362 corresponding to an IR of 134.9/1000 match hours (95% CI 127.9–142.2). In 123 HII (IR 12.2, 95% CI 10.2–14.5) the contact was classified as severe. Head contact with the opponent was the most frequent cause (85%). The most frequent mechanism was in 44% (combined) the arm and elbow-to-head, followed by head-to-head and hand-to-head contacts (each 13%). In 58%, the HIIs occurred during header duels. Twenty-nine head injuries were recorded (IR 2.9, 95% CI 2.0–4.1). Concussions/traumatic brain injuries accounted for 48%, head/facial fractures 24%, head/facial contusions 21%, and lacerations/abrasions 7%. The number of HIIs not classified as concussions/more severe trauma was high. Identification of HIIs and head injury severity should be improved during on-field assessment as many head injuries might go unrecognised based on the large number of HIIs.



#7 Musculoskeletal Injuries and Their Association With Previous Concussion History: A Prospective Study of High School Volleyball and Soccer Players

Reference: Am J Sports Med. 2021 Mar 15;363546521997116.  doi: 10.1177/0363546521997116. 

Authors: Kevin M Biese, Stephanie A Kliethermes, Andrew M Watson, Timothy A McGuine, Pamela J Lang, David R Bell, M Alison Brooks

Summary: Sports-related concussions may have a neurobiological recovery period that exceeds the period of clinical recovery, and one consequence of an extended neurobiological recovery may be the risk of subsequent musculoskeletal injuries. Most literature citing an increased risk of musculoskeletal injury after a sports-related concussion has been reported in populations other than adolescent athletes. The purpose was to prospectively determine if incidence rates of musculoskeletal injury differ between adolescent athletes with and without a previous sports-related concussion, while controlling for sex, sport, and age. A secondary aim was to determine if this relationship differs between male and female athletes of the same sport. Our hypotheses were that acute-noncontact injury rates would be higher in athletes with a previous sports-related concussion when compared with athletes without a previous sports-related concussion, and that this relationship would exist only in female athletes and not male athletes. High school soccer and volleyball players were recruited in 2 prospective cohort studies that observed 4837 athletes during their sporting season (females, 80%; soccer, 57%; mean [SD] age, 15.6 [1.1] years). At preseason, all participants self-reported demographics and previous sports-related concussion within the past 12 months. During the sport season, team athletic trainers electronically recorded athlete exposures and injury data, including injury characteristics. Injury rates per 1000 athlete exposures and injury rate ratios (IRRs) with 95% confidence intervals were calculated. All injury rates and IRRs were adjusted for sex, age, and sport.

Results: The rate of acute-noncontact lower extremity injury was 87% greater (IRR, 1.87; 95% CI, 1.29-2.74) in participants with a previous sports-related concussion versus those without one. The acute-noncontact lower extremity injury rates (IRRs) for females and males with a previous sports-related concussion were 1.76 (95% CI, 1.19-2.59) and 2.83 (95% CI, 0.85-9.50), respectively. No difference was detected in acute-contact (IRR, 0.98; 95% CI, 0.56-1.73) or overuse (IRR, 1.09; 95% CI, 0.51-2.37) lower extremity injury rates by previous sports-related concussion. Female adolescent athletes who reported a sports-related concussion within the past 12 months were more likely to sustain an acute-noncontact lower extremity injury during their high school sports season when compared with female athletes without a previous sport-related concussion.



#8 External and internal load during Small-Sided Games in soccer: use or not floaters

Reference: J Sports Med Phys Fitness. 2021 Mar 15.  doi: 10.23736/S0022-4707.21.12103-6. Online ahead of print.

Authors: Jose A Asian-Clemente, Alberto Rabano-MuÑoz, Francisco J NuÑez, Luis Suarez-Arrones

Summary: The purpose of the present study was to analyse the internal and external loads on regular and floater players during standardized small-sided games (SSGs) with different numbers of players (teams of 3, 5, or 7 players). Fifteen male semi-professional football players played different SSGs maintaining the same relative area per player. Total distance (TD), distance covered at different speeds (DC), the number of accelerations and decelerations, maximal (HRmax) and mean (HRmean) heart rate and rate of perceived exertion (RPE) were registered. Regular players showed greater internal and external loads in SSGs with 3 and 5 players without floaters than with floaters (ES 0.60-to-1.27). Likewise, with floaters, regular players in the SSGs with 3 performed more accelerations (ES 1.40 and 1.17) and with 7 achieved higher TD, DC > 14 km·h-1, HRmax and HRmean (ES 0.66-to-2.79) than any other. During SSGs with 7 players the floaters showed a higher TD and decelerations than in other SSGs (ES 0.47-to-1.70), and a higher DC (0-6.9 km·h-1,14-17.9 km·h-1) and RPE than in SSGs with 3 players (ES 0.59-to-0.89). During SSGs with 5, the floaters showed a higher TD, HRmax, HRmean and RPE than in SSGs with 3 (ES 0.86-to-1.45). In all SSGs, regular players showed higher TD, DC (14-17.9 km·h-1), accelerations, decelerations and HRmean than floaters (ES 1.24-to-6.23). Coaches must carefully design SSGs because the number of players and the presence or absence of floaters can affect the external-internal load expressed.



#9 Effect of whey vs. soy protein supplementation on recovery kinetics following speed endurance training in competitive male soccer players: a randomized controlled trial

Reference: J Int Soc Sports Nutr. 2021 Mar 16;18(1):23.  doi: 10.1186/s12970-021-00420-w.

Authors: Savvas Kritikos, Konstantinos Papanikolaou, Dimitrios Draganidis, Athanasios Poulios, Kalliopi Georgakouli, Panagiotis Tsimeas, Theofanis Tzatzakis, Dimitrios Batsilas, Alexios Batrakoulis, Chariklia K Deli, Athanasios Chatzinikolaou, Magni Mohr, Athanasios Z Jamurtas, Ioannis G Fatouros

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Summary: Soccer-specific speed-endurance training induces short-term neuromuscular fatigue and performance deterioration over a 72-h recovery period, associated with elevated markers of exercise-induced muscle damage. We compared the effects of whey vs. soy protein supplementation on field activity, performance, muscle damage and redox responses following speed-endurance training in soccer players. Ten well-trained, male soccer players completed three speed-endurance training trials, receiving whey protein (WP), soy protein (SP) or an isoenergetic placebo (PL; maltodextrin) according to a randomized, double-blind, crossover, repeated-measures design. A pre-loading period was applied in each trial during which protein supplementation was individually adjusted to reach a total protein intake of 1.5 g/kg/day, whereas in PL protein intake was adjusted at 0.8-1 g/kg/day. Following pre-loading, two speed-endurance training sessions (1 and 2) were performed 1 day apart, over a 3-day experimental period. During each session, field activity and heart rate were continuously monitored using global positioning system and heart rate monitors, respectively. Performance (isokinetic strength of knee extensors and flexors, maximal voluntary isometric contraction, speed, repeated sprint ability, countermovement jump), muscle damage (delayed-onset of muscle soreness, creatine kinase activity) and redox status (glutathione, total antioxidant capacity, protein carbonyls) were evaluated at baseline (pre), following pre-loading (post-load), and during recovery from speed-endurance training. High-intensity and high-speed running decreased (P ≤ 0.05) during speed-endurance training in all trials, but WP and SP mitigated this response. Isokinetic strength, maximal voluntary isometric contraction, 30-m speed, repeated sprint ability and countermovement jump performance were similarly deteriorated during recovery following speed-endurance training in all trials (P ≤ 0.05). 10 m speed was impaired at 24 h only in PL. Delayed-onset of muscle soreness, creatine kinase, total antioxidant capacity and protein carbonyls increased and glutathione decreased equally among trials following speed-endurance training (P ≤ 0.05), with SP inducing a faster recovery of protein carbonyls only at 48 h (P ≤ 0.05) compared to WP and PL. In conclusion, increasing daily protein intake to 1.5 g/kg through ingestion of either whey or soy protein supplements mitigates field performance deterioration during successive speed-endurance training sessions without affecting exercise-induced muscle damage and redox status markers.



#10 Coding Body Language in Sports: The Nonverbal Behavior Coding System for Soccer Penalties

Reference: J Sport Exerc Psychol. 2021 Mar 17;1-15.  doi: 10.1123/jsep.2020-0066. Online ahead of print.

Authors: Philip Furley, Alexander Roth

Summary: Nonverbal behavior (NVB) plays an important role in sports. However, it has been difficult to measure, as no coding schemes exist to objectively measure NVB in sports. Therefore, the authors adapted the Body Action and Posture Coding System to the context of soccer penalties, validated it, and initially used this system (Nonverbal Behavior Coding System for Soccer Penalties [NBCSP]) to explore NVB in penalties. Study 1 demonstrated that the NBCSP had good to excellent intercoder reliability regarding the occurrence and temporal precision of NVBs. It also showed that the coding system could differentiate certain postures and behaviors as a function of emotional valence (i.e., positive vs. negative emotional states). Study 2 identified differences in NVB for successful and missed shots in a sample of penalties (time spent looking toward the goal, toward the ground, right arm movement, and how upright the body posture was). The authors discuss the utility of the coding system for different sport contexts.



#11 Effects of Small-Sided Games vs. Running-Based High-Intensity Interval Training on Physical Performance in Soccer Players: A Meta-Analytical Comparison

Reference: Front Physiol. 2021 Mar 1;12:642703.  doi: 10.3389/fphys.2021.642703. eCollection 2021.

Authors: Filipe Manuel Clemente, Rodrigo Ramirez-Campillo, José Afonso, Hugo Sarmento

Summary: This systematic review with meta-analysis (SRMA) was conducted to compare the effects of SSG-based interventions vs. running-based HIIT interventions on soccer players' sprinting time (ST), vertical height jump (VJH), and change of direction time (CODt).  The data sources utilized were Web of Science, Scopus, SPORTDiscus, and PubMed. Results: An electronic search yielded 650 articles, six of which were included in the present study. Between-group analysis found a significant favoring effect of HIIT-based over SSG-based training interventions for the improvement of linear sprinting time (ES = 0.42; p = 0.012). A within-group analysis revealed a significant favoring effect of HIIT-based training interventions for improving linear sprinting time (ES = 0.42; p = 0.008) and CODt (ES = 1.04; p = 0.005) despite a non-significant effect on VJH (ES = 0.47; p = 0.22).  The meta-analytical comparison revealed favoring the effect of running-based HIIT over SSG-based interventions in sprinting performance, although no significant differences were observed for jumping and CODt performance. The findings suggest that SSG-based programs should be supplemented by other training methods that benefit determinant capacities in soccer players.



#12 The Risk of Knee Osteoarthritis in Professional Soccer Players

Reference: Dtsch Arztebl Int. 2021 Jan 29;118(4):49-55.  doi: 10.3238/arztebl.m2021.0007.

Authors: Alice Freiberg, Ulrich Bolm-Audorff, Andreas Seidler

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Summary: We address the question whether professional soccer players with and without macroinjury of the knee joint are at an elevated risk for knee osteoarthritis. A systematic review with meta-analyses was conducted. The study protocol was prospectively registered (registration number CRD42019137139). The MEDLINE, EMBASE, and Web of Science databases were searched for relevant publications; in addition, forward searching was performed, and the listed references were considered. All steps of the process were undertaken independently by two reviewers, and any discordances were resolved by consensus. For all publications whose full text was included, the methods used were critically evaluated. The quality of the evidence was judged using the GRADE criteria. The pooled odds ratio for objectively ascertained osteoarthrosis of the knee was 2.25 (95% confidence interval [1.41-3.61], I2 = 71%). When only radiologically ascertained knee osteoarthrosis was considered, the odds ratio was 3.98 [1.34; 11.83], I2 = 58%). The pooled risk estimator in studies in which knee joint macroinjury was excluded was 2.81 ([1.25; 6.32], I2 = 71%). A marked association was found between soccer playing and knee osteoarthritis in male professional soccer players. For female professional soccer players, the risk of knee osteoarthritis could not be assessed because of the lack of data. Knee injuries seem to play an important role in the development of knee osteoarthritis in professional soccer players.



#13 Effects of 12 weeks of recreational football (soccer) with caloric control on the glycemia and cardiovascular health of adolescent boys with type 1 diabetes

Reference: Pediatr Diabetes. 2021 Mar 21.  doi: 10.1111/pedi.13203. Online ahead of print.

Authors: Mohammed Hamdan Hashem Mohammed, Mohammad Hussain Hassan Al-Qahtani, Tim Takken

Summary: Though 12 weeks of physical activity alone improves the health of people with type 1 diabetes, there is little evidence that physical activity alone can improve glycemia in 12 weeks. The aim was to determine the effects of recreational football combined with caloric control on glycemia and cardiovascular health of adolescent boys with type 1 diabetes. The participants were divided into four groups as follows: football with diet, football-only, diet-only, and the control groups. Each group consisted of 10 participants. The football with diet and the football-only groups had 1.5 h of football twice a week for 12 weeks. The following outcomes were measured before and after 12 weeks: Glycated hemoglobin, fasting blood glucose, total cholesterol, high-density lipoprotein, low-density lipoprotein, triglycerides, and resting blood pressures. Changes were considered significant when p ≤ 0.050 and common language effect size ≤ 42 % or common language effect size ≥ 58 %. Glycated hemoglobin decreased in the football with diet group (mean change (standard deviation) = -0.9 (1.0) %, p = 0.019, and common language effect size = 31.5 %) and was different from the control group (p = 2.4×10-4 and common language effect size = 95.5 %.). However, none of the intervention groups showed a clear change in blood lipids nor blood pressure. Twelve weeks of combined football with diet intervention provides the greatest improvement in glycemia in adolescent boys with type 1 diabetes. 



#14 Kick Start to an Epidemiological Report of Soccer-Related Craniofacial Trauma Analysis

Reference: J Craniofac Surg. 2021 Mar 17.  doi: 10.1097/SCS.0000000000007639. Online ahead of print.

Authors: John V Nahas, Melinda J Choi, Erin M Wolfe, Randall G Pierrot, Benjamin R Slavin, Ethan L Plotsker, Prakash J Mathew, Seth R Thaller

Summary: Soccer is a global sport played by millions annually with an increasing popularity in the United States. Game is played by a wide range of participants from all ages and levels of competition. This scenario leads to a potential disparity in the injury profile based on quantifiable demographics. As the game continues to grow, injury detection and side-line assessment must change as well. Utilizing a national injury database, a retrospective cohort study was conducted using 10 years of data collected from randomly selected emergency departments across the United States. Patient demographics, injury sites, and diagnosis were recorded. Diagnoses examined included concussion, contusion or abrasion, dental injury, fracture, hematoma, hemorrhage, internal injury, and laceration. Highest percentage of craniofacial injuries was observed in soccer players between the ages of 12 and 18. In ages 6 to 11 the most common injuries were contusions and dental injuries, with a significantly low number of fractures. Within the age group of 12 to 18 the highest percentage of injuries was concussions. Finally, the highest percentage of injury in the ages of 19 to 34 were fractures and lacerations. There is a shift in injury profile as the age of soccer players increases and the level of play becomes faster-paced. In youth players, there is a higher percentage of soft tissue injury. Older players are more likely to suffer a higher degree of injury including fractures, concussions, and lacerations. This suggests a great utility for a layperson-friendly educational intervention initiative applicable to all demographics for the sport of soccer.






How Relative Age Effects Associate with Football Players’ Market Values: Indicators of Losing Talent and Wasting Money

In football, annual age-group categorization leads to relative age effects (RAEs) in talent development. Given such trends, relative age may also associate with market values. This study analyzed the relationship between RAEs and market values of youth players.





Effects of Age on Match-related Acceleration and Deceleration Efforts in Elite Soccer Players

The aim of this study was to examine the effects of chronological age on acceleration and deceleration match performance in professional footballers.





Latest research in football - week 23 - 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 Effects of a Congested Fixture Period on Speed and Power Performance of Elite Young Soccer Players 

Reference: Int J Sports Physiol Perform. 2021 Mar 10;1-7. doi: 10.1123/ijspp.2020-0280. Online ahead of print. 

Authors: Tomás T Freitas, Lucas A Pereira, Valter P Reis, Victor Fernandes, Pedro E Alcaraz, Paulo H S M Azevedo, Irineu Loturco 

Summary: The purpose was to investigate the effects of a match-congested period on straight and curve sprint performance, change of direction (COD) speed and deficit, vertical jumping ability, and half-squat (HS) mean propulsive power (MPP) output in young soccer players. A total of 15 under-20 elite male soccer players participated in 14 matches over 8 weeks. The following assessments were performed before and after the congested fixture period: squat and countermovement jumps, 17-m linear sprint, curve sprint test for the "good" (CSGS) and "weak" (CSWS) sides, modified 17-m Zigzag test, and HS MPP. Magnitude-based inferences and a paired t test were used to analyze pre-post changes in the assessed variables. Very likely (P < .05) decreases were noticed in 17-m sprint velocity (effect size [ES] [90% confidence limit; CL], -0.56 [-0.32 to -0.81]) and CSGS (ES [90% CL], -0.72 [-0.40 to 1.03]) after the 8-week period. A possible but nonsignificant impairment was revealed in CSWS (ES [90% CL], -0.18 [0.03 to -0.39]), and countermovement jump (ES [90% CL], -0.21 [-0.54 to 0.12]). Zigzag velocity (ES [90% CL], -2.90 [-2.45 to -3.36]) and COD deficit (ES [90% CL], 0.86 [0.52 to 1.20]) were almost certainly and significantly (P < .05) reduced and increased, respectively, after the match-congested period. An almost certain and significant (P < .05) reduction was found in HS MPP (ES [90% CL], -1.18 [-0.76 to -1.61]). Straight and curve sprint velocity, COD speed and deficit, and HS MPP were impaired after the match-congested period. Vertical jump height was possibly decreased. Seasonal phases comprising high volumes of soccer-specific training and competition seem to be detrimental to speed-power qualities in under-20 elite soccer players. 



#2 Case Report: Return to Sport Following the COVID-19 Lockdown and Its Impact on Injury Rates in the German Soccer League 

Reference: Front Sports Act Living. 2021 Feb 18;3:604226. doi: 10.3389/fspor.2021.604226. eCollection 2021. 

Authors: Dhruv R Seshadri, Mitchell L Thom, Ethan R Harlow, Colin K Drummond, James E Voos

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Summary: The Bundesliga made headlines for becoming the first major sports league to return to sport worldwide following COVID-19 lockdown. To-date, there lacks retrospective studies on longitudinal injury rates to elucidate the effect isolation measures had on the health and safety of professional athletes. This study sought to compare injury rates experienced by Bundesliga athletes before and after the COVID-19 lockdown. Data was collected from public injury and player reports regarding the Bundesliga, with injury defined as trauma resulting in loss of game time. Descriptive statistics were used to present differences in injury incidence between all Bundesliga Match days pre- and post-lockdown. Between the league's resumption and completion on May 16 and June 27, 2020, injuries occurred in 21 forwards (FW), 11 central midfielders (CM), 12 wide midfielders (WM), 16 central defenders (CD), 6 fullbacks (FB), and 2 goalkeepers. Players had 1.13 (95% CI 0.78, 1.64) times the odds of being injured following the COVID-19 lockdown, with a 3.12 times higher rate of injury when controlling for games played compared to injury rates pre-lockdown (0.84 injuries per game vs. 0.27 injuries per game). The most frequent injury group was muscular injuries with 23 injuries total, with 17% of athletes experiencing injury during their first competitive match following lockdown. Injury rate increased over 3-fold following COVID-19 lockdown. Athletes did not experience an increased rate of injury with more cumulative competitive matches played. High injury incidence for players yet to complete their first competitive match may imply suboptimal sport readiness following home confinement. 



#3 Spontaneous Pneumomediastinum in an Adolescent Soccer Player 

Reference: J Sports Sci Med. 2021 Mar 1;20(1):52-55. doi: 10.52082/jssm.2021.52. eCollection 2021 Mar. 

Authors: Akinori Kobayakawa, Hideki Hiraiwa, Shinya Ishizuka, Satoshi Yamashita, Hiroki Oba, Yusuke Kawamura, Takefumi Sakaguchi, Masaru Idota, Takahiro Haga, Takafumi Mizuno, Itaru Kawashima, Kanae Kuriyama, Shiro Imagama

Summary: Spontaneous pneumomediastinum (SPM) is an uncommon and usually benign self-limiting clinical disorder found in young people, often without apparent precipitating factors or diseases. A pressure gradient exists between the peripheral pulmonary alveoli and the hilum, and increased intra-alveolar pressure causes rupture of the terminal alveoli. We present the case of a 15-year-old male soccer player who presented with a complaint of anterior chest pain and dysphagia after stopping the strong ball with his chest. His symptom gradually progressed over hours. We can make the diagnosis of SPM using by chest X-ray and computed tomography (CT) scanning. His symptoms were gradually resolved over the course of approximately one week with no exercise and careful observation. We believe that our case provides very useful information to alert clinicians and coaches regarding this rare disease that may occur in anyone including adolescent soccer players. 



#4 Attacking Key Performance Indicators in Soccer: Current Practice and Perceptions from the Elite to Youth Academy Level 

Reference: J Sports Sci Med. 2021 Mar 1;20(1):158-169. doi: 10.52082/jssm.2021.158. eCollection 2021 Mar. 

Authors: Mat Herold, Matthias Kempe, Pascal Bauer, Tim Meyer

Summary: Key Performance Indicators (KPIs) are used to evaluate the offensive success of a soccer team (e.g. penalty box entries) or player (e.g. pass completion rate). However, knowledge transfer from research to applied practice is understudied. The current study queried practitioners (n = 145, mean ± SD age: 36 ± 9 years) from 42 countries across different roles and levels of competition (National Team Federation to Youth Academy levels) on various forms of data collection, including an explicit assessment of twelve attacking KPIs. 64.3% of practitioners use data tools and applications weekly (predominately) to gather KPIs during matches. 83% of practitioners use event data compared to only 52% of practitioners using positional data, with a preference for shooting related KPIs. Differences in the use and value of metrics derived from positional tracking data (including Ball Possession Metrics) were evident between job role and level of competition. These findings demonstrate that practitioners implement KPIs and gather tactical information in a variety of ways with a preference for simpler metrics related to shots. The low perceived value of newer KPIs afforded by positional data could be explained by low buy-in, a lack of education across practitioners, or insufficient translation of findings by experts towards practice. 



#5 Fitness and Performance Testing of Male and Female Beach Soccer Players-A Preliminary Investigation 

Reference: Front Sports Act Living. 2021 Feb 23;3:636308. doi: 10.3389/fspor.2021.636308. eCollection 2021. 

Authors: Malte N Larsen, Georgios Ermidis, João Brito, Cecilie Ørner, Clarice Martins, Luís Filipe Lemos, Peter Krustrup, Vincenzo Rago

Summary: This study aimed to compare performance on sand and a firm surface and to describe the physical capacity of male and female beach soccer players. Sixty-six male and 29 female competitive beach soccer players voluntarily participated in this study. Firstly, within-subjects test scores were compared to scores on a firm surface (criterion validity; n = 15 men) and reconducted on a second occasion (reliability; n = 51 men). Secondly, the best score on sand was retained to compare test performance between ages (classified as below 20, 20-30, and above 30 years) and sexes. Performance assessments included sprint time over 5 and 15 m (once on a firm surface and twice on sand), standing long jump (SLJ, once on a firm surface and twice on sand) and Yo-Yo intermittent recovery level 1 (Yo-Yo IR1, once on a firm surface and once on sand; only data for men were available). Five-m sprint and Yo-Yo IR1 performance on sand were not correlated to performance on a firm surface (P > 0.05). Test-retest reliability was acceptable for the 15-m sprint and SLJ tests (ICC > 0.90; CV < 5%). Performance in 15-m sprint and maximal sprinting speed were moderately lower in male players aged above 30 years. compared to players aged below 30 years (d = 0.35-0.42; P < 0.05). Irrespective of the age group, weight-bearing power-based performance mass was moderately to very largely higher in male players than in female players (d = 0.42-0.88; P < 0.05). The lack of a consistent relationship between performance on sand and on a firm surface might indicate the need to develop specific test batteries for sand-based athletes. Age-related differences in physical performance were evident only in sprint capacity. Further studies are warranted to elucidate our preliminary findings and to develop the sand specific tests. 



#6 The Accuracy of a Low-Cost GPS System during Football-Specific Movements 

Reference: J Sports Sci Med. 2021 Mar 1;20(1):126-132. doi: 10.52082/jssm.2021.126. eCollection 2021 Mar. 

Authors: Emiel Schulze, Ross Julian, Sabrina Skorski

Summary: An affordable player monitoring solution could make the evaluation of external loading more accessible across multiple levels of football (soccer). The present study aimed to determine the accuracy of a newly designed and low-cost Global Positioning System (GPS) whilst performing match-specific movement patterns. Sixteen professional male football players (24 ± 3 years) were assigned a GPS device (TT01, Tracktics GmbH, Hofheim, Germany) and completed two experimental trials. In each trial, a continuous protocol including seven movements (sideways cornering, diagonal cornering, accelerating, decelerating, backwards jogging, shuttle running, and skipping) adding up to 500 m, was completed. Time-motion data was compared with criterion distance and velocity (photo-cell timing gates and radar). Validity was assessed through the standard error of the estimate (SEE) and reliability through the coefficient of variation (CV; both with 95% confidence limits). For the total distance covered during the protocol, the system was found to be valid (SEE = 3.1% [2.2; 5.8]) and reliable (intra-device CV = 2.0% [1.2; 7.6]). Similar results were found for velocity (SEE = 3.4% [2.6; 4.8], CV = 4.7% [3.2; 8.5]). In conclusion, the present GPS system, a low-cost solution, was found to be a valid and reliable tool for measuring physical loading during football-specific movements. 



#7 Past-season, pre-season and in-season risk assessment of groin problems in male football players: a prospective full-season study 

Reference: Br J Sports Med. 2021 Mar 10;bjsports-2020-102606. doi: 10.1136/bjsports-2020-102606. 

Authors: Ernest Esteve, Marti Casals, Marc Saez, Michael Skovdal Rathleff, Mikkel Bek Clausen, Jordi Vicens-Bordas, Per Hölmich, Tania Pizzari, Kristian Thorborg

Summary: We assessed past-season, pre-season and in-season risk factors to investigate their association with an in-season groin problem in male amateur football players. Past-season groin-pain information and pre-season short-lever and long-lever adductor squeeze strength were obtained at baseline, together with anthropometrics (weight, lower limb lever length) and player age. In-season hip-related and groin-related sporting function was monitored every 4 weeks using the Sports and Recreation (Sport) subscale from the Hip And Groin Outcome Score questionnaire (HAGOS (Sport)). Groin problems, including time-loss groin injuries and groin pain irrespective of time loss, were collected over a 39-week competitive in-season. We estimated relative risk (RR), and 95% credibility interval (ICr) from logistic regressions fitted in a Bayesian framework. Players (n=245) suffering from groin pain during the past-season had 2.4 times higher risk of experiencing a groin problem in the new season (2.40 RR; 95% ICr 1.5 to 3.7). This risk was reduced by 35% (0.65 RR; 95% ICr 0.42 to 0.99) per unit (N·m/kg) increase in the long-lever adductor squeeze test. Player age, short-lever squeeze test and the HAGOS (Sport) scores were not associated with the risk of a groin problem. Past-season groin pain increased the risk of a groin problem in the new in-season. This risk was reduced by higher pre-season long-lever adductor squeeze strength. Past-season groin-pain information and long-lever adductor squeeze strength can be quickly obtained during pre-season to identify players with an elevated risk of in-season groin problems. This may be key to reduce these problems in the new season. 



#8 Is there meaningful influence from situational and environmental factors on the physical and technical activity of elite football players? Evidence from the data of 5 consecutive seasons of the German Bundesliga 

Reference: PLoS One. 2021 Mar 9;16(3):e0247771. doi: 10.1371/journal.pone.0247771. eCollection 2021. 

Authors: Paweł Chmura, Hongyou Liu, Marcin Andrzejewski, Jan Chmura, Edward Kowalczuk, Andrzej Rokita, Marek Konefał

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Summary: The study aimed to identify the effects of situational (match location, match outcome and strength of team/opponent team) and environmental (ambient temperature, relative humidity, WBGT, ground and weather condition) factors on the physical and technical activity of elite football on individual playing positions. Physical and technical activity were collected from 779 football players competing in the German Bundesliga during 5 domestic seasons, from 2014/2015 to 2018/2019, totalling 1530 matches. The data on players' physical and technical activity was taken from the IMPIRE AG system. Based on the available data, 11 variables were selected to quantify the match activity profiles of players. The results showed that situational variables had major effects on the technical performance (especially number of passes performed) but minor effects on physical performance. In turn, among the analysed environmental factors, temperature is the most sensitive, which affects the Total Distance and Sprint Efforts of players in all five positions. This investigation demonstrated that, given that passing is a key technical activity in modern football, players and training staff should be particularly aware that passing maybe affected by situational variables. Professional players are able to react and adapt to various environmental conditions, modifying physical activity depending on the needs in German Bundesliga. These results could help coaches and analysts to better understand the influences of situational and environmental variables on individual playing positions during the evaluation of players' physical and technical performance. 



#9 The Diagnostic-Measurement Method-Resting Energy Expenditure Assessment of Polish Children Practicing Football 

Reference: Diagnostics (Basel). 2021 Feb 18;11(2):340. doi: 10.3390/diagnostics11020340. 

Authors: Edyta Łuszczki, Anna Bartosiewicz, Katarzyna Dereń, Maciej Kuchciak, Łukasz Oleksy, Artur Stolarczyk, Artur Mazur

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Summary: Establishing the amount of energy needed to cover the energy demand of children doing sport training and thus ensuring they achieve an even energy balance requires the resting energy expenditure (REE) to be estimated. One of the methods that measures REE is the indirect calorimetry method, which may be influenced by many factors, including body composition, gender, age, height or blood pressure. The aim of the study was to assess the correlation between the resting energy expenditure of children regularly playing football and selected factors that influence the REE in this group. The study was conducted among 219 children aged 9 to 17 using a calorimeter, a device used to assess body composition by the electrical bioimpedance method by means of segment analyzer and a blood pressure monitor. The results of REE obtained by indirect calorimetry were compared with the results calculated using the ready-to-use formula, the Harris Benedict formula. The results showed a significant correlation of girls' resting energy expenditure with muscle mass and body height, while boys' resting energy expenditure was correlated with muscle mass and body water content. The value of the REE was significantly higher (p ≤ 0.001) than the value of the basal metabolic rate calculated by means of Harris Benedict formula. The obtained results can be a worthwhile suggestion for specialists dealing with energy demand planning in children, especially among those who are physically active to achieve optimal sporting successes ensuring proper functioning of their body. 



#10 Effects of Non-Sport-Specific Versus Sport-Specific Training on Physical Performance and Perceptual Response in Young Football Players 

Reference: Int J Environ Res Public Health. 2021 Feb 18;18(4):1962. doi: 10.3390/ijerph18041962. 

Authors: Damiano Formenti, Alessio Rossi, Tindaro Bongiovanni, Francesco Campa, Luca Cavaggioni, Giampietro Alberti, Stefano Longo, Athos Trecroci

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Summary: This study aimed to compare the effects of non-sport-specific and sport-specific training methods on physical performance and perceptual response in young football players. Seventy-nine under 11 participants were selected and assigned to non-sport-specific (NSSG), sport-specific (SSG), and control (CNTG) groups. The NSSG training protocol consisted of combined stimuli based on balance, agility, and jump rope drills. The SSG training protocol included technical exercises, defensive and offensive game-based drills, and a small-sided game. The CNTG included the participants not taking part in any sport training. All participants were tested for general motor coordination (Harre test), dynamic balance (Lower Quarter Y-balance test), and dribbling before and after 10 weeks of training (NSSG and SSG) or habitual activity (CNTG). At post-intervention, perceived enjoyment was requested by the Physical Activity Enjoyment Scale (PACES). A two-way repeated measure analysis of covariance was used to detect interactions and main effects of time and groups controlling for baseline values. Whereas, a one-way analysis of variance was used to evaluate PACES-related differences between groups. NSSG gained greater improvements (p < 0.05) compared with SSG in the Harre and Lower Quarter Y-balance tests, while dribbling skills improved similarly in both groups. Regarding PACES, NSSG and SSG presented a comparable perceived enjoyment. These findings suggest that a 10-week non-sport-specific training is an enjoyable practice capable to promote greater improvements in general motor coordination and dynamic balance compared with sport-specific training in youth football players. This can occur without impairment of football-specific skills. 



#11 Prevalence of Prediabetes and Type 2 Diabetes Mellitus in Football Players: A Novel Multi Football Clubs Cross Sectional Study 

Reference: Int J Environ Res Public Health. 2021 Feb 11;18(4):1763. doi: 10.3390/ijerph18041763. 

Authors: Sultan Ayoub Meo, Abdulelah Adnan Abukhalaf, Ali Abdullah Alomar, Omar Mohammed Alessa, Omar Yassin Sumaya, Anusha Sultan Meo

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Summary: Sports offer great benefits, improving health and reducing the risk of illnesses. This study's aim was to investigate the prevalence of prediabetes and type 2 diabetes mellitus in football players compared to population based non-elite athlete control subjects. Initially 1100 male volunteers, (550) football players, and (550) population based non-elite athlete control subjects were interviewed. After socio-demographic and medical history analysis, 756 (378) nonsmoker male football players and (378) nonsmoker male control subjects were recruited. The control subjects were not involved in regular sports activities such as football, volleyball, badminton, cricket, hockey, and swimming. Participants with a known history of anemia, blood diseases, diabetes mellitus, and malignancy were excluded from the study. The mean age of football players was 31.80 ± 5.46 years, Body Mass Index (BMI) was 26.40 ± 2.08 (kg/m2), and the mean age of control subjects was 32.32 ± 4.37 years, and BMI was 26.66 ± 1.87 (kg/m2). The selected football players have been playing football for about 2 h a day, 3 days per week, and so the total mean duration of playing football was 1.08 years. American Diabetes Association (ADA) based criteria on Glycated Hemoglobin (HbA1c) was used to investigate prediabetes and type 2 diabetes mellitus. In football players the prevalence of prediabetes was 30 (7.93%) and type 2 diabetes mellitus (T2DM) was 6 (1.59%) compared to population based matched non-elite athlete control subjects where the prediabetes was 71 (18.78%) and T2DM was 89 (23.54%) (p = 0.001). Among football players there was a 7-fold decrease in T2DM compared to control subjects. Football recreational activities markedly reduce the prevalence of prediabetes and T2DM. The study findings demonstrate the benefits of football and other such sport activities and emphasize the urgent need for promoting football based physical activities as a physiological preventive strategy against the globally growing diabetes epidemic. 



#12 Can a Community-Based Football Program Benefit Motor Ability in Children with Autism Spectrum Disorder? A Pilot Evaluation Considering the Role of Social Impairments

Reference: J Autism Dev Disord. 2021 Mar 13. doi: 10.1007/s10803-021-04933-w. Online ahead of print.

Authors: Katherine Howells, Carmel Sivaratnam, Ebony Lindor, Jason He, Christian Hyde, Jane McGillivray, Rujuta B Wilson, Nicole Rinehart

Summary: This non-randomised pilot study evaluated the impact of a community football program on motor ability in children aged 5-12 years with autism spectrum disorder. Sixteen children were evaluated at baseline-and-post attendance in a football program for a varied number of weeks and compared to 19 children engaging in treatment-as-usual. Primary analyses indicated a statistically significant increase in total MABC-2, aiming and catching, and balance scores for the intervention group, with no changes in scores in the comparison group. There were no changes in manual dexterity across either group. At a between group level, the changes in aiming and catching scores were significantly greater for the intervention group. Further analyses highlighted the potential importance of social impairments regarding aiming and catching.



#13 A public health collaboration between medical professionals and Japan's professional football league for rubella awareness

Reference: J Gen Fam Med. 2020 Oct 20;22(2):104-105. doi: 10.1002/jgf2.390. eCollection 2021 Mar.

Authors: Toshinori Nishizawa, Yuko Murashima, Yuichi Nakamura, Keigo Sugisawa, Hironobu Nishiori, Kengo Nakamura, Noriyuki Amano, Gautam A Deshpande, Hiroko Arioka

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Summary: A public health collaboration between medical professionals and Japan's professional football league for rubella awareness.



#14 Polymorphism of the angiotensin converting enzyme gene (ACE-I/D) differentiates the aerobic and speed performance of football players

Reference: J Sports Med Phys Fitness. 2021 Mar 17.  doi: 10.23736/S0022-4707.21.12060-2.

Authors: Daniel B Coelho, Eduardo M Pimenta, Izinara C Rosse, Emerson C de Oliveira, Lenice K Becker, João B Ferreira-JÚnior, Lilian M Lopes, Maria R Carvalho, Emerson Silami-Garcia

Summary: The aim was to evaluate the distribution of ACE-I/D polymorphisms on Brazilian football players performance in aerobic capacity, strength, and speed tests. The participants in this study were 212 Brazilian first division male football players genotyped in DD, ID. or II. Genotyping of DNA from leucocytes was performed using polymerase chain reaction and restriction fragment length polymorphism methods. We evaluated speed using a 30-m sprint test with speed measured at 10 m (V10), 20 m (V20), and 30 m (V30); muscular strength using counter-movement-jump and squat jump tests; and aerobic endurance using the Yo-Yo endurance test. The athletes were ranked in ascending order according to their performance in each test and divided into quartiles: first quartile (0-25%, Weak), second (25-50%, Normal), third (50-75%, Good), and fourth (75-100%, Excellent); these were clustered according to genotype frequency. We identified significant differences in the V20 test values and in the aerobic capacity test. Higher frequencies of the ACE-DD genotype were observed in the Excellent performance group in the V20. In the aerobic capacity test, higher frequencies of the ACE-II genotype were observed in Excellent and Good performance groups. Players with higher performance in anaerobic and aerobic tests are ACE-DD and ACE-II genotypes, respectively.



#15 Process Mining of Football Event Data: A Novel Approach for Tactical Insights Into the Game

Reference: Front Artif Intell. 2020 Jul 14;3:47.  doi: 10.3389/frai.2020.00047. eCollection 2020.

Authors: Pavlina Kröckel, Freimut Bodendorf

Summary: The paper explores process mining and its usefulness for analyzing football event data. We work with professional event data provided by OPTA Sports from the European Championship in 2016. We analyze one game of a favorite team (England) against an underdog team (Iceland). The success of the underdog teams in the Euro 2016 was remarkable, and it is what made the event special. For this reason, it is interesting to compare the performance of a favorite and an underdog team by applying process mining. The goal is to show the options that these types of algorithms and visual analytics offer for the interpretation of event data in football and discuss how the gained insights can support decision makers not only in pre- and post-match analysis but also during live games as well. We show process mining techniques which can be used to gain team or individual player insights by considering the types of actions, the sequence of actions, and the order of player involvement in each sequence. Finally, we also demonstrate the detection of typical or unusual behavior by trace and sequence clustering.






Observed and predicted ages at peak height velocity in soccer players

The purpose of the study was to evaluate predicted maturity offset (time before age at PHV) and age at PHV (chronological age [CA] minus maturity offset) in a longitudinal sample of 58 under-13 club level soccer players in central Portugal for whom ages at PHV were estimated with the SITAR model.





Motion Analysis of Match Play in U14 Footballers: Influence of Position, Competitive Level and Contextual Variables

This study aimed to investigate match running performance in U14 male soccer players in Norway, and the influence of position, competitive level and contextual factors on running performance.





Latest research in football - week 22 - 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 Effect of training day, match, and length of the microcycle on the worst-case scenarios in professional soccer players 

Reference: Res Sports Med. 2021 Mar 4;1-14. doi: 10.1080/15438627.2021.1895786. Online ahead of print. 

Authors: José M Oliva-Lozano, Carlos D Gómez-Carmona, Daniel Rojas-Valverde, Víctor Fortes, José Pino-Ortega

Summary: This study aimed to describe in-season worst-case scenarios (WCS) of professional soccer players and compare the WCS between training and match days (MD), considering the length of microcycle. A cohort study was designed for four competitive mesocycles in LaLiga123. The WCS of distance covered (DIS), high-speed running distance (HSRD), and sprinting distance (SPD) for four different WCS durations (1', 3', 5', 10') were analysed. Statistical differences between the WCS from training and MD were found at all intensities and periods. The magnitude of differences was moderate in DIS-1' (F= 15.49; p< 0.01; ωp2= 0.09) and DIS-3' (F= 20.99; p< 0.01; ωp2= 0.12), and high in the rest of variables (F= 26.53-89.41; p< 0.01; ωp2= 0.15-0.38). Specifically, the WCS from MD reported the highest values at all intensities and periods. Regarding training days, the greatest WCS of DIS, HSRD, and SPD were found on MD-4, MD-3, and MD+1. Considering the length of microcycle, significant differences (p< 0.05) in training-days' WCS, but not in MD (p> 0.05). In conclusion, specific WCS training programmes (e.g., including 1 min to 10-min training drills in MD-4) may be useful to prepare the demands required on MD. 



#2 The distribution of match activities relative to the maximal intensities in elite soccer players: implications for practice 

Reference: Res Sports Med. 2021 Mar 3;1-12. doi: 10.1080/15438627.2021.1895788. Online ahead of print. 

Authors: Andrea Riboli, Fabio Esposito, Giuseppe Coratella

Summary: The purpose was to determine the distribution of match-activities relative to maximum-intensities during official match in elite soccer players. One hundred and forty-eight Italian Serie A soccer players were monitored during 46 official matches (680 individual-samples). Total distance (TD), high-speed running (HSR), very high-speed running (VHSR), sprint, acceleration and deceleration were calculated. Maximum-intensities (1-minpeak) were used as the reference value to determine the distribution of relative intensity across the whole-match demands (90-minavg). Time and distance higher than 90-minavg (>90-minavg) were also calculated. The relative (m·min-1) 90-minavg vs1-minpeak was 59.6(4.4)% for TD, 26.2(4.4)% for HSR, 16.0(3.5)% for VHSR, 9.3(2.3)% for sprint, 19.2(4.6)% for acceleration and 15.4(5.2)% for deceleration. Total distance covered >90-minavg was ~61.4(5.0)% for TD, ~68.6(1.9)% for HSR, ~80.2(1.3)% for VHSR, ~95.7(0.4)% for sprint, ~75.5(1.3)% for acceleration and ~64.0(2.6)% for deceleration. With the exception of small [ES: 0.50 (0.26 to 0.73)] difference for acceleration, the relative distance >90-minavg was largely to very largely (ES: 1.64 to 7.78) higher (P< 0.05) than the 90-minavg for each metric. While no between-position difference (P> 0.05) was found for total minutes >90-minavg, between-position differences (P< 0.05) for the total distance >90-minavg were retrieved across each metric. The distribution of the activities relative to maximal intensities could assist coaches for soccer training prescriptions. 



#3 COVID-19 in Youth Soccer During Summer 2020 

Reference: J Athl Train. 2021 Mar 3. doi: 10.4085/610-20. Online ahead of print. 

Authors: Andrew M Watson, Kristin Haraldsdottir, Kevin Biese, Leslie Goodavish, Bethany Stevens, Timothy McGuine

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Summary: As sports reinitiate around the country, the incidence of COVID-19 among youth soccer athletes remains unknown. The purpose was to determine the incidence of COVID-19 among youth soccer athletes and the risk mitigation practices utilized by youth soccer organizations. Youth soccer club directors throughout the United States participated in this study. Surveys were completed in late August 2020 regarding phase of return to soccer (individual only, group non-contact, group contact), date of reinitiation, number of players, cases of COVID-19, and risk reduction procedures being implemented. Case and incidence rates were compared to national pediatric data and county data from the prior 10 weeks. A negative binomial regression model was developed to predict club COVID-19 cases with local incidence rate and phase of return as covariates and the log of club player-days as an offset. 124 respondents had reinitiated soccer, representing 91,007 players with a median duration of 73 days (IQR: 53-83 days) since restarting. Of the 119 that had progressed to group activities, 218 cases of COVID-19 were reported among 85,861 players. Youth soccer players had a lower case rate and incidence rate than children in the US (254 v. 477 cases per 100,000; incidence rate ratio [IRR]=0.511, 95% CI = [0.40-0.57], p<0.001) and the general population from the counties where data was available (268 v. 864 cases per 100,000; IRR=0.202 [0.19-0.21], p<0.001). After adjusting for local COVID-19 incidence, there was no relationship between club COVID-19 incidence and phase of return (non-contact: b=0.35±0.67, p=0.61; contact: b=0.18±0.67, p=0.79). Soccer clubs reported utilizing a median of 8 (IQR: 6-10) risk reduction procedures. The incidence of COVID-19 among youth soccer athletes is relatively low when compared to the background incidence among children in the United States in summer of 2020. No relationship was identified between club COVID-19 incidence and phase of return to soccer. 



#4 Facial Fractures Related to Soccer: A Review 

Reference: J Craniofac Surg. 2021 Mar 1. doi: 10.1097/SCS.0000000000007575. Online ahead of print. 

Authors: Murilo Sagrbi Secanho, Balduino Ferreira Menezes Neto, Leticia Perez Mazzoni, Larissa Perez Mazzoni, Felipe Lucas Parra, Aristides Augusto Palhares Neto 

Summary: Soccer is one of the most popular sports in the world. Despite the concept that soccer is not a violent game, it can lead to several injuries in amateur and professional settings, including facial fractures. Previous studies of facial fractures in soccer were all retrospective and, to date, no prospective studies are available in the literature. The authors performed a comprehensive literature search using the terms "soccer" AND "facial fracture" OR "craniofacial fracture" and "football" AND "facial fracture" OR "craniofacial fracture" and retrieved 693 articles. After applying inclusion and exclusion criteria, 11 articles were included in the present study.A total of 647 patients had suffered facial trauma, with a male-to-female ratio of 63.7:1. The patients' mean age was 27.3 years.The articles reported 670 fractures as follows: 219 (32.7%) in the zygoma, 197 (29.4%) in the nasal bone, 153 (23.6%) in the mandibula, 54 (8.0%) in the orbital wall, 12 (1.8%) in the frontal sinus, 10 (1.5%) in the alveolar bone, 3 (0.4%) in the maxilla, 3 (0.4%) in a Le Fort pattern, and 1 (0.1%) in a naso-orbito-ethmoid (NOE) pattern.Sports are a frequent cause of maxillofacial trauma and are responsible for 9.2% to 33.2% of such injuries. Soccer is a contact sport more associated with lower-limb injuries, but with a significant rate of facial fractures. As soccer is a popular sport played without facial protection and involving high-intensity movements and contact, the prevention of facial fractures related to this sport is crucial to improve the players' safety. 



#5 Curve Sprint in Elite Female Soccer Players: Relationship with Linear Sprint and Jump Performance 

Reference: Int J Environ Res Public Health. 2021 Feb 26;18(5):2306. doi: 10.3390/ijerph18052306. 

Authors: Ronaldo Kobal, Tomás T Freitas, Alberto Fílter, Bernardo Requena, Renato Barroso, Marcelo Rossetti, Renato M Jorge, Leonardo Carvalho, Lucas A Pereira, Irineu Loturco

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Summary: The aim of this study was to examine the associations between linear sprint, curve sprint (CS), change of direction (COD) speed, and jump performance in a sample of 17 professional female soccer players. All athletes performed squat and countermovement jumps, single leg horizontal triple jumps, 17 m linear sprints, CS tests, and a 17 m Zigzag COD test. A Pearson product-moment test was performed to determine the relationships among the assessed variables. The significance level was set at p < 0.05. Nearly perfect associations (r > 0.9) were found between linear and CS velocities. Players faster in linear sprints and CS exhibited greater COD deficits. No significant associations were found between COD deficit and either body mass or sprint momentum. Jumping ability was significantly correlated with linear sprint and CS performance, but not to COD performance. These findings may be used by coaches and practitioners to guide testing and training prescriptions in this population. The associations observed here suggest that training methods designed to improve linear sprint and CS velocities may benefit from the implementation of vertically and horizontally oriented plyometric exercises. 



#6 Effects of an eccentric overload and small-side games training in match accelerations and decelerations performance in female under-23 soccer players

Reference: J Sports Med Phys Fitness. 2021 Mar;61(3):365-371. doi: 10.23736/S0022-4707.20.11232-5.

Authors: Fabio Nevado-Garrosa, Víctor Torreblanca-MartÍnez, Víctor Paredes-HernÁndez, Juan Del Campo-Vecino, Carlos Balsalobre-FernÁndez

Summary: The aims of this study were: 1) to investigate the impacts that an eccentric overload training (EOT) and a small-side game training (SSGT) have on the characteristics of the accelerations (ACC) and decelerations (DCC) of the players in a soccer match; and 2) to determine if EOT and SSGT could affect the ACC and DCC reduction over time in a soccer match. Twenty-three female soccer players from a Spanish professional club were split into three groups: a small-sided game training group (SGG), an eccentric overload training group (EOG) and a control group (CG). The SSG improved the high intensity distance performed (ES [CI]=0.72 [0.22; 1.22]), the number of high intensity actions (ES [CI]=0.65 [0.01; 1.29]), the percentage of repeated high intensity actions (ES [CI]=0.54 [-0.17; 1.25]), the initial velocity of the ACC (ES [CI]=0.55 [-0.08; 1.17]) and the percentage of repeated accelerations (ES [CI]=0.87 [-0.18; 1.91]) with respect to the control group. The EOG obtained better results in distance travelling accelerating (ES [CI]=0.84 [0.09; 1.60]) and decelerating (ES [CI]=0.87 [0.23; 1.51]) above 3 m/s2, maximum ACC (ES [CI]=1.92 [0.90; 2.94]) and DCC (ES [CI]=1.29 [0.44; 2.14]) and the average of maximum ACC (ES [CI]=0.89 [0.23; 1.54]) and DCC (ES [CI]=1.08 [0.62; 1.55]) with respect to the CG. A decrement in the ACC and DCC performance was observed between the first and last 15 minutes of the competition, except for the EOG. The SSG obtained mainly improvements in variables related with efforts repetitions and the capacity of maintaining the ACC and the DCC over time, while improvements in the EOG were related to intensity in the ACC and DCC. 



#7 Using Soccer Games as an Instrument to Forecast the Spread of COVID-19 in Europe 

Reference: Financ Res Lett. 2021 Feb 23;101992. doi: 10.1016/ Online ahead of print. 

Authors: Juan-Pedro Gómez, Maxim Mironov

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Summary: We provide strong empirical support for the contribution of soccer games held in Europe to the spread of the COVID-19 virus in March 2020. We analyze more than 1,000 games across 194 regions from 10 European countries. Daily cases of COVID-19 grow significantly faster in regions where at least one soccer game took place two weeks earlier, consistent with the existence of an incubation period. These results weaken as we include stadiums with smaller capacity. We discuss the relevance of these variables as instruments for the identification of the causal effect of COVID-19 on firms, the economy, and financial markets. 



#8 Marker location and knee joint constraint affect the reporting of overhead squat kinematics in elite youth football players 

Reference: Sports Biomech. 2021 Mar 5;1-18. doi: 10.1080/14763141.2021.1890197. Online ahead of print. 

Authors: Lara M Coyne, Micheál Newell, Marco J M Hoozemans, Andrew Morrison, Susan J Brown

Summary: Motion capture systems are used in the analysis and interpretation of athlete movement patterns for a variety of reasons, but data integrity remains critical regardless. The extent to which marker location or constraining degrees of freedom (DOF) in the biomechanical model impacts on this integrity lacks consensus. Ten elite academy footballers performed bilateral overhead squats using a marker-based motion capture system. Kinematic data were calculated using four different marker sets with 3DOF and 6DOF configurations for the three joint rotations of the right knee. Root mean squared error differences between marker sets ranged in the sagittal plane between 1.02 and 4.19 degrees to larger values in the frontal (1.30-6.39 degrees) and transverse planes (1.33 and 7.97 degrees). The cross-correlation function of the knee kinematic time series for all eight marker-sets ranged from excellent for sagittal plane motion (>0.99) but reduced for both coronal and transverse planes (<0.9). Two-way ANOVA repeated measures calculated at peak knee flexion revealed significant differences between marker sets for frontal and transverse planes (p < 0.05). Pairwise comparisons showed significant differences between some marker sets. Marker location and constraining DOF while measuring relatively large ranges of motion in this population are important considerations for data integrity. 



#9 Performance Analysis in Football-Specific Tests by Para-Footballers With Cerebral Palsy: Implications for Evidence-Based Classification 

Reference: Int J Sports Physiol Perform. 2021 Mar 3;1-7. doi: 10.1123/ijspp.2020-0370. Online ahead of print. 

Authors: Javier Yanci, Daniel Castillo, Aitor Iturricastillo, Astrid Aracama, Alba Roldan, Raúl Reina 

Summary: The objectives of this study were to analyze whether there were differences among para-footballers with different types and degrees of brain impairment (ie, bilateral spasticity, athetosis/ataxia, unilateral spasticity, minimum impairment criteria, or no impairment) in performing 3 football-specific tests requiring ball dribbling, to analyze whether there was an association among the results obtained in the 3 tests, and to determine whether the performance in the tests was associated with competitive level, level of training, or years' experience in para-footballers with cerebral palsy (CP). A total of 123 footballers took part in the study, 87 of whom were footballers with CP and 36 who were without impairment. Both groups were assessed in 3 football-specific tests (Stop and Go, Turning and Dribbling, and the Illinois Agility Test). The results showed that the footballers without impairment recorded a better performance in all tests (P < .01) in comparison with the CP players. No significant differences in test performance were observed among the CP players from different competitive levels. However, significant differences (P < .01) were observed between players with diplegia or athetosis/ataxia compared with players with hemiplegia or minimum impairment level. Performance in the tests did not correlate with years of football experience, weekly strength training sessions, or specific football training in the footballers with CP (P = .12-.95). These findings suggest the possible inclusion of these tests in the classification process for footballers with CP because they discriminate among functional classes and are resistant to training and competitive level. 



#10 Common international trends in football stadium attendance 

Reference: PLoS One. 2021 Mar 3;16(3):e0247761. doi: 10.1371/journal.pone.0247761. eCollection 2021. 

Authors: Jan C van Ours

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Summary: This paper examines long-term developments in stadium attendance in professional football in the Netherlands. As in many other European countries attendance had a U-shaped development with the lowest numbers in the mid-1980s. The developments in the Netherlands do not seem to have been affected by hooliganism but by socioeconomic factors. Furthermore, the association with stadium attendance in other European leagues in particular the English Premier League is very high. This suggests that stadium attendance is affected not only by national developments but also by common international trends in the interest in football matches. 



#11 Determinants of lower-extremity injury severity and recovery in U.S. High School Soccer Players 

Reference: Res Sports Med. 2021 Mar 7;1-11. doi: 10.1080/15438627.2021.1895782. Online ahead of print. 

Authors: Avinash Chandran, Angelo Elmi, Heather Young, Loretta DiPietro

Summary: Lower-extremity injuries are common among soccer players, yet few studies have attempted to identify determinants of lower-extremity injury severity and recovery within this group. We aim to identify determinants of lower-extremity injury severity and recovery among high school (HS) soccer players in the US. We used soccer-related injury observations recorded within the NATION-SP during 2011/12-2013/14. Odds of a season-ending game-related injury were higher than a season-ending practice-related injury (Adj. OR = 2.64, 95% CI = [1.39, 5.01]). Gender, setting, and playing surface emerged as significant determinants of any time loss following lower-extremity injuries in multivariable logistic regression models, and multivariable random effects Poisson regression models also revealed significant differences in recovery durations across levels of these variables for "similarly severe" injuries. Findings suggest that gender, injury setting, playing surface contribute to injury corollaries differently. Similar multi-method approaches are needed to identify determinants of injury severity and recovery in this group. 



#12 The Relationships Between Perceived Wellness, Sleep, and Acute: Chronic Training Load in National Collegiate Athletics Association Division I Male Soccer Players 

Reference: J Strength Cond Res. 2021 Mar 3. doi: 10.1519/JSC.0000000000004003. Online ahead of print. 

Authors: Yasuki Sekiguchi, Ryan M Curtis, Robert A Huggins, Courteney L Benjamin, Alan J Walker, Shawn M Arent, William M Adams, Travis Anderson, Douglas J Casa 

Summary: The purpose of this study was to investigate relationships between perceived wellness, sleep, and acute: chronic workload ratio (ACWR) throughout a collegiate men's soccer season. Sixty male collegiate soccer players (mean[M] ± SD; age, 21±2 year; body mass, 77.6 ± 6.5 kg; height, 180.1 ± 6.4 cm; body fat%, 9.9 ± 3.9% ; and V[Combining Dot Above]O2max, 53.1 ± 5.0 ml·kg-1·min-1) participated in this study. During each session, players used a heart rate and global positioning satellite-enabled chest strap to measure training impulse and ACWR. The ACWR values were trichotomized at the individual level giving an equal number of observations within each ACWR category of low, moderate, and high ACWR (M ± SD; low, 0.658 ± 0.23; moderate, 0.92 ± 0.15; and high, 1.17 ± 0.16). Stress, fatigue, and soreness levels were collected using 1-10 Likert scales and sleep duration, and sleep quality were measured by the Karolinska Sleep Diary. Stress, fatigue, soreness levels, and sleep quality were transformed to corresponding z-scores at the individual level. Fatigue levels were significantly higher when ACWR was high compared with low (mean difference [95% confidence intervals], effect size, p-value; 0.31 [0.21, 0.42], 0.29, p < 0.001) and moderate (0.14 [0.03, 0.24], 0.13, p = 0.01). Fatigue levels were also significantly higher when the ACWR was moderate compared with low (0.18 [0.07, 0.28], 0.16, p = 0.001). Soreness levels were significantly higher when the ACWR was high compared with low (0.25 [0.14, 0.36], 0.23, p < 0.001). Stress levels were significantly greater when the ACWR was high compared with low (0.19, [0.08, 0.29], 0.18, p < 0.001) and compared with moderate (0.15, [0.05, 0.25], 0.14, p = 0.004). There were no differences in sleep duration or sleep quality in different ACWR. The ACWR may be a useful tool to achieve an appropriate balance between training and recovery to manage daily fatigue and soreness levels in athletes. 



#13 Relationship Between External Load and Self-Reported Wellness Measures Across a Men's Collegiate Soccer Preseason 

Reference: J Strength Cond Res. 2021 Mar 3. doi: 10.1519/JSC.0000000000003997. Online ahead of print. 

Authors: Jennifer B Fields, Diane M Lameira, Jerome L Short, Justin M Merrigan, Sina Gallo, Jason B White, Margaret T Jones 

Summary: Monitoring athlete training load is important to training programming and can help balance training and recovery periods. Furthermore, psychological factors can affect athlete's performance. Therefore, the purpose was to examine the relationship between external load and self-reported wellness measures during soccer preseason. Collegiate men soccer athletes (n = 20; mean ± SD age: 20.3 ± 0.9 years; body mass: 77.9 ± 6.8 kg; body height: 178.87 ± 7.18cm; body fat: 10.0 ± 5.0%; V[Combining Dot Above]O2max: 65.39 ± 7.61ml·kg-1·min-1) participated. Likert scale self-assessments of fatigue, soreness, sleep, stress, and energy were collected daily in conjunction with the Brief Assessment of Mood (vigor, depression, anger, fatigue, and confusion). Total distance (TD), player load (PL), high-speed distance (HSD, >13 mph [5.8 m·s-1]), high inertial movement analysis (IMA, >3.5 m·s-2), and repeated high-intensity efforts (RHIEs) were collected in each training session using positional monitoring (global positioning system/global navigation satellite system [GPS/GNSS]) technology. Session rate of perceived exertion (sRPE) was determined from athlete's post-training rating (Borg CR-10 Scale) and time of training session. Multilevel models revealed the bidirectional prediction of load markers on fatigue, soreness, sleep, energy, and sRPE (p < 0.05). Morning ratings of soreness and fatigue were predicted by previous afternoon's practice measures of TD, PL, HSD, IMA, RHIE, and sRPE. Morning soreness and fatigue negatively predicted that day's afternoon practice TD, PL, HSD, IMA, RHIE, and sRPE. Morning ratings of negative mood were positively predicted by previous day's afternoon practice HSD. In addition, negative morning mood states inversely predicted HSD (p = 0.011), TD (p = 0.002), and PL (p < 0.001) for that day's afternoon practice. Using self-reported wellness measures with GPS/GNSS technology may enhance the understanding of training responses and inform program development. 



#14 Quality of Life: Changes in Self-Perception in People with down Syndrome as a Result of Being Part of a Football/Soccer Team. Self-Reports and External Reports 

Reference: Brain Sci. 2021 Feb 12;11(2):226. doi: 10.3390/brainsci11020226. 

Authors: Rocío Camacho, Cristina Castejón-Riber, Francisco Requena, Julio Camacho, Begoña M Escribano, Arturo Gallego, Roberto Espejo, Amaranta De Miguel-Rubio, Estrella I Agüera

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Summary: The hypothesis posed was whether being part of a football/soccer team influenced the quality of life (QL) of the people who participated in it since their perception of themselves is enhanced by factors, such as self-determination, social inclusion, emotional well-being, physical well-being, material well-being, rights, personal development, and internal relationships. The objective was to evaluate the QL of people with Down Syndrome (DS) using their self-perception (n = 39) and the perception of the informants (family members, teachers) (n = 39). The KidsLife-Down Scale, with a few modifications, was used. In general, differences of opinion between the subgroups of participants with DS and informants showed that results were higher in terms of perception for participants in the DS subgroup. Scores for all variables were higher for those participants with DS who said they did engage in practicing competitive football/soccer. Although the perception of informants provides a great deal of information regarding the QL of participants with DS, participants with DS should also be involved in the evaluation process and their self-perceptions taken into account. It is not participating in a football team that causes the conclusions of the study, but training (which includes the friendly matches that are played), the cause correlated with the improvements detected in the athlete's DS. 



#15 Comparison of Running Distance Variables and Body Load in Competitions Based on Their Results: A Full-Season Study of Professional Soccer Players 

Reference: Int J Environ Res Public Health. 2021 Feb 20;18(4):2077. doi: 10.3390/ijerph18042077. 

Authors: Hadi Nobari, Rafael Oliveira, João Paulo Brito, Jorge Pérez-Gómez, Filipe Manuel Clemente, Luca Paolo Ardigò

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Summary: The aims of this study were to compare the external workload in win, draw and defeat matches and to compare first and second halves in the Iranian Premier League. Observations on individual match performance measures were undertaken on thirteen outfield players (age, 28.6 ± 2.7 years; height, 182.1 ± 8.6 cm; body mass, 75.3 ± 8.2 kg; BMI, 22.6 ± 0.7 kg/m2) competing in the Iranian Premier League. High-speed activities selected for analysis included total duration of matches, total distance, average speed, high-speed running distance, sprint distance, maximal speed and GPS-derived body load data. In general, there were higher workloads in win matches when compared with draw or defeat for all variables; higher workloads in the first halves of win and draw matches; higher total distance, high-speed running distance and body load in the second half in defeat matches. Specifically, lower average speed was found in matches with a win than with draw or defeat (p < 0.05). Sprint distance was higher in the first half of win than defeat matches and high-speed running distance was lower in draw than defeat matches (all, p < 0.05). In addition, first half presented higher values for all variables, regardless of the match result. Specifically, high-speed running distance was higher in the first half of matches with a win (p = 0.08) and total distance was higher in the first half of matches with a draw (p = 0.012). In conclusion, match result influences the external workload demands and must be considered in subsequent training sessions and matches. 



#16 Sleep Indices and Cardiac Autonomic Activity Responses during an International Tournament in a Youth National Soccer Team 

Reference: Int J Environ Res Public Health. 2021 Feb 20;18(4):2076. doi: 10.3390/ijerph18042076. 

Authors: Pedro Figueiredo, Júlio Costa, Michele Lastella, João Morais, João Brito

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Summary: This study aimed to describe habitual sleep and nocturnal cardiac autonomic activity (CAA), and their relationship with training/match load in male youth soccer players during an international tournament. Eighteen elite male youth soccer players (aged 14.8 ± 0.3 years; mean ± SD) participated in the study. Sleep indices were measured using wrist actigraphy, and heart rate (HR) monitors were used to measure CAA during night-sleep throughout 5 consecutive days. Training and match loads were characterized using the session-rating of perceived exertion (s-RPE). During the five nights 8 to 17 players slept less than <8 h and only one to two players had a sleep efficiency <75%. Players' sleep duration coefficient of variation (CV) ranged between 4 and 17%. Nocturnal heart rate variability (HRV) indices for the time-domain analyses ranged from 3.8 (95% confidence interval, 3.6; 4.0) to 4.1 ln[ms] (3.9; 4.3) and for the frequency-domain analyses ranged from 5.9 (5.6; 6.5) to 6.6 (6.3; 7.4). Time-domain HRV CV ranged from 3 to 10% and frequency-domain HRV ranged from 2 to 12%. A moderate within-subjects correlation was found between s-RPE and sleep duration [r = -0.41 (-0.62; -0.14); p = 0.003]. The present findings suggest that youth soccer players slept less than the recommended during the international tournament, and sleep duration was negatively associated with training/match load. 



#17 Effects of Short-Term Plyometric Training on Agility, Jump and Repeated Sprint Performance in Female Soccer Players 

Reference: Int J Environ Res Public Health. 2021 Feb 25;18(5):2274. 

doi: 10.3390/ijerph18052274.

Authors: Marcin Maciejczyk, Renata Błyszczuk, Aleksander Drwal, Beata Nowak, Marek Strzała

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Summary: The aim of the study was to determine the effects of short-term (4 weeks, twice a week: 8 sessions) plyometric training on agility, jump, and repeated sprint performance in female soccer players. The study comprised 17 females performing this sports discipline. The players were randomly divided into two groups: with plyometric training (PLY) and the control (CON). All players followed the same training program, but the PLY group also performed plyometric exercises. Tests used to evaluate physical performance were carried out immediately before and after PLY. After implementing the short PLY training, significant improvement in jump performance (squat jump: p = 0.04, ES = 0.48, countermovement jump: p = 0.009, ES = 0.42) and agility (p = 0.003, ES = 0.7) was noted in the PLY group. In the CON group, no significant (p > 0.05) changes in physical performance were observed. In contrast, PLY did not improve repeated sprint performance (p > 0.05) among female soccer players. In our research, it was shown that PLY can also be effective when performed for only 4 weeks instead of the 6-12 weeks typically applied.





Whole-body energy transfer strategies during football instep kicking: Implications for training practices

We hypothesized that fatigue induced by acute workload in short and intense games, might in either of two ways: by pushing lower limbs mechanics toward injury or by inducing opposed protective compensatory adjustments. We aimed at assessing the extent to which fatigue impact on joints kinematics and kinetics while performing repeated changes of direction (CoDs) in the light of the ACL risk factors.





Key load indicators and load variability in professional soccer players: A full season study

The aims of this study were to 1) determine the key load indicators in professional soccer through principal component analysis (PCA) and 2) analyse the load variability of each training and match day within the microcycle considering the principal components.





Latest research in football - week 21 - 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 Influence of Fatigue on the Rapid Hamstring/Quadriceps Force Capacity in Soccer Players 

Reference: Front Physiol. 2021 Feb 5;12:627674. doi: 10.3389/fphys.2021.627674. eCollection 2021. 

Authors: Qingshan Zhang, Baptiste Morel, Robin Trama, Christophe A Hautier

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Summary: The objective of this study was to examine the effect of fatigue on maximal and rapid force capacities and muscular activation of the knee extensors and flexors. Seventeen professional soccer players volunteered to participate in this study. Peak torque (Tpeak) and rate of torque development (RTD) of knee flexor (90°. s-1, -30°. s-1) and extensor (90°. s-1) muscles were measured before and after fatigue (i.e., 30 maximal knee extension and flexion repetitions at 180°s-1) performed on an isokinetic dynamometer. Hamstring to quadriceps peak strength and RTD ratios were calculated. Besides, using surface EMG, the mean level of activation (RMSmean), Rate of EMG Rise (RER), and EMG Frequency-Time maps were measured on quadriceps and hamstring muscles. Following fatigue, Tpeak, RTD, RER declined significantly in the two muscle groups (all p < 0.05) without modification of RMSmean. No decrease in conventional and functional H/Q ratios was observed after fatigue except for a significant increase in the H ecc30/Q con180 ratios (1.03 ± 0.19 vs. 1.36 ± 0.33, p < 0.001). Besides, the RTD H/Q ratios decreased significantly after fatigue, and the statistical parametric mapping analysis (SPM) performed on the EMG/angle curves, and EMG Frequency-Time maps showed that fatigue strongly influenced the muscle activation during the first 100 ms of the movement, following the higher EMG frequency component shift toward the lower frequency component. Our results show that the reduction of RTD and RER during the first 100 ms of the contraction after fatigue exercise makes more sense than any H/Q ratio modification in understanding injury risk in soccer players. 



#2 Analysis of Fitness Status Variations of Under-16 Soccer Players Over a Season and Their Relationships With Maturational Status and Training Load 

Reference: Front Physiol. 2021 Feb 5;11:597697. doi: 10.3389/fphys.2020.597697. eCollection 2020. 

Authors: Hadi Nobari, Ana Filipa Silva, Filipe Manuel Clemente, Marefat Siahkouhian, Miguel Ángel García-Gordillo, José Carmelo Adsuar, Jorge Pérez-Gómez

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Summary: The purposes of this study were (i) to analyze the variations in maximal oxygen consumption (VO2m ax), maximal heart rate (HRmax), heart rate at rest, acceleration, maximal speed, agility, anaerobic sprint test (RAST) of peak power (RPP), RAST of minimum power, RAST of average power (RAP), and RAST of fatigue index (RFI) during the competitive season, using maturation status and accumulated training load as covariates, and (ii) to describe the differences between responders and non-responders in relation to baseline levels. Twenty-three elite players from the same team competing in the national under-16 competitions were evaluated for 20 weeks in period 1 (before league), middle (mid league), and period 2 (after league). The VO2m ax (p = 0.009), maximal speed (p = 0.001), RPP (p < 0.001), RAP (p < 0.001), and RFI (p < 0.001) significantly changed across the assessment periods. Interestingly, using accumulated training load and maturation status as covariates revealed no statistical significance (p > 0.05). When analyzing responders and non-responders, only HRmax (between periods 1 and 2) showed no differences between the groups. As a conclusion, it can be seen that accumulated training load and maturation status play an important role in the differences observed across the season. Thus, coaches should consider the importance of these two factors to carefully interpret fitness changes in their players and possibly adjust training decisions according to the maturation level of the players. 



#3 Physical Demands and Internal Response in Football Sessions According to Tactical Periodization 

Reference: Int J Sports Physiol Perform. 2021 Feb 24;1-7. doi: 10.1123/ijspp.2019-0829. 

Authors: Ibai Guridi Lopategui, Julen Castellano Paulis, Ibon Echeazarra Escudero 

Summary: The objectives of the present study were (1) to analyze the internal and external load profile of training and competition carried out by semiprofessional football players during a 27-week period and (2) to examine the possible link between this type of periodization and players' fitness status and their readiness to compete. Training and match data were obtained from 26 semiprofessional football players belonging to the reserve squad of a Spanish La Liga club during the 2018/19 season. For the purpose of this study, the distribution of external and internal load during a typical training microcycle, with 6 or 7 days between matches, was analyzed. Five types of sessions were considered: strength, duration, velocity, preofficial match, and official match. 

Results: The results showed a different internal and external load profile for each type of session, with the load being consistently higher during matches when compared with training sessions (28.9%-94% higher), showing significant differences in all the variables. There was a clear tapering strategy in the last days of the week to arrive with enough freshness to compete, shown by the decrease of the values in the 2 days before the match (15%-83% reduction, depending on the variable). Furthermore, the horizontal alternation of the load allowed the players to maintain their fitness level during the 27-week period. Our findings suggest that this weekly periodization approach could help achieve a double conditional target, allowing a short tapering strategy to face the match with enough freshness and serving as a strategy for maintaining or optimizing players' physical performance during the season. 



#4 Coaches' Corrective Feedback, Psychological Needs, and Subjective Vitality in Mexican Soccer Players 

Reference: Front Psychol. 2021 Feb 4;11:631586. doi: 10.3389/fpsyg.2020.631586. eCollection 2020. 

Authors: José Tristán, Rosa María Ríos-Escobedo, Jeanette M López-Walle, Jorge Zamarripa, Miguel A Narváez, Octavio Alvarez

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Summary: In the sport context, an essential aspect of an athlete's development and performance happens during the interaction with the coach while receiving information on the aspects of performance that need to be modified (corrective feedback). Grounded in the Self-Determination Theory and particularly on the basic psychological needs theory, a structural equation model (SEM) was tested with the following sequence: perception of the amount of corrective feedback generated by the coach, perceived legitimacy of corrective feedback, satisfaction of basic psychological needs, and vitality in soccer players. Additionally, simple mediation and serial (double) mediation models were also tested. Participants were 377 Mexican soccer players (Maged = 16.46, SD = 1.08), who completed the instruments that evaluated the study variables. SEM results reported positive and significant variables' interrelations in the sequence. The analysis of serial mediation model showed that the perceived legitimacy of feedback and the satisfaction of basic psychological needs fully mediated the relationship between the perception of the amount of corrective feedback generated by the coach and the perception of the subjective vitality of Mexican soccer players. Results suggest that coaches have to ensure that athletes accept the corrective feedback provided and meet their basic psychological needs. Based on SDT tenets, this research highlights the importance for coaches to be aware of the athlete's perceptions when they are providing corrective feedback and their implications for athlete's technical development and well-being. It is suggested to incorporate those aspects to training programs for coaches. 



#5 Open Interphalangeal Dislocation of the Great Toe in an Amateur Football Player: A Rare Case Report 

Reference: J Orthop Case Rep. 2020 Jul;10(4):78-81. doi: 10.13107/jocr.2020.v10.i04.1812. 

Authors: Michael-Alexander Malahias, Dimitrios Oikonomou, Vikram V Kadu, Michail Kotsapas, Nikolaos K Paschos, Dimitrios Giotis

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Summary: Open interphalangeal (IP) dislocations are completely uncommon. Up to now, different patterns of dislocation have been described. The combination of axial loading and hyperdorsiflexion forces, leading to plantar dislocation of the distal phalanx, is a rare type of injury, which has yet not been reported. A rare case of traumatic open dislocation of the left great toe IP joint in a highly active, overweighted, male, amateur football player is presented. The possible underlying mechanism was impact of the left great toe against the ground and subsequent hyperdorsiflexion. The distal phalanx was dislocated plantarly, whereas the proximal phalanx was protruding out the dorsal skin of the toe. Open exploration and reduction led to excellent clinical results 6 months after surgery. Open traumatic IP dislocation of the great toe due to low force activity is a very rare mode of injury, which requires adequate treatment including immediate purification of the exposed joint, control of the sesamoids' position, exclusion of intra-articular fractures, joint's reduction, soft-tissue repair, and proper stabilization. 



#6 The Relationship between Body Mass Index, Body Fat Percentage, and Dietary Intake with Muscle Fatigue in Adolescent Football Players 

Reference: J Nutr Sci Vitaminol (Tokyo). 2020;66(Supplement):S134-S136. doi: 10.3177/jnsv.66.S134. 

Authors: Mochammad Rizal, Calista Segalita, Trias Mahmudiono

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Summary: It is important for football players to maintain muscle strength through the entire match. The aim of this study was to investigate body mass index (BMI), body fat percentage (BF%), dietary intake (energy, carbohydrate, and protein) and its relationship with muscle fatigue among adolescent football players. This was a cross-sectional study involving 26 football players aged 15-17 y. BMI was determined using WHO Anhtro Plus, BF% was analyzed using Bioelectrical Impedance Analysis (BIA) and categorized using bodyfat curves for children, and dietary intake was assessed using 3×24 h dietary recall. Running-Based Anaerobic Sprint Test (RAST) was conducted twice and averaged to identify muscle fatigue. Pearson correlation and multiple-regression analysis were performed to determine the relationship between variables. The results showed that overall participants had healthy weight (17.61±1.82 kg/m2), good diet pattern (energy 99.08±14.34%, carbohydrate 92.88±9.54% and protein 95.96±23.41%), but low body fat (6.76±2.12%). In pearson test, negative correlations were found in muscle fatigue and BMI (r=-0.393, p=0.047), as well as BF% (r=-0.458, p=0.019), but positive between muscle fatigue and energy intake (r=0.538, p=0.005). Furthermore, multiple-regression analysis only confirmed statistically significant relationship between energy intake and muscle fatigue (p=0.028). We conclude that the higher BMI and BF% may lead to greater muscle fatigue, while higher energy intake has significant improvement to reduce muscle fatigue. Hence, it is essential for football players to consume adequate energy, and consider to maintain BMI and BF% at optimal range. 



#7 Jejunal rupture resulting from a collision in soccer 

Reference: J Surg Case Rep. 2021 Feb 15;2021(2):rjab005. doi: 10.1093/jscr/rjab005. eCollection 2021 Feb. 

Authors: Ho-Cing Victor Yau

Summary: Small bowel rupture in blunt force trauma usually results from high-velocity and high-energy forces. The occurrence of this following collision in sport is a rare event that requires urgent surgical intervention. This is the case of a 27-year-old male who sustained a jejunal rupture following a collision during a game of soccer. 



#8 Recovery Kinetics Following Small-Sided Games in Competitive Soccer Players: Does Player Density Size Matter? 

Reference: Int J Sports Physiol Perform. 2021 Feb 24;1-11. doi: 10.1123/ijspp.2020-0380. Online ahead of print. 

Authors: Konstantinos Papanikolaou, Panagiotis Tsimeas, Angeliki Anagnostou, Alexandros Varypatis, Christos Mourikis, Theofanis Tzatzakis, Dimitrios Draganidis, Dimitrios Batsilas, Theodoros Mersinias, Georgios Loules, Athanasios Poulios, Chariklia K Deli, Alexios Batrakoulis, Athanasios Chatzinikolaou, Magni Mohr, Athanasios Z Jamurtas, Ioannis G Fatouros 

Summary: The purpose was to examine the recovery kinetics of exercise-induced muscle damage (EIMD), neuromuscular fatigue, and performance following small-sided games (SSGs) of different densities in soccer. Ten male players randomly completed 3 trials: a control trial (no SSGs), 4v4 SSGs (62.5 m2/player), and 8v8 SSGs (284.4 m2/player). External and internal load were monitored using GPS technology, heart-rate monitors, and rating of perceived exertion. Delayed-onset muscle soreness (DOMS), creatine kinase (CK), isokinetic strength, countermovement jump (CMJ), and sprint were determined at baseline, as well as at 24, 48, and 72 hours post-SSGs. Neuromuscular fatigue was assessed at baseline and at 1, 2, and 3 hours post-SSGs. DOMS increased (P < .05) in 4v4 for 72 hours and in 8v8 for 24 hours with that of knee flexors being more pronounced than that of extensors. CK increased (P < .05) in 4v4 for 72 hours and in 8v8 for 24 hours. Neuromuscular fatigue increased (P < .05) in 4v4 for 2 hours and in 8v8 for 3 hours. Strength declined (P < .05) in 4v4 for 48 hours and in 8v8 for 72 hours. CMJ decreased (P < .05) in 4v4 for 24 hours and in 8v8 for 48 hours. Sprint decreased (P < .05) for 48 hours in 4v4 and for 72 hours in 8v8. SSGs are associated with a prolonged rise of EIMD and induce short-term neuromuscular fatigue and slow recovery kinetics of strength, jump, and sprinting performance. The time for complete recovery is longer for SSGs of lower density. 



#9 Reviewing the role of the environment in the talent development of a professional soccer club 

Reference: PLoS One. 2021 Feb 25;16(2):e0246823. doi: 10.1371/journal.pone.0246823. eCollection 2021. 

Authors: Vincent Gesbert, Fabienne Crettaz von Roten, Denis Hauw

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Summary: This two-part study examined the perceptions of talented Swiss soccer players about their talent development environment. The first study presented the translation and validation of the Talent Development Environment Questionnaire (TDEQ) into French using a recommended methodology for translating and culturally adapting questionnaires. Two hundred and three Swiss athletes (M = 16.99 years old) responded to the 25 items of the TDEQ-5. One item was excluded due to low factor loadings, and the descriptive statistics showed that the re-specified TDEQ-5 instrument had acceptable global model fit according to the thresholds in the literature (χ2 (df = 17) = 484.62, p<0.001, CFI = 0.91, TLI = 0.90, RMSEA = 0.07, SRMR = 0.06). This adaptation is thus valid for assessing the effectiveness of talent development processes. For the second study, a holistic design was used to examine the perceptions of a set of players embedded in a top-level Swiss soccer academy (i.e., 64 elite soccer players from 14 to 18 years old) by using the TDEQ-5. The results showed some relative strengths (i.e., F1-Long-Term Focus for the M15 and M16 age-groups) and weaknesses (i.e., F2-Alignment of Expectations for the M17 and M18 age -groups and F3-Communication for M17). They also highlighted that the talent pathways of these Swiss soccer players could not be summarized by a single type of transition toward a professional team. Rather, there were context-specific requirements, such as the critical period between the M15-M16 and M17-M18 age-groups, suggesting that when the players first entered their TDE they experienced a set of affordances to develop and flourish, which thereafter were perceived as less rich and/or abundant. These results offer a starting point for optimizing talent pathways. 



#10 Effects of Caffeine Supplementation on Physical Performance of Soccer Players: Systematic Review and Meta-Analysis 

Reference: Sports Health. 2021 Mar 5;1941738121998712. doi: 10.1177/1941738121998712. 

Authors: Raphael Einsfeld Simões Ferreira, Rafael Leite Pacheco, Carolina de Oliveira Cruz Latorraca, Rachel Riera, Ricardo Guilherme Eid, Ana Luiza Cabrera Martimbianco

Summary: Caffeine is 1 of the most popular supplements consumed by athletes, and the evidence for improving soccer performance remains limited.  The aim was to investigate and update the effects (benefits and harms) of caffeine to improve performance on soccer players. Electronic search in Medline (via PubMed), CENTRAL, Embase, SPORTDiscus, and LILACS, from inception to March 28, 2020 was performed. Randomized clinical trials (RCTs) assessing the effects of caffeine on the performance of soccer players. Data extraction was conducted independently by 2 authors using a piloted form. We assessed methodological quality (Cochrane risk-of-bias [RoB] table) and the certainty of the evidence (GRADE [Grading of Recommendations Assessment, Development and Evaluation] approach).  Sixteen RCTs were included. Overall methodological quality was classified as unclear to low risk of bias. When assessing aerobic endurance, meta-analyses did not demonstrate the differences between caffeine and placebo (mean difference [MD], 44.9 m; 95% confidence interval [CI], -77.7 to 167.6). Similarly, no difference was observed during time to fatigue test (MD, 169.8 seconds; 95% CI, -71.8 to 411.6). Considering anaerobic power, meta-analyses also did not find differences for vertical jump (MD, 1.01 cm; 95% CI, -0.68 to 2.69) and repeated sprint tests (MD, -0.02 seconds; 95% CI, -0.09 to 0.04), as well as reaction time agility test (MD, 0.02 seconds; 95% CI, -0.01 to 0.04) and rating of perceived exertion (MD, 0.16 points; 95% CI, -0.55 to 0.87). Regarding safety, a few minor adverse events were reported. Based on the GRADE approach, the certainty of this evidence was classified as very low to low. We found no significant improvement in soccer-related performance with caffeine compared with placebo or no intervention. However, caffeine appears to be safe. 



#11 Relationships Between Aerobic Performance, Hemoglobin Levels, and Training Load During Small-Sided Games: A Study in Professional Soccer Players 

Reference: Front Physiol. 2021 Feb 16;12:649870. doi: 10.3389/fphys.2021.649870. eCollection 2021. 

Authors: Saeid Younesi, Alireza Rabbani, Filipe Manuel Clemente, Rui Silva, Hugo Sarmento, António José Figueiredo

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Summary: The purposes of this study were (1) to analyze between-session variations of external and internal load measures during small-sided games (SSGs) and (2) to test the relationships between the maximum speed reached (VIFT) during the last stage of the 30-15 Intermittent Fitness Test, hemoglobin levels, and training load measures during SSG intervals among professional soccer players. Sixteen professional soccer players (mean ± SD; age 27.2 ± 3.4 years, height 174.2 ± 3.6 cm, body mass 69.1 ± 6.4 kg, and body fat 10.4 ± 4.1%) participated in this study. Hemoglobin and aerobic performance were first tested, and then a 3-week SSG program was applied using a 3 vs. 3 format. During those 3 weeks, internal and external load of entire sessions were also monitored for all training sessions. Trivial-to-small, standardized differences were observed between sessions for external and internal measures during SSGs. Total distance (TD) and mechanical work (MW) were the only variables that indicated small changes. Large-to-very-large relationships were found between VIFT and external loads: TD (r range: 0.69; 0.87), high-intensity running (HIR; r range: 0.66; 0.75), and MW (r range: 0.56; 0.68). Moderate-to-large negative relationships were found between hemoglobin levels and internal loads: Edwards' TRIMP (r range: -0.36; -0.63), %HRmax (r range: -0.50; -0.61), and red zone (r range: -0.50; -0.61). VIFT had unclear relationships with overall internal loads, while hemoglobin levels presented unclear relationships with overall external loads. In conclusion, no meaningful changes were found between sessions considering the format of play used. Additionally, the detected relationships indicate that VIFT and hemoglobin levels are good indicators of the performance capacity and physiological profile of players during SSGs. Also, the use of SSGs protocols as a monitoring complement of the 30-15IFT is suggested. 



#12 The effects of 14-week betaine supplementation on endocrine markers, body composition and anthropometrics in professional youth soccer players: a double blind, randomized, placebo-controlled trial 

Reference: J Int Soc Sports Nutr. 2021 Mar 4;18(1):20. doi: 10.1186/s12970-021-00417-5. 

Authors: Hadi Nobari, Mehdi Kargarfard, Vazgen Minasian, Jason M Cholewa, Jorge Pérez-Gómez

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Summary: Betaine supplementation may enhance body composition outcomes when supplemented chronically during an exercise program. The purpose of this study was to evaluate the effect of betaine supplementation on development-related hormones, body composition, and anthropometrics in professional youth soccer players during a competitive season. Twenty-nine players (age, 15.45 ± 0.25 years) were matched based upon position and then randomly assigned to a betaine group (2 g/day; n = 14, BG) or placebo group (PG, n = 15). All subjects participated in team practices, conditioning, and games. If a subject did not participate in a game, a conditioning protocol was used to ensure workload was standardized throughout the 14-week season. Growth hormone (GH), insulin-like growth factor-1 (IGF-1), testosterone, cortisol, height, weight, and body composition were assessed at pre-season (P1), mid-season (P2) and post-season (P3). Anthropometric variables were also measured following a one-year follow-up (F). Significant (p < 0.05) group x time interactions were found for testosterone and testosterone to cortisol ratio (T/C). Both variables were greater in BG at P2 and P3 compared to P1, however, the testosterone was less in the PG at P3 compared to P2. There was no significant group by time interactions for GH, IGF-1, lean body mass, or body fat. There was a significant (p < 0.05) group x time interaction in height and weight at F, with the greater increases in BG compared to PG. Betaine supplementation increased testosterone levels and T/C ratio in youth professional soccer players during a competitive season. Betaine supplementation had no negative effects on growth (height and weight) and may attenuate reductions in testosterone due to intense training during puberty. 



#13 External and internal loads during the competitive season in professional female soccer players according to their playing position: differences between training and competition 

Reference: Res Sports Med. 2021 Mar 4;1-13. doi:0.1080/15438627.2021.1895781. Online ahead of print. 

Authors: Blanca Romero Moraleda, Niels J Nedergaard, Esther Morencos, David Casamichana, Rodrigo Ramirez-Campillo, Jos Vanrenterghem

Summary: The aim of this study was to compare external (EL) and internal loads (IL) during training sessions compared to official matches between elite female soccer players according to their playing position. Training and match data were obtained during the 2017/18 season from eighteen players (age: 26.5±5.7 years; height: 164.4±5.3 cm; body mass: 58.56±5.58 kg) from a first Division Spanish team. The EL (total distance covered; high-speed running distance; number of accelerations and decelerations) was assessed with a Global Positioning System (GPS) and triaxial accelerometer. The IL was assessed with ratings of perceived exertion (RPE; and session-RPE). The EL and the IL from official matches were higher compared to training sessions (p<0.05; effect size [ES]:0.6-5.4). In matches, the EL was greater in Attackers (AT) and Central Midfielders (CM) versus Central Backs (p<0.05; ES:0.21-1.74). During training sessions, the EL was similar between playing positions (p>0.05; ES:0.03-0.87). The EL and the IL are greater in matches compared to training sessions, with greater match-related EL in AT and CM players. Current results may help practitioners to better understand and modulate training session's loads according to playing position, potentially contributing to their performance readiness and injury risk reduction. 



#14 A Sleep Analysis of Elite Female Soccer Players During a Competition Week 

Reference: Int J Sports Physiol Perform. 2021 Mar 3;1-7. doi: 10.1123/ijspp.2020-0706. 

Authors: Craig Thomas, Helen Jones, Craig Whitworth-Turner, Julien Louis 

Summary: The aim was to compare the sleep of female players from a professional soccer team to nonathlete controls across an in-season week and (2) to compare the sleep of core and fringe players from the same team on the night after a match to training nights. Using an observational design, 18 professional female soccer players and 18 female nonathlete controls were monitored for their sleep via wristwatch actigraphy across 1 week. Independent-sample t tests and Mann-Whitney U tests were performed to compare sleep between groups, while an analysis of variance compared sleep on training nights to the night after a match. Soccer players had significantly greater sleep duration than nonathlete controls (+38 min; P = .009; d: 0.92), which may have resulted from an earlier bedtime (-00:31 h:min; P = .047; d: 0.70). The soccer players also had less intraindividual variation in bedtime than nonathletes (-00:08 h:min; P = .023; r: .38). Despite this, sleep-onset latency was significantly longer among soccer players (+8 min; P = .032; d: 0.78). On the night after a match, sleep duration of core players was significantly lower than on training nights (-49 min; P = .010; d: 0.77). In fringe players, there was no significant difference between nights for any sleep characteristic. During the in-season period, sleep duration of professional female soccer players is greater than nonathlete controls. However, the night after a match challenges the sleep of players with more match involvement and warrants priority of sleep hygiene strategies. 



#15 Factors Influencing Creatine Kinase Response in Youth National Team Soccer Players 

Reference: Sports Health. 2021 Mar 4;1941738121999387. doi: 10.1177/1941738121999387.

Authors: Gabor Schuth, Gyorgy Szigeti, Gergely Dobreff, Peter Revisnyei, Alija Pasic, Laszlo Toka, Tim Gabbett, Gabor Pavlik

Summary: Previous studies have examined the relationship between external training load and creatine kinase (CK) response after soccer matches in adults. This study aimed to build training- and match-specific CK prediction models for elite youth national team soccer players. Training and match load will have different effects on the CK response of elite youth soccer players, and there will be position-specific differences in the most influential external and internal load parameters on the CK response. Forty-one U16-U17 youth national team soccer players were measured over an 18-month period. Training and match load were monitored with global positioning system devices. Individual CK values were measured from whole blood every morning in training camps. The dataset consisted of 1563 data points. Clustered prediction models were used to examine the relationship between external/internal load and consecutive CK changes. Clusters were built based on the playing position and activity type. The performance of the linear regression models was described by the R2 and the root-mean-square error (RMSE, U/L for CK values). The prediction models fitted similarly during games and training sessions (R2 = 0.38-0.88 vs 0.6-0.77), but there were large differences based on playing positions. In contrast, the accuracy of the models was better during training sessions (RMSE = 81-135 vs 79-209 U/L). Position-specific differences were also found in the external and internal load parameters, which best explained the CK changes. The relationship between external/internal load parameters and CK changes are position specific and might depend on the type of session (training or match). Morning CK values also contributed to the next day's CK values. The relationship between position-specific external/internal load and CK changes can be used to individualize postmatch recovery strategies and weekly training periodization with a view to optimize match performance. 






External Loads in Under-12 Players during Soccer-7, Soccer-8 and Soccer-11 Official Matches

The aim of the study was to compare the external loads (i.e., displacement distances and velocities) of 10–11 years-old soccer players during Soccer-7 (i.e. seven-a-side), Soccer-8 (i.e. eight-a-side) and Soccer-11 (i.e. eleven-a-side) official matches.





Fatigue Induced by Repeated COD in Female Footballer: Impact on Limb Biomechanics and Implications for ACL Injury Prevention

The aim was to assess the extent to which fatigue impact on joints kinematics and kinetics while performing repeated changes of direction (CoDs) in the light of the ACL risk factors.





Latest research in football - week 20 - 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 Vertical Force-velocity Profiling and Relationship to Sprinting in Elite Female Soccer Players

Reference: Int J Sports Med. 2021 Feb 18. doi: 10.1055/a-1345-8917. Online ahead of print. 

Authors: Sarah A Manson, Cody Low, Hayley Legg, Stephen D Patterson, César Meylan 

Summary: Explosive actions are integral to soccer performance and highly influenced by the ability to generate maximal power. The purpose of this study was to investigate the relationship between force-velocity profile, jump performance, acceleration and maximal sprint speed in elite female soccer players. Thirty-nine international female soccer players (24.3±4.7 years) performed 40-m sprints, maximal countermovement jumps and five loaded squat jumps at increasing loads to determine individual force-velocity profiles. Theoretical maximal velocity, theoretical maximal force, maximal power output, one repetition maximal back squat and one repetition maximal back squat relative to body mass were determined using the force-velocity profile. Counter movement jump, squat jump and maximal power output demonstrated moderate to large correlation with acceleration and maximal sprint speed (r=- 0.32 to -0.44 and -0.32 to -0.67 respectively, p<0.05). Theoretical maximal velocity and force, one repetition maximal and relative back squat demonstrated a trivial to small relationship to acceleration and maximal sprint speed (p>0.05). Vertical force-velocity profiling and maximal strength can provide valuable insight into the neuromuscular qualities of an athlete to individualize training, but the ability to produce force, maximal power, and further transference into sprint performance, must be central to program design. 



#2 Psychological Correlates of Insomnia in Professional Soccer Players: An Exploratory Study

Reference: Eur J Sport Sci. 2021 Feb 18;1-20. doi: 10.1080/17461391.2021.1892197. Online ahead of print. 

Authors: Andrea Ballesio, Mariacarolina Vacca, Valeria Bacaro, Adriano Benazzi, Paola De Bartolo, Fabio Alivernini, Fabio Lucidi, Caterina Lombardo, Chiara Baglioni 

Summary: Sleep promotes health, wellbeing, recovery and athletic performance. As a consequence, sleep problems in athletes may have detrimental effects. Previous investigations showed that professional athletes often reported to suffer of poor sleep quality and insomnia (e.g., difficulties falling asleep and/or maintaining sleep). However, psychological variables exacerbating and maintaining insomnia in professional athletes as well as its mechanistic pathways are still largely unknown. Available literature mostly focused on effects of sport-related variables, such as evening training and stimulant consumption on athletes' sleep. Instead, the contribution of cognitive and emotional variables globally associated with insomnia in athletes in clinical models has been largely neglected. To address these limitations, this study explored the associations between emotional experience, pre-sleep arousal, pre-sleep worry and rumination and insomnia severity in a sample of 210 (25.93±6.68 years) male professional soccer players. Bivariate correlations, multiple regression, and structural equation modelling with manifest variables (path analysis) were computed. Results showed that insomnia severity was associated with stimulants consumption, pre-sleep arousal, negative emotions, positive emotions, and pre-sleep worry/rumination (all p < .05). Path analysis showed that relationship between stimulant consumption, emotional experience, worry/rumination and insomnia was mediated by pre-sleep arousal (p < .05). Our results suggest that preventive and interventional studies in professional soccer players would benefit from considering global cognitive-emotional variables as targets of interventions. 



#3 An objective description of routine sleep habits in elite youth football players from the Middle-East

Reference: Sleep Med. 2021 Jan 23;80:96-99. doi: 10.1016/j.sleep.2021.01.029. Online ahead of print. 

Authors: Lorenzo Lolli, Marco Cardinale, Emmanuel Lopez, Mohd Firdaus Maasar, Johannes Marthinussen, Daniele Bonanno, Warren Gregson, Valter Di Salvo

Summary: Adequate sleep is essential to support preparation and recovery processes for training and competition in athletes. A limited number of studies have examined whether adolescents from the Middle-East meet the minimum age-specific recommendations ranging from 8 to 9 h of night sleep based on objective measurements. This study aimed to provide an objective description of routine sleep habits in elite youth football players from the Middle-East. Using wrist-worn actigraphy, we examined objective measures of sleep over a 14-day surveillance period from fifty-nine, male, Middle-Eastern elite youth football players (age range: 12.1 to 16 years). The observed median sleep duration was approximately 5.5 to 6 h during weekdays and 6.5 to 7.5 h over weekend days. Sleep intermissions resulting in two or more periods of sleep accounted for 8% and 17% of the data during weekdays and weekends, respectively. For the first time, we reported an objective quantification of sleep measures indicating that elite youth athletes from the Middle-East do not meet the age-specific sleep recommendations. Integration of sleep tracking into the routine training monitoring process can be valuable to inform decisions relevant to the adoption of potential multidisciplinary interventions to address sleep insufficiency and disorders in youth athletes. 



#4 Comparative external workload analysis based on the new functional classification in cerebral palsy football 7-a-side. A full-season study 

Reference: Res Sports Med. 2021 Feb 12;1-13. doi: 10.1080/15438627.2021.1888105. Online ahead of print. 

Authors: J M Gamonales, J Muñoz-Jiménez, Carlos D Gómez-Carmona, S J Ibáñez 

Summary: The evolution of functional classification (FT) is important for promoting competitive balance. Technological advances allow the objective monitoring of competitive demands that is required to manage and individualize workloads. Therefore, this study aimed to characterize external workload in all matches from the 2018/2019 season of the CPF7 Spanish National League and to compare demands based on the new FT (FT1, FT2 yFT3) in time-motion (locomotion and speed changes) and accelerometer-based workload (impacts). Statistical analysis was composed of one-way ANOVA with Bonferroni post-hoc and omega partial squared effect size. Differences were found among all FT in total distance, running, high-intensity, sprinting, very high accelerations and decelerations (FT3> FT2> FT1; p < .01; ωp 2= 0.29-to-0.43); and with respect to the highest functional limitation (FT3 = FT2> FT1) in maximum sprinting, moderate-high accelerations and decelerations, total impacts and at very-low intensity (ωp 2= 0.13-to-0.29). In conclusion, FT3 players presented a physical advantage with respect to FT2-FT1 players in competition, especially in high-intensity actions that are crucial in team-sports performance. The present results facilitate designing specific training workloads according to FT, players' disability and competition demands, being the first approach to characterize match demands with inertial devices based on the new FT. 



#5 Psychological Parameters in Sub-Elite, Male, Youth Soccer Players with Jumper's Knee Following Physical Therapy Compared to Healthy Controls: A Longitudinal Examination

Reference: Int J Sports Phys Ther. 2021 Feb 1;16(1):114-125. Differences in Physical and 

Authors: Marc Niering, Thomas Muehlbauer 

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Summary: Many adolescent athletes suffer from jumper's knee (JK) over a long period of time and return to sports before symptoms are fully resolved. Current treatment methods may not reduce pain in the short term, especially not during a competitive season. The purpose of this study was to investigate differences in physical, psychological, and injury-/pain-related parameters in sub-elite male youth soccer players, who previously underwent physical therapy for JK compared to healthy controls (HC) over the course of a season. All subjects were tested four times (start of the season [T1], 6 [T2], 16 [T3], and 20 [T4] weeks after the start of the season). Outcome measures included muscle power (drop jump, jump-and-reach), change of direction speed [CODS] (acyclic sprint), speed (tapping, 30-m linear sprint), endurance (Yo-Yo intermittent recovery test level 1), the Achievement Motives Scale (AMS) Sport, and injury-/pain-related data. Univariate analysis of variance was used to compare differences in variables between the two groups over the course of a soccer season. Over the season, the jumper's knee group (JK; 15.1 ± 0.8 yr) demonstrated significantly worse physical performance in CODS (to the left side: 1.37≤ Cohen's d ≤ 1.51 [T1-T4]; p < 0.001 / to the right side: 1.24 ≤ d ≤ 1.53 [T1-T4]; p < 0.001) and speed (0.48 ≤ d ≤ 1.26 [T1-T4]; p < 0.007) compared to healthy controls (HC; 15.0 ± 1.0 yr). Further, psychological parameters showed worse values in JK than in HC for the AMS Sport items "hope for success" and "fear of failure" that especially showed a significant difference at T1 (d = 0.65; p = 0.032 / d = 0.68; p = 0.027) and T2 (d = 0.50; p = 0.076 / d = 0.80; p = 0.012). Moreover, the JK group showed significantly higher incident rates for non-contact lower limb injuries (d = 0.69; p = 0.049) per 1,000 hours (i.e., practices/competitions), injury-related rest periods (d = 2.06; p = 0.043), and pain-related training interruptions (d = 1.35; p < 0.001). The observed findings imply that there are significant differences in physical and psychological performance of youth soccer players after physical therapy for JK compared to HC. When designing rehabilitation and/or training programs, as well as determining the point of return to sport the impact of the injury needs to be taken into account. 



#6 The ACE and ACTN3 polymorphisms in female soccer athletes 

Reference: Genes Environ. 2021 Feb 18;43(1):5. doi: 10.1186/s41021-021-00177-3. 

Authors: Qi Wei

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Summary: We investigated the association of ACE I/D and ACTN3 R577X polymorphisms with the performance of Chinese elite female soccer athletes for the first time. The genotype distributions of ACE I/D and ACTN3 R577X in the athlete group and the control group of Chinese females were evaluated via PCR and compared. VO2max value was tested as per standard protocol. Regarding the distribution of ACE polymorphisms, the genotype frequency was indifferent between the athletes (II 40 %, ID 46.7 %, DD 13.3 %) and the controls (II 42 %, ID 48 %, DD 10 %). No difference in the I/D allele frequency was observed between the athlete group and the control group. Regarding the distribution of ACTN3 polymorphisms, the genotype frequency was significantly different between the athletes (XX 0 %, XR 53.3 %, RR 46.7 %) and the controls (XX 16 %, XR 44 %, RR 40 %). The allele frequency was observed no different between the athlete and the control group. The ACE ID and ACTN3 RR genotype combination was associated with higher VO2max values among defenders than among other players. According to VO2max values,The ACE and ACTN3 genotype combinations (II/ID/DD + RR/XR) significantly differed between the athletes and the controls (p < 0.05). These results suggested that the Chinese elite female soccer athletes were more likely to harbor the I allele and the R allele and that the combination of ACE II/ID and ACTN3 RR/XR was a synergetic determinant of the athletic performance of females in soccer. 



#7 Relationship Between Subjective and External Training Load Variables in Youth Soccer Players 

Reference: Int J Sports Physiol Perform. 2021 Feb 19;1-7. doi: 10.1123/ijspp.2019-0956. Online ahead of print. 

Authors: Patrick C Maughan, Niall G MacFarlane, Paul A Swinton 

Summary: The purpose was to quantify and describe relationships between subjective and external measures of training load in professional youth soccer players. Data from differential ratings of perceived exertion (dRPE) and 7 measures of external training load were collected from 20 professional youth soccer players over a 46-week season. Relationships were described by repeated-measures correlation, principal component analysis, and factor analysis with oblimin rotation. Significant positive (.44 ≤ r ≤ .99; P < .001) within-individual correlations were obtained across dRPE and all external training load measures. Correlation magnitudes were found to decrease when training load variables were expressed per minute. Principal component analysis provided 2 components, which described 83.3% of variance. The first component, which described 72.9% of variance, was heavily loaded by all measures of training load, while the second component, which described 10.4% of the variance, appeared to have a split between objective and subjective measures of volume and intensity. Exploratory factor analysis identified 4 theoretical factors, with correlations between factors ranging from .5 to .8. These factors could be theoretically described as objective volume, subjective volume, objective running, and objective high-intensity measures. Removing dRPE measures from the analysis altered the structure of the model, providing a 3-factor solution. The dRPE measures are significantly correlated with a range of external training load measures and with each other. More in-depth analysis showed that dRPE measures were highly related to each other, suggesting that, in this population, they would provide practitioners with similar information. Further analysis provided characteristic groupings of variables. 



#8 Effects of Different Recovery Times on Internal and External Load During Small-Sided Games in Soccer 

Reference: Sports Health. 2021 Feb 23;1941738121995469. doi: 10.1177/1941738121995469.

Authors: Luis Branquinho, Ricardo Ferraz, Bruno Travassos, Daniel A Marinho, Mário C Marques

Summary: The ability to maintain a high intensity of exercise over several repetitions depends on recovery from previous exercises. This study aimed to identify the effects of different recovery times on internal and external load during small-sided soccer games. An increase in recovery time will increase the external training load and decrease the internal exercise load, which will result in a greater physical impact of the exercise. Twenty male semiprofessional soccer players participated in the present study. They performed the same exercise (5-a-side game format) continuously (1 × 18 minutes) and repeatedly/fractionated (3 × 6 minutes) with different recovery times (30 seconds, 1 minute, 1.5 minutes, and 2 minutes). Their internal load (ie, average heart rate (HR) and maximum HR) and external load (ie, total distance, maximum speed, and ratio meters) were measured using an HR band and an inertial device equipped with a global positioning system, respectively. The manipulation of recovery times induced differences in the internal and external load. For the same total duration, the external and internal load indicators exhibited higher values during the fractionated method, particularly with short recovery periods. The application of small-sided soccer games with different recovery times induced varying responses in training load. To maintain high physical performance and high training load, the fractional method with short recovery periods (ie, 30 seconds) should be used. In contrast, to carefully manage players' efforts and decrease response to training load, continuous or fractional methods with longer recovery periods (ie, 1-2 minutes) should be used. The proper prescription of recovery time between exercises facilitates enhanced training efficiency and optimized performance. 



#9 Impact of COVID-19 Lockdown on Serie A Soccer Players' Physical Qualities 

Reference: Int J Sports Med. 2021 Feb 23. doi: 10.1055/a-1345-9262. Online ahead of print. 

Authors: Ermanno Rampinini, Federico Donghi, Marco Martin, Andrea Bosio, Marco Riggio, Nicola A Maffiuletti

Summary: In March 2020, the COVID-19 pandemic forced most activities in Italy, including soccer, to cease. During lockdown, players could only train at home, with limited evidence regarding the effect of this period. Therefore, this study aimed to investigate the effect of COVID-19 lockdown on professional soccer players' physical performance. Aerobic fitness and vertical jump were assessed before and after four periods in two different seasons: COVID-19 lockdown, competitive period before lockdown, competitive period and summer break of the 2016-2017 season. Linear mixed models were used to examine within-period changes and between-period differences in changes observed during COVID-19 lockdown and the three other periods. Within-period changes in aerobic fitness showed a significant improvement following COVID-19 lockdown (p<0.001) and a significant decline during summer break (p<0.001). Between-period differences were significant in the comparison of COVID-19 lockdown with both the competitive 2019-2020 season (p<0.01) and summer break (p<0.001). For the vertical jump, only the between-period comparison revealed significant differences as the changes associated with COVID-19 lockdown were worse than those of the two competitive periods, for both absolute (p<0.05; p<0.001) and relative peak power (p<0.01; p<0.001). Home-based training during lockdown was effective to improve aerobic fitness, although it did not allow players to maintain their competitive period's power levels. 



#10 Change in dynamic postural control after a training program in collegiate soccer players with unilateral chronic ankle instability 

Reference: J Sports Med Phys Fitness. 2021 Feb 23. doi: 10.23736/S0022-4707.21.11920-6. Online ahead of print. 

Authors: Daichi Sadakuni, Kosuke Takeuchi, Fumiko Tsukuda, Takeshi Komatsu

Summary: Improving dynamic postural stability after lateral ankle sprain due to chronic ankle instability helps prevent recurrence, and changes in dynamic postural stability can be assessed with the Star Excursion Balance Test. To date, no studies have examined the change in Star Excursion Balance Test score after the end of a balance training program or whether chronic ankle instability affects the rate of change. To examine the effect of chronic ankle instability on changes in Star Excursion Balance Test. score over time after a balance training program. Fifteen collegiate soccer players with chronic ankle instability selected with the Cumberland Ankle Instability Tool and ultrasonography. Participants completed a 6-week balance training program. We assessed the Star Excursion Balance Test 5 times (before and immediately after the program and 2, 4, and 6 weeks later) and examined differences in the duration of training effects by a 2-way analysis of variance, with Bonferroni correction for post hoc comparisons to explain any significant interactions. The significance level for all analyses was set at P < .05. We performed statistical analyses with SPSS version 25. Analysis of the posterolateral and posteromedial scores in Star Excursion Balance Test showed a significant effect of time. Post hoc analysis of the posterolateral score showed that for each leg, participants reached significantly farther after the program than before (P = .012). The posterolateral scores at 2, 4, and 6 weeks after the training program did not differ from before the program, but the posteromedial score was significantly improved immediately after the program (P = .008) and also 2 (P = .004) and 4 weeks later (P = .006). A 6-week balance training program to improve dynamic postural control can improve posterolateral and posteromedial scores in people with chronic ankle instability, and the improvements in posteromedial are still present 4 weeks after program completion. 



#11 Concordance between the weight of Spanish adolescent soccer players, their self-perceived weight, and their weight as perceived by their parents 

Reference: J Pediatr Nurs. 2021 Feb 20;S0882-5963(21)00052-X. doi: 10.1016/j.pedn.2021.02.011. 

Authors: María Del Mar Fernández-Álvarez, Rubén Martín-Payo, Edurne Zabaleta-Del-Olmo, Rebeca García-García, Xana González-Méndez, Sergio Carrasco-Santos

Summary: In the context of soccer clubs, to analyze the concordance between players' actual weight, their self-perceived weight, and their weight as perceived by their parents; to determine which variables might explain the presence of concordance between parents' perception of adolescents' weight and their actual weight. Design and study: A cross-sectional study involving 330 soccer players aged between 13 and 16. Data on personal characteristics of adolescents and parents were analyzed, as well as parents' perceptions of adolescents' weight status and their self-perception. A descriptive analysis of the personal characteristics of the sample (adolescents and parents) and an analysis of the variables explaining the presence of concordance between the parents' perception of adolescents' weight and their actual weight were performed. 19% of the adolescents were overweight and 3.4% were obese. The concordance between parents' perceptions of players' weight and players' actual weight was weak. The concordance between adolescents' self-perceived weight and their actual weight was moderate. The difference in BMI scores according to presence or absence of concordance was statistically significant: these scores were higher in the absence of concordance. Discordance between adolescents' weight and their parents' perception of their weight was associated with parents having lower levels of education. A high percentage of parents and players misperceived their actual weight. This discrepancy was associated with higher BMI scores for adolescents. Nurses should include promotion of accurate weight perception in educational interventions on excess weight. 



#12 The influence of training status on right ventricular morphology and segmental strain in elite pre-adolescent soccer players 

Reference: Eur J Appl Physiol. 2021 Feb 22. doi: 10.1007/s00421-021-04634-3. Online ahead of print. 

Authors: Viswanath B Unnithan, Alexander Beaumont, Thomas W Rowland, Nicholas Sculthorpe, Keith George, Rachel Lord, David Oxborough

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Summary: Cardiac modifications to training are a product of the genetic pre-disposition for adaptation and the repetitive haemodynamic loads that are placed on the myocardium. Elite pre-adolescent athletes are exposed to high-intensity training at a young age with little understanding of the physiological and clinical consequences. It is unclear how right ventricular (RV) structure and function may respond to this type of stimulus. The aim of this study was to compare RV structure and strain across the cardiac cycle and within individual segments in elite soccer players (SP) and controls (CON). Twenty-two highly trained, male pre-adolescent SP and 22 age-and sex-matched recreationally active individuals CON were investigated using 2D echocardiography, including myocardial speckle tracking to assess basal, mid-wall, apical and global longitudinal strain and strain rate during systole (SRS) and diastole (SRE and SRA). greater RV cavity size was identified in the SP compared to CON (RVD1 SP: 32.3 ± 3.1 vs. CON: 29.6 ± 2.8 (mm/m2)0.5; p = 0.005). No inter-group differences were noted for peak global RV strain (SP: - 28.6 ± 4.9 vs CON: - 30.3 ± 4.0%, p = 0.11). Lower mid-wall strain was demonstrated in the SP compared to CON (SP: - 27.9 ± 5.8 vs. CON: - 32.2 ± 4.4%, p = 0.007). Soccer training has the potential to increase RV size in pre-adolescent players. The unique segmental analyses used in this study have identified inter-group differences that were masked by global strain evaluations. The clinical and physiological implications of these findings warrant further investigation. 



#13 Asymptomatic Foot and Ankle Abnormalities in Elite Professional Soccer Players 

Reference: Orthop J Sports Med. 2021 Jan 29;9(1):2325967120979994. doi: 10.1177/2325967120979994. eCollection 2021 Jan. 

Authors: Eduard Bezuglov, Vladimir Khaitin, Artemii Lazarev, Alesia Brodskaia, Anastasiya Lyubushkina, Kamila Kubacheva, Zbigniew Waśkiewicz, Arseniy Petrov , Nicola Maffulli 

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Summary: Professional soccer players are often evaluated with asymptomatic lesions of the ankle and foot, and such abnormalities may eventually become clinically relevant. The purpose was to ascertain the prevalence of foot and ankle abnormalities in elite professional adult soccer players. Professional adult male elite soccer players (n = 37) underwent magnetic resonance imaging (MRI) scans of both their feet and ankles. All competed for their respective national junior or adult soccer teams. MRI scans were performed with 1.5-T scanners and analyzed independently by 2 experienced radiologists. The MRI scans of 86.5% of the players showed degenerative joint disease (DJD) in at least 1 of the joints of the foot and ankle. Articular cartilage lesions in the joints of the foot and ankle were evident in 42% of the scans. Of all lesions, 17% were grade 3 or 4 (Noyes and Stabler classification) cartilage lesions and accompanied by subchondral bone marrow edema. The greater the age, weight, and height of the players, the greater was the odds ratio of DJD of the ankle joint. Synovitis in at least 1 of the joints of the foot was detected in 64% of the MRI scans. Leg dominance significantly correlated with bone marrow edema of the talus. Elite professional soccer players are often evaluated with a high prevalence of asymptomatic osteochondral lesions with subchondral bone marrow edema in the foot and ankle. These osteochondral lesions may remain asymptomatic or, with the continuing high-intensity stresses that modern professional soccer demands of its athletes, may evolve and cause foot and ankle pain. It is unclear whether and which interventions can be implemented to prevent the occurrence of these abnormalities in the first place. 






Quantifying and Comparing the Match Demands of U18, U23 and 1ST Team English Professional Soccer Players

The aim of this study was to quantify and compare the match load demands of U18, U23, and 1ST team players during the official season.





How to improve technical and tactical actions of dominant and non-dominant players in children’s football?

As young football players develop important technical and tactical skills during competitive matches, this study investigated quantity and quality of technical and tactical actions in real game conditions in a 4v4 compared to the traditional 7v7 match format.





Latest research in football - week 19 - 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 Performing more than 20 purposeful gameplay headers in a soccer season may alter autonomic function in female youth soccer players 

Reference: Res Sports Med. 2021 Feb 17;1-9. doi: 10.1080/15438627.2021.1888098. Online ahead of print. 

Authors: Marquise M Bonn, Alexandra B Harriss, James W G Thompson, James P Dickey 

Summary: This study evaluated the effects of cumulative purposeful soccer heading on autonomic nervous system function in 22 female youth soccer players (13.3 ± 0.9 years). A 10 minute electrocardiogram recording was collected at baseline and following the 20 game season (post-season) to calculate measures of heart rate variability (HRV), including standard deviation of the normal-normal intervals, total power, high frequency (HF), low frequency (LF), LF:HF, normalized HF and normalized LF. Participants were categorized into low- (<20 headers per season; n = 13) and high- (>20 headers per season; n = 9) exposure groups. Mann-Whitney U tests demonstrated no significant differences between groups for any HRV metric. However, the increased normalized LF power (low exposure 8.67 and high exposure -31.17, respectively; r = 0.35) and LF:HF power (-6.39 and 15.80, respectively; r = 0.35), between groups had moderate practical significance. Therefore, female youth players who perform more than 20 purposeful headers during a soccer season may exhibit altered autonomic function. 



#2 Short-Term Psychological and Hormonal Effects of Virtual Reality Training on Chronic Low Back Pain in Soccer Players

Reference: J Sport Rehabil. 2021 Feb 16;1-10. doi: 10.1123/jsr.2020-0075. Online ahead of print. 

Authors: Gopal Nambi, Walid Kamal Abdelbasset, Saud F Alsubaie, Ayman K Saleh, Anju Verma, Mohamed A Abdelaziz, Abdulaziz A Alkathiry 

Summary: The aim was to find the short-term psychological and hormonal effects of virtual reality training on chronic low back pain in American soccer players. The 3-block random sampling method was used on 54 university American soccer players with chronic low back pain, and they were allocated into 3 groups: virtual reality training (VRT; n = 18), combined physical rehabilitation (n = 18), and control (n = 18) groups at University Hospital. They underwent different balance training exercises for 4 weeks. The participants and the therapist who is assessing the outcomes were blinded. Psychological (pain intensity and kinesiophobia) and hormonal (glucose, insulin, Homeostatic Model Assessment of Insulin Resistance, growth hormone, prolactin, adrenocorticotropic hormone, and cortisol) values were measured at baseline, after 4 weeks, and after 6 months. The baseline demographic, psychological, and hormonal data between the VRT, combined physical rehabilitation, and control groups show no statistical difference (P ≥ .05). Four weeks following training, the VRT group shows more significant changes in pain intensity and kinesiophobia than the combined physical rehabilitation and control groups (P < .001), and the improvement was noted in the 6-month follow-up. All the hormonal variables (glucose, insulin, growth hormone, prolactin, adrenocorticotropic hormone, and cortisol) show significant changes at 4-week training (P < .001), except for the Homeostatic Model Assessment of Insulin Resistance (P = .075) between the 3 groups. At 6-month follow-up glucose, prolactin, adrenocorticotropic hormone, and cortisol show more significant difference in the VRT group than the other 2 groups (P < .001). At the same time, insulin (P = .694), Homeostatic Model Assessment of Insulin Resistance (P = .272), and growth hormone (P = .145) failed to show significant changes between the groups. Training through virtual reality is an effective treatment program when compared with conventional exercise training programs from a psychological and hormonal analysis perspective in American soccer players with chronic low back pain. 



#3 Effects of Plyometric Training with Agility Ladder on Physical Fitness in Youth Soccer Players

Reference: Int J Sports Med. 2021 Feb 16. doi: 10.1055/a-1308-3316. Online ahead of print. 

Authors: Alexis Padrón-Cabo, Miguel Lorenzo-Martínez , Alexandra Pérez-Ferreirós, Pablo B Costa, Ezequiel Rey

Summary: The aim of this study was to assess the effects of plyometric training with an agility ladder on components of physical fitness in youth soccer players. A total of twenty male under-13 soccer players were randomly assigned to a plyometric training group with an agility ladder (n=10) or a control group (n=10). Before and after training intervention linear sprint test (5 m, 10 m, 20 m), vertical jump ability (squat jump, countermovement jump and countermovement jump with arms), agility test, and slalom dribble test were assessed. The plyometric training with agility ladder was applied two times per week over six weeks. Data were analyzed using linear mixed model. The plyometric training group showed significant improvements (p<0.001) from pre-test to post-test in countermovement jump, countermovement jump with arms, and slalom dribble test. In the control group, no significant enhancements were obtained in all performance tests (p>0.05). The between-group analysis showed significant differences in countermovement jump with arms (p=0.03), but no significant differences (p>0.05) were found in squat jump, countermovement jump, sprint, agility test, and slalom dribble test. In conclusion, the short-term plyometric training with agility ladder seems to be ineffective and not time-efficient to improve physical fitness in youth soccer players. However, the interpretation of these results must be understood within the sample size limitations. 



#4 Hamstring Injury Prevention for Elite Soccer Players: A Real-World Prevention Program Showing the Effect of Players' Compliance on the Outcome 

Reference: J Strength Cond Res. 2020 Feb 14. doi: 10.1519/JSC.0000000000003505. Online ahead of print. 

Authors: Souhail Chebbi, Karim Chamari, Nicol Van Dyk, Tim Gabbett, Montassar Tabben 

Summary: The aim of this study was to determine the effect of implementing the Nordic hamstring exercise (NHE) to prevent hamstring injuries in soccer. A professional team was followed by the same medical team during 5 successive seasons (2012/2013 through 2016/2017). During the first and last seasons (2012/2013 and 2016/2017), no hamstring preventive action was implemented. For the seasons 2013/2014, 2014/2015, and 2015/2016, a noncompulsory (few players refusing to participate) NHE prevention program was implemented with accurate recording of the players' training and match exposure and attendance to the prevention sessions. The first 10 weeks of the season were used to progressively increase the volume and intensity of the NHE exercises, and at the end of the season, players were split in low-, moderate-, and high-attendance groups to the prevention sessions. Overall, 35 time-loss hamstring strain injuries were accounted for. The injury incidence was 0.30 per player per season, and the injury rate was 0.95 injury/1000 hour of exposure. A nonstatistically significant higher risk of hamstring injury was observed in the control, low, and moderate attendance groups compared with the high-attendance group. The greatest risk of hamstring injury was observed in the low-attendance group (odds ratio 1.77, confidence interval 0.57-5.47, p = 0.32). Implementing a NHE prevention program has a positive effect on the injury rate in a soccer team; however, the compliance of players with such interventions may be critical for its success. 



#5 Resuming professional football (soccer) during the COVID-19 pandemic in a country with high infection rates: a prospective cohort study 

Reference: Br J Sports Med. 2021 Feb 15;bjsports-2020-103724. doi: 10.1136/bjsports-2020-103724.

Authors: Yorck Olaf Schumacher, Montassar Tabben, Khalid Hassoun, Asmaa Al Marwani, Ibrahim Al Hussein, Peter Coyle, Ahmed Khellil Abbassi, Hani Taleb Ballan, Abdulaziz Al-Kuwari, Karim Chamari, Roald Bahr

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Summary: The risk of viral transmission associated with contact sports such as football (soccer) during the COVID-19 pandemic is unknown. The aim of this study was to describe the infective and immune status of professional football players, team staff and league officials over a truncated football season resumed at the height of the COVID-19 pandemic in a country with high infection rates and to investigate the clinical symptoms related to COVID-19 infection in professional football players. Prospective cohort study of 1337 football players, staff and officials during a truncated football season (9 weeks) with a tailored infection control programme based on preventive measures and regular SARS-CoV-2 PCR swab testing (every 3-5 days) combined with serology testing for immunity (every 4 weeks). Clinical symptoms in positive participants were recorded using a 26-item, Likert-Scale-based scoring system. During the study period, 85 subjects returned positive (cycle threshold (cT) ≤30) or reactive (30<cT<40) PCR tests, of which 36 were players. The infection rate was consistent with that of the general population during the same time period. More than half of infected subjects were asymptomatic, and the remaining had only mild symptoms with no one requiring hospitalisation. Symptom severity was associated with lower cT values. Social contacts and family were the most common sources of infection, and no infection could be traced to training or matches. Of the 36 infected players, 15 presented positive serology during the study period. Football played outdoors involving close contact between athletes represents a limited risk for SARS-CoV-2 infection and severe illness when preventive measures are in place. 



#6 Effect of 10 Weeks of Complex Training on Speed and Power in Academy Soccer Players 

Reference: Int J Sports Physiol Perform. 2021 Feb 14;1-6. doi: 10.1123/ijspp.2020-0139. Online ahead of print. 

Authors: Thomas I Gee, Paul Harsley, Daniel C Bishop 

Summary: This study investigated the effects of complex-paired and reverse-contrast 10-week training programs on sprint, power, and change-of-direction speed performance of elite academy soccer players. Seventeen elite academy soccer players each performed assessments of the 10- and 40-m sprint, Abalakov vertical jump, seated medicine-ball throw, and Arrowhead change-of-direction speed test, both prior to and after a twice-weekly 10-week resistance-training program. The participants were randomly split into 2 groups; the complex-paired training group (CPT, n = 9) performed 4 different complex pairs (heavy-resistance exercises paired with plyometric and Olympic lifting-style exercises), with each pair being interspersed with an 8-minute recovery period in line with recommended guidelines. The comparative group-the reverse-contrast training group (RCT, n = 8)-performed the same exercises; however, all of the plyometric and Olympic lifting exercises preceded the heavy-resistance exercises. Both groups achieved postintervention increases in the seated medicine-ball throw test (CPT +1.8% and RCT +1.6%, P < .05), whereas VJ performance improved only in the CPT group (+3.4%, P = .003). No significant improvements were observed in either the 10- and the 40-m sprint or Arrowhead change-of-direction speed test for either group. The CPT experienced a small but significant within-group improvement in jump performance. However, no significant between-groups differences were observed in any of the testing variables postintervention. Subsequently, for academy soccer athletes, the CPT approach did not produce meaningful benefits to performance compared with a more time-efficient reverse-contrast approach. 



#7 Injuries in elite level male beach soccer players: A prospective three year study

Reference: Phys Sportsmed. 2021 Feb 15. doi: 10.1080/00913847.2021.1889933. Online ahead of print. 

Authors: Yavuz Lima, Bulent Bayraktar

Summary: The aim of this study was to investigate the incidence and characteristics of match and training injuries in elite-level national male beach soccer players. The incidence, mechanism, location, type, severity, and burden of injuries of the Turkish national beach soccer team were recorded between 2017-2019. A total of 136 injuries occurred during the study period. Total injury incidence was 238.9 injuries/1,000 match hours (MHs) and 37.7 injuries/1,000 training hours (THs) (p<0.001). Twenty-seven injuries led to time-loss, and the incidences for match and training injuries were 36.7 and 7.9 per 1,000 hours, respectively. Of medical attention injuries (MAI) caused by trauma, 54.6% (n=53) were due to another player and, 60.9% (n=14) of time-loss injuries (TLI) caused by trauma were due to non-contact trauma (p<0.001). While 82% (n=91) of training injuries occurred in lower extremities, 29% (n=9) of match injuries occurred in the head/neck region (p<0.001). Head injury incidence was 45.9 per 1,000 match hours. Of MAI, 50% (n=57) were contusion, and 32.1% (n=9) of TLI were strain (p<0.001). Also, the most common injury subtype was foot/toe contusion during match and training (19.4%; n=6, 27.9%; n=31, respectively). The majority of injuries 91.9% (n=125) had slight severity. Head trauma, tendon injury and foot/toe contusion are important for clinical practice in beach soccer. Protective measures (rule regulation, use of protective equipment, etc.) should be considered to prevent these injuries. 



#8 Bone Mineral Density Differences Across Female Olympic Lifters, Power Lifters, and Soccer Players 

Reference: J Strength Cond Res. 2021 Mar 1;35(3):638-643. doi: 10.1519/JSC.0000000000003944. 

Authors: Woohyoung Jeon, John Michael Harrison, Philip R Stanforth, Lisa Griffin 

Summary: Athletic training improves bone mineral density (BMD) through repeated mechanical loading. The location, intensity, and direction of applied mechanical pressure play an important role in determining BMD, making some sports more advantageous at improving BMD at specific regions. Thirty-seven (10 power lifters [PL], 8 Olympic lifters [OL], 8 soccer players [SP], and 11 recreationally active [RA]) women participated in a cross-sectional study. We measured lumbar spine (L1-L4), femoral neck, total-body BMD, and overall body composition (total fat mass, lean mass, percent body fat) with dual-energy x-ray absorptiometry. All athletic groups had greater total BMD than RA (p = 0.01 [PL]; p < 0.001 [OL]; p = 0.01 [SP]). Olympic lifters had the highest total BMD than all other athletic groups. Olympic lifters had the significantly greater total BMD than PL (p = 0.018), but there was no difference in total BMD between PL and SP. As compared with RA, OL showed greater BMD at both the total lumbar spine (p = 0.002) and the femoral neck (p = 0.007), whereas PL showed greater BMD only for the total lumbar spine (p = 0.019) and SP showed greater BMD only for the femoral neck (p = 0.002). Olympic-style lifting includes both high-impact and odd-impact loading modalities that are associated with the highest BMD at both the lumbar spine and femoral neck. 



#9 Specific physical performances among male elite youth soccer players: effect of maturity status

Reference: J Sports Med Phys Fitness. 2021 Feb 15. doi: 10.23736/S0022-4707.21.11766-9. Online ahead of print. 

Authors: Mohamed Tounsi, Chirine Aouichaoui, Zouhair Tabka, Yassine Trabelsi

Summary: There is a lack of studies that investigated the relationship between anthropometric profile, biological maturity and specific soccer performances. Therefore, the aims of the present study were to establish normative data of anthropometric and specific physical performances and to determine the impact age and somatic maturation on young soccer players (U13-U19, n=487). Measurements include anthropometric variables to determine the age of peak height velocity (PHV), leg muscle volume (LMV) and soccer specific test (SST); Squat jump (SJ), Counter Movement jump (CMJ), sprint 10 meter (T10m), sprint 20 meter (T20m), sprint 30 meter (T30m) and intermittent-endurance tests (YYIRT-L1). Reference values showed a significant difference between anthropometric variables, LMV and SST according to PHV categories. (M)ANOVA analysis showed a significant age using maturity interaction effect of all anthropometric variables. A significant result was reported in the majority of SST performances for the age, the T10m and for T20m performances. The full model of multiple regressions and the multiple equations was used to determine the best predictors of physical performances according to anthropometric variables. This study provides normative data for anthropometric characteristics and physical performances according to chronological age (U13-U19) and maturity groups of young soccer players. 



#10 Injury analysis of a professional female soccer team in first division Italian season 

Reference: J Sports Med Phys Fitness. 2021 Feb 15. doi: 10.23736/S0022-4707.21.11688-3. Online ahead of print. 

Authors: Andrea Pellegrini, Martina Lombardi, Nicola Riva, Franco Combi, Claudio Pecci, Giuseppe Porcellini

Summary: Soccer, the most popular sport worldwide, has seen an exponential increase in women's participation at the elite level in the last few years. The main purpose of the current epidemiological study was to analyze the injury incidence, characteristics, and burden among elite female soccer players during a regular season. We recorded all injuries that occurred throughout the 2018-2019 competitive soccer season (August-April). The studied group consisted of 22 elite players, who were militant in the first national leagues from the first team of the same soccer club in the north of Italy. The 2006 FIFA consensus statement was used to design the injury registration form. Throughout the 2018-2019 season, medical staff treated 35 injuries in 22 females. Of the total number of injuries reported in 9 months (5.8 injuries per 1000 hours of exposure), 7 (20%) occurred during matches and 28 (80%) during training sessions. The most common injury was represented by muscular disorders (18; 51.43%) which affected the thigh in 16 cases, and the lower leg and trunk in one case each. According to an anatomic site, most injuries occurred in the lower limbs (94,28%), with the majority affecting thighs (16; 45%), ankles (8; 23%), and knees (5; 14%). Non-contact injuries are shown to be more frequent than contact injuries, which may be connected to the increasing athletic burden among athletes. Further prospective investigations are needed with a focus on prevention protocols. 



#11 Does aerobic performance define match running performance among professional soccer players? A position-specific analysis 

Reference: Res Sports Med. 2021 Feb 14;1-13. doi: 10.1080/15438627.2021.1888107. Online ahead of print. 

Authors: Toni Modric, Sime Versic, Damir Sekulic

Summary: Aerobic performance is considered an important determinant of match running performance in soccer, but studies have rarely investigated this issue in top-level players. This study examined the possible associations between direct measures of aerobic performance and match running performance in elite soccer players. Aerobic performance was tested at the beginning of the season in laboratory settings. The match-running performance was measured by a global positioning system over a competitive half-season for a total of 82 match performances in professional players from Croatia (age: 23.76 ± 2.64; body height: 181.62 ± 7.09 cm; body mass: 77.01 ± 6.34 kg) and clustered as central player (n = 57) and side player (n = 25) performance. No significant differences in aerobic performance were noted between central and side players. The anaerobic threshold was correlated with high-speed running (19.8-25.1 km/h), sprint running (>25.1 km/h), and high-intensity running (>19.8 km/h) among side players (r = 0.52, 0.53, and 0.59, respectively; p < 0.01). For central players, the aerobic threshold was correlated with the total distance covered, low-intensity running (<14.3 km/h), and distance covered in the zone of running (14.4-19.7 km/h) (r = 0.47, 0.49, and 0.39; p < 0.01, 0.01, and 0.03, respectively). Conditioning for central players should include activities with intensities corresponding to aerobic thresholds, while conditioning of side players should be focused on the development of anaerobic thresholds. 



#12 "He's Just a Wee Laddie": The Relative Age Effect in Male Scottish Soccer 

Reference: Front Psychol. 2021 Jan 28;12:633469. doi: 10.3389/fpsyg.2021.633469. eCollection 2021. 

Authors: James H Dugdale, Allistair P McRobert, Viswanath B Unnithan

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Summary: Significant structural, developmental, and financial constraints exist in Scottish soccer that may predicate a different approach to talent identification and development. To our knowledge, no published reports exist evaluating the prevalence of the relative age effect (RAE) in Scottish soccer players. Consequently, the aim of this study was to investigate the prevalence of the RAE among varied playing levels and ages of male Scottish youth soccer players. Birthdates of male youth players (n = 1,230) from U10 to U17 age groups and from playing levels: "Amateur" (n = 482), "Development" (n = 214), and "Performance" (n = 534), alongside a group of male Scottish senior professional players (n = 261) were recorded and categorized into quartiles (Q1 = January-March; Q2 = April-June; Q3 = July-September; and Q4 = October-December) and semesters (S1 = January-June and S2 = July-December) from the start of the selection year. Birthdates were analyzed for: (a) each playing level and (b) each age group irrespective of playing level. For the varied playing levels examined, an RAE was evident in "Development" and "Performance" playing levels only at youth level. When examining each age group, an RAE was observed in U12-U17 players only. While there was a slight asymmetry favoring Q1 born senior professional players, the RAE was not present within this group of our sample. Results from our study suggest that a bias in selecting individuals born earlier in the selection year may exist within male soccer academy structures, but not at amateur level. The asymmetry favoring chronologically older players at youth but not professional level questions the efficacy of this (un)conscious bias within male Scottish soccer players. 



#13 Effects of Percutaneous Electrical Nerve Stimulation on Countermovement Jump and Squat Performance Speed in Male Soccer Players: A Pilot Randomized Clinical Trial 

Reference: J Clin Med. 2021 Feb 10;10(4):690. doi: 10.3390/jcm10040690. 

Authors: Gracia María Gallego-Sendarrubias, José Luis Arias-Buría, Edurne Úbeda-D'Ocasar, Juan Pablo Hervás-Pérez, Manuel Antonio Rubio-Palomino, César Fernández-de-Las-Peñas, Juan Antonio Valera-Calero

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Summary: It has been suggested that Percutaneous Electrical Nerve Stimulation (PENS) can increase muscle strength. No previous study has investigated changes in performance in semiprofessional soccer players. This study compares the effects of adding two sessions of PENS to a training program versus the single training program over sport performance attributes (e.g., jump height and squat speed) in healthy soccer players. A cluster-randomized controlled trial was conducted on twenty-three semiprofessional soccer players who were randomized into an experimental (PENS + training program) or control (single training program) group. The training program consisted of endurance and strength exercises separated by 15-min recovery period, three times/week. The experimental group received two single sessions of PENS one-week apart. Flight time and vertical jump height during the countermovement jump and squat performance speed were assessed before and after each session, and 30 days after the last session. Male soccer players receiving the PENS intervention before the training session experienced greater increases in the flight time, and therefore, in vertical jump height, after both sessions, but not one month after than those who did not receive the PENS intervention (F = 4.289, p = 0.003, η 2 p: 0.170). Similarly, soccer players receiving the PENS intervention experienced a greater increase in the squat performance speed after the second session, but not after the first session or one month after (F = 7.947, p < 0.001, η 2 p: 0.275). Adding two sessions of ultrasound-guided PENS before a training strength program improves countermovement jump and squat performance speed in soccer players. 



#14 The effects of home confinement on physical activity level and mental status in professional football players during COVID-19 outbreak 

Reference: Phys Sportsmed. 2021 Feb 21;1-7. doi: 10.1080/00913847.2021.1888630. Online ahead of print. 

Authors: Gürhan Dönmez, Ömer Özkan, Yiğitcan Menderes, Şerife Şeyma Torgutalp, Levend Karaçoban, Nevzad Denerel, Savaş Kudaş

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Summary: The coronavirus outbreak caused significant changes in football around the world, such as the suspension of leagues and home isolation of players, etc. The main purpose of the present study was to assess the psychological impacts of lockdown and similar restrictions on professional football players during the coronavirus pandemic. The players from 36 professional football teams (n = 977) among Turkish Super League and First League teams were invited to complete a questionnaire including the Center for Epidemiologic Studies Depression Scale (CES-D), Impact of Event Scale-Revised Scores (IES-R) and short form of International Physical Activity Questionnaire (IPAQ). The online survey was completed by 237 players (24.3%). The mean number of self-quarantine day of participants was 26.9 ± 6.2 days. The median CES-D Scale and IES-R scores were 6.0 (min:0, max:42) and 23.0 (min:0, max:59), respectively. IPAQ scores of the players showed that four-fifths of the players still maintain high physical activity levels. There were negative, very weak and significant correlations between CES-D score and being married (r = -0.146, p = 0.024), as well as between CES-D score and IPAQ-Walking (r = -0.189, p = 0.004). A significant positive very weak correlation was observed between CES-D score and self-quarantine days (r = 0.148, p = 0.024). IPAQ-Walking was an independent predictor of CES-D. These findings support that maintaining regular physical activity and routinely exercising in a safe home environment is one of the most important strategies to ensure healthy mental state. 






Injuries in youth football and the relationship to maturation: Analysis of time-loss injuries during four seasons in English male football

The purpose of this prospective cohort study was to investigate the frequency, incidence, and pattern of time-loss injuries in an elite male football academy, exploring injuries in relation to age and maturation status.





In-season training responses and perceived wellbeing and recovery status in professional soccer players

The aim was to describe professional soccer players’ training responses during a competitive season and to investigate the relationship between these responses with wellbeing and recovery indices.





Latest research in football - week 18 - 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 Acute Effects of Match-Play on Neuromuscular and Subjective Recovery and Stress State in Division I Collegiate Female Soccer 

Reference: J Strength Cond Res. 2021 Feb 4. doi: 10.1519/JSC.0000000000003981. Online ahead of print. 

Authors: Ai Ishida, Caleb D Bazyler, Adam L Sayers, Satoshi Mizuguchi, Jeremy A Gentles 

Summary: The purpose of this study was to investigate acute effects of match-play on neuromuscular performance and subjective recovery and stress state and the relationship between training load (TL) and changes in neuromuscular performance in female soccer players. Twelve National Collegiate Athlete Association Division I players participated (20.7 ± 2.3 years; 64.4 ± 7.2 kg; 164.5 ± 6.0 cm) and completed countermovement jump (CMJ) at 0 kg (CMJ0) and 20 kg (CMJ20) and the Short Recovery Stress Scale (SRSS) at 3 hours pre-match (Pre), 12 hours post-match (Post12), and 38 hours post-match (Post38). Countermovement jump variables included body mass, jump height (JH), modified reactive strength index (RSI), peak force (PF), relative PF, eccentric impulse, concentric impulse (CI), peak power (PP), relative PP (RPP), eccentric average PP, and concentric average power (CAP). The SRSS consists of 4 Stress Scales (SSs) and 4 Recovery Scales (RSs). Training loads included total distance, total PlayerLoad, high-speed running, and session ratings of perceived exertion. Significant moderate to large decreases were observed from Pre to Post12 in JH, RSI, CI, PP, RPP, and CAP in CMJ0 and CMJ20 (p < 0.05, effect size [ES] = 0.63-1.35). Significant changes were observed from Pre to Post12 in all RSs (p < 0.05, ES = 0.65-0.79) and 3 SSs (p < 0.05, ES = 0.71-0.77). Significant correlations were observed between CMJ20 PP from Pre to Post12 and all TLs (p < 0.05, r = -0.58 to -0.68). CMJ0 and CMJ20 JH and PP may indicate acute neuromuscular changes after match-play. The magnitude of CMJ20 PP decrements from Pre to Post12 may be affected by soccer match-play volumes. 



#2 Cardiovascular effects of COVID-19 lockdown in professional Football players 

Reference: Panminerva Med. 2021 Feb 10. doi: 10.23736/S0031-0808.21.04340-8. Online ahead of print. 

Authors: Elena Cavarretta, Ilaria D'Angeli, Maura Giammarinaro, Salvatore Gervasi, Maurizio Fanchini, Andrea Causarano, Vincenzo Costa, Massimo Manara, Noemi Terribili, Luigi Sciarra, Leonardo CalÒ, Chiara Fossati, Mariangela Peruzzi, Francesco Versaci, Roberto Carnevale, Giuseppe Biondi-Zoccai, Giacomo Frati 

Summary: The COVID-19 pandemic with the stay-at-home orders and lockdown has dramatically forced athletes to stop team training and competitions, causing deep changes in habits and lifestyle. Aim of this study was to evaluate in a retrospective single center study the cardiovascular (CV) health and fitness of elite football player after COVID-19 lockdown in Italy and to compare such findings with the 2019 off-season period, in order to identify potential differences in the CV features and outcomes. All 29 professional Football players of the first male team were enrolled before resuming training and competition after COVID-19 lockdown and underwent several exams including physical examination, resting and stress electrocardiography (ECG), echocardiography, spirometry and blood tests. Median age was 27 years (23; 31), with no athlete being COVID-19 positive at the time of the evaluation. In comparison with the usual off-season 2-month detraining, significant differences were found for left ventricular (LV) mass (189g [172; 212] vs. 181g [167; 206], p=0.024) and LV mass index for body surface area (94g/m2 [85; 104] vs 88g/m2 [79.5; 101.5], p=0.017), while LV mass/fat free mass remained unchanged (2.8 g/Kg [2.6; 2.9] vs 2.9 g/Kg [2.6; 3.2], p=0.222). Respiratory function and metabolic profile were improved, while no significant changes were found in ECG findings, at rest and during exercise. Prolonged abstinence from training and competitions induced by lockdown elicited significant changes in comparison with off-season in parameters ascribable to detraining, as the changes in LV mass, in respiratory function and in metabolic profile. 



#3 Injuries in youth football and the relationship to player maturation: an analysis of time-loss injuries during four seasons in an English elite male football academy 

Reference: Scand J Med Sci Sports. 2021 Feb 9. doi: 10.1111/sms.13933. Online ahead of print. 

Authors: Neil Light, Adam Johnson, Stuart Williams, Neal Smith, Beverley Hale, Kristian Thorborg

Summary: A better insight into injuries in elite youth football may inform prevention strategies. The purpose of this prospective cohort study was to investigate the frequency, incidence and pattern of time-loss injuries in an elite male football academy, exploring injuries in relation to age and maturation status. Across four consecutive playing seasons, playing exposure and injuries to all academy players (U'9 to U'21) were recorded by club medical staff. Maturation status at the time of injury was also calculated for players competing in U'13 to U'16 aged squads. Time-loss injury occurrence and maturation status at time of injury were the main outcome measures. A total of 603 time-loss injuries were recorded, from 190 different players. Playing exposure was 229,317 hours resulting in an overall injury rate of 2.4 p/1000h, ranging from 0.7 p/1000h (U'11) to 4.8 p/1000h (u'21). Most injuries were traumatic in mechanism (73%). The most common injury location was the thigh (23%) and the most common injury type was muscle injury (29%) combining to provide the most common injury diagnosis; thigh muscle injury (17%). In U'13-U'16 players, a higher number of injuries to early-maturing players were observed in U'13-U'14 players, whilst more injuries to U'15-U'16 players occurred when classed as 'on-time' in maturity status. Maturation status did not statistically relate to injury pattern, however knee bone (not-fracture) injuries peaked in U'13 players whilst hip/groin muscle injuries peaked in U'15 players. 



#4 Effect of tDCS on well-being and autonomic function in professional male players after official soccer matches 

Reference: Physiol Behav. 2021 Feb 6;233:113351. doi: 10.1016/j.physbeh.2021.113351. Online ahead of print. 

Authors: Alexandre Moreira, Daniel Gomes da Silva Machado, Luciane Moscaleski, Marom Bikson, Gozde Unal, Paul S Bradley, Abrahão F Baptista, Edgard Morya, Thais Cevada, Lucas Marques, Vinicius Zanetti, Alexandre Hideki Okano

Summary: This study aimed to examine the effect of transcranial direct current stimulation (tDCS) used as a recovery strategy, on heart rate (HR) measures and perceived well-being in 12 male professional soccer players. tDCS was applied in the days after official matches targeting the left dorsolateral prefrontal cortex (DLPFC) with 2 mA for 20 min (F3-F4 montage). Participants were randomly assigned to anodal tDCS (a-tDCS) or sham tDCS sessions. Players completed the Well-Being Questionnaire (WBQ) and performed the Submaximal Running Test (SRT) before and after tDCS. HR during exercise (HRex) was determined during the last 30 s of SRT. HR recovery (HRR) was recorded at 60 s after SRT. The HRR index was calculated from the absolute difference between HRex and HRR. A significant increase was observed for WBQ (effect of time; p<0.001; ηp2=0.417) with no effect for condition or interaction. A decrease in HRR (p = 0.014; ηp2=0.241), and an increase in HRR index were observed (p = 0.045; ηp2=0.168), with no effect for condition or interaction. No change for HRex was evident (p>0.05). These results suggest that a-tDCS over the DLPFC may have a positive effect on enhancing well-being and parasympathetic autonomic markers, which opens up a possibility for testing tDCS as a promising recovery-enhancing strategy targeting the brain in soccer players. The findings suggest that brain areas related to emotional and autonomic control might be involved in these changes with a possible interaction effect of tDCS by placebo-related effects, but more research is needed to verify this effect. 



#5 Growth and Maturity Status of Female Soccer Players: A Narrative Review 

Reference: Int J Environ Res Public Health. 2021 Feb 4;18(4):1448. doi: 10.3390/ijerph18041448. 

Authors: Robert M Malina, Diogo V Martinho, João Valente-Dos-Santos, Manuel J Coelho-E-Silva, Sławomir M Kozieł

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Summary: Reported mean ages, heights and weights of female soccer players aged <19 years in 161 studies spanning the years 1992-2020 were extracted from the literature or calculated from data available to the authors; 35 studies spanning the years 1981-2020 also included an indicator of biological maturation. Heights and weights were plotted relative to U.S. reference data. Preece-Baines Model 1 was fitted to moving averages to estimate ages at peak velocity. Maturity indicators included skeletal age, pubertal status, age at menarche, percentage of predicted adult height and predicted maturity offset. Heights and weights showed negligible secular variation across the time interval. Heights were slightly above or approximated the reference medians through 14 years old and then varied between the medians and 75th percentiles through 18 years old. Weights were above the reference medians from 9 to 18 years old. Mean ages at menarche ranged from 12.7 to 13.0 years. The trend in heights and weights suggested the persistence and/or selection of taller and heavier players during adolescence, while estimated age at peak height velocity (PHV) and ages at menarche were within the range of mean ages in European and North American samples. Data for skeletal and sexual maturity status were limited; predicted maturity offset increased linearly with mean ages and heights at prediction. 



#6 Abdominal Organ Injuries in Youth Soccer: A Case Series and Review of Literature

Reference: Curr Sports Med Rep. 2021 Feb 1;20(2):69-75. doi: 10.1249/JSR.0000000000000785. 

Authors: Sayyar Khakimov, Peter Zaki, Joseph Hess, William Hennrikus

Summary: We describe 13 children who presented to the Penn State Health Milton S. Hershey Medical Center (HMC) with pediatric soccer-related abdominal organ injuries. A review of the Pennsylvania Trauma System Foundation's Trauma Registry was performed between 2001 and 2015 for children with soccer injuries hospitalized at trauma centers across Pennsylvania. Out of 52 children at Hershey Medical Center, 13 suffered abdominal organ injuries. Injuries included the spleen [5], kidney [4], liver [2], and combined organ involvement [2]. All patients presented with abdominal and/or flank pain. All patients with kidney injuries presented with hematuria. All patients presented after a player-to-player (P2P) contact. Nearly all patients (12/13) were treated nonsurgically. Our findings showed that abdominal organ injuries constitute a substantial portion of pediatric soccer injuries requiring hospitalization, with spleen being the organ injured most frequently. Soccer-related abdominal organ injuries should be suspected in players who suffer abdominal and/or flank pain, and/or hematuria after a P2P contact. 



#7 Relationship Between Wellness Index and Internal Training Load in Soccer: Application of a Machine Learning Model

Reference: Int J Sports Physiol Perform. 2021 Feb 9;1-9. doi: 10.1123/ijspp.2020-0093. Online ahead of print. 

Authors: Enrico Perri, Carlo Simonelli, Alessio Rossi, Athos Trecroci, Giampietro Alberti, F Marcello Iaia 

Summary: The aim was to investigate the relationship between the training load (TL = rate of perceived exertion × training time) and wellness index (WI) in soccer. The WI and TL data were recorded from 28 subelite players (age = 20.9 [2.4] y; height = 181.0 [5.8] cm; body mass = 72.0 [4.4] kg) throughout the 2017/2018 season. Predictive models were constructed using a supervised machine learning method that predicts the WI according to the planned TL. The validity of our predictive model was assessed by comparing the classification's accuracy with the one computed from a baseline that randomly assigns a class to an example by respecting the distribution of classes (B1). A higher TL was reported after the games and during match day (MD)-5 and MD-4, while a higher WI was recorded on the following days (MD-6, MD-4, and MD-3, respectively). A significant correlation was reported between daily TL (TLMDi) and WI measured the day after (WIMDi+1) (r = .72, P < .001). Additionally, a similar weekly pattern seems to be repeating itself throughout the season in both TL and WI. Nevertheless, the higher accuracy of ordinal regression (39% [2%]) compared with the results obtained by baseline B1 (21% [1%]) demonstrated that the machine learning approach used in this study can predict the WI according to the TL performed the day before (MD<i). The machine learning technique can be used to predict the WI based on a targeted weekly TL. Such an approach may contribute to enhancing the training-induced adaptations, maximizing the players' readiness and reducing the potential drops in performance associated with poor wellness scores. 



#8 Effectiveness of Abdominal and Gluteus Medius Training in Lumbo-Pelvic Stability and Adductor Strength in Female Soccer Players. A Randomized Controlled Study 

Reference: Int J Environ Res Public Health. 2021 Feb 5;18(4):1528. doi: 10.3390/ijerph18041528. 

Authors: Héctor Guerrero-Tapia, Rodrigo Martín-Baeza, Rubén Cuesta-Barriuso

Summary: Abdominal and lumbo-pelvic stability alterations may be the origin of lower limb injuries, such as adductor pathology in soccer players. Imbalance can be caused by both intrinsic and extrinsic factors. In this randomized controlled trial over 8 weeks, 25 female footballers were randomly allocated to an experimental group (isometric abdominal training and gluteus medius-specific training) or a control group (isometric abdominal training). Evaluations were performed at baseline, at the end of the intervention and after a 4-week follow-up period. The exercise protocol in common for both groups included three exercises: Plank, Lateral plank and Bird dog. Specific exercises for the gluteus medius were: Pelvic drop and Stabilization of the gluteus medius in knee valgus. Outcome measures were lumbar-pelvic stability and adductor strength. After the intervention, there was an increase in lumbo-pelvic stability in both groups, being greater in the control group than in the experimental group (mean differences [MD]: 4.84 vs. MD: 9.58; p < 0.01) with differences in the analysis of repeated measures (p < 0.001), but not in group interaction (p = 0.26). Changes were found in adductor strength in the experimental group (MD: -2.48; p < 0.001 in the left adductor; MD: -1.48; p < 0.01 in right adductor) and control group (MD: -1.68; p < 0.001 in the left adductor; MD: -2.05; p < 0.001 in the right adductor) after the intervention, with differences in the analysis of repeated measures in left (p < 0.001) and right (p < 0.001) adductor strength. An abdominal and gluteal training protocol shows no advantage over a protocol of abdominal training alone for lumbo-pelvic stability and adductor strength, while improvements in both variables are maintained at four weeks follow-up. 



#9 Quantifying and modelling the game speed outputs of English Championship soccer players 

Reference: Res Sports Med. 2021 Feb 10;1-13. doi: 10.1080/15438627.2021.1888108. Online ahead of print. 

Authors: Mark Connor, Dylan Mernagh, Marco Beato

Summary: This study aims to quantify and model the game-speed demands of professional soccer players competing in the English Championship league, to compare the effect of match location and to examine the effect of playing position on game-speed outputs across the season. Twenty-eight male professional soccer players were enrolled. Moving average calculations were applied to the raw GNSS (STATSports) speed data of each player's duration matches (home = 14 and away = 9). Positional groups were centre-back (CB), full-back (FB), centre-midfield (CM), wing-midfield (WM) and centre-forward (CF). The maximum value across each of the moving average window durations was extracted and converted to units of metres per minute. Power-law models were fitted to all observations (R2 = 0.64), home only (R2 = 0.98), and away only (R2 = 0.98). No significant effects are observed in game-speed outputs when home and away games are analysed. Significant differences were seen between the following positional groups; CBvs.CF (d = -0.323), CM (d = -0.530) and FB (d = -0.350). CM displayed positive difference compared to WM (d = 0.614). This study reported power-law model fitted game speed. Players' positional groups have significantly different game-speed demands, which should be considered during match analysis and training periodization. This study found that game speed is not affected by the location of the match. 



#10 Markers of muscle damage and strength performance in professional football (soccer) players during the competitive period 

Reference: Ann Transl Med. 2021 Jan;9(2):113. doi: 10.21037/atm-20-2923. 

Authors: Vladimir Khaitin, Eduard Bezuglov, Artemii Lazarev, Sergey Matveev, Olga Ivanova, Nicola Maffulli, Evgeny Achkasov 

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Summary: The present study investigated the impact of competitive soccer on the short-term changes in isometric strength of the adductor muscle group during the competitive season. In this cohort study we evaluated the association between a serum marker of muscle damage [creatine phosphokinase (CPK)] and isometric strength of the adductor muscles of the hip in 30 professional football players (age: 26.7±2.9 years) during two seasons of the national top-level championship. Serum CPK level was determined the day before the match, 12-20, 36-48, 60-72 h after the match. The maximum voluntary isometric contraction force of the adductor muscles complex was determined immediately after having taken blood samples. There was evidence of a statistically significant positive association between age, body mass index (BMI), percentage of body fat, and muscle strength, and between weight and muscle strength. There was evidence of a statistically significant negative association between the level of CPK and the maximum isometric strength of the adductors of soccer players. Changes in CPK levels were associated with the muscle strength recovery trend (P<0.001). The strength/CPK ratio at different time points had a U-shaped curve. Exercise induced muscle damage significantly affects the strength of the adductor muscle group of professional soccer players during the competitive period. The lower the CPK level, the greater the athletes' strength at a given time point. Also, the greater the decrease in CPK level, the greater the rate of strength restoration. 



#11 Session-to-session variations of internal load during different small-sided games: a study in professional soccer players 

Reference: Res Sports Med. 2021 Feb 11;1-13. doi: 10.1080/15438627.2021.1888103. Online ahead of print. 

Authors: Saeid Younesi, Alireza Rabbani, Filipe Manuel Clemente, Hugo Sarmento, António Figueiredo

Summary: The aim of this study was to analyse variations of internal load across small-sided games (SSG) in professional soccer. Twenty players (mean ± SD; age 28.1 ± 4.6 yo, height 176.7 ± 4.9 cm, weight 72.0 ± 7.8 kg) performed 3v3, 4v4, and 6v6 formats with/without goalkeeper and touch limitations. Each condition was repeated over three sessions and heart rate (HR) measures including average HR (HRavg), Edwards' training impulse (Edwards' TRIMP) and time in red zone (>80% of maximal HR) were recorded. All measures had trivial-to-moderate typical error (TE) and trivial differences were observed within intervals. The HRavg showed less coefficient of variations (0.9% to 1.7%) compared to Edwards'TRIMP . min-1 and red zone.min-1 (2% to 9.7%). A reduction trend in TE was observed when touching limitations or using goalkeepers. Practitioners can use different SSG formats but if the aim is to have less noise at higher intensities, more controlled drills are recommended. 






Perceptual and Biochemical Responses in Relation to Different Match-Day +2 Training Interventions in Soccer Players

The aim of this study was to examine the impact of two different post-match training interventions on the subsequent recovery of perceptual and biochemical parameters after the game.





Effects of Foam Rolling as a Recovery Tool in Professional Players

The aim was to examine the effectiveness of Foam Rolling (FR) (20 minutes on quadriceps, hamstrings adductors, gluteals, and gastrocnemius) and passive recovery (20 minutes passive rest) intervention performed immediately after a training session on Total Quality Recovery (TQR), perceived muscle soreness, jump performance, agility, sprint, and flexibility 24 hours after the training.





Latest research in football - week 17 - 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 Talent Development Environments in Football: Comparing the Top-Five and Bottom-Five-Ranked Football Academies in Norway 

Reference: Int J Environ Res Public Health. 2021 Feb 1;18(3):1321. doi: 10.3390/ijerph18031321. 

Authors: Kristian Gangsø, Nils Petter Aspvik, Ingar Mehus, Rune Høigaard, Stig Arve Sæther

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Summary: The aim of this study was to examine junior-elite football players' perception of their talent development environment by comparing clubs ranked as the top-five and bottom-five in the 2017 Norwegian academy classification. In total, 92 male junior-elite football players recruited from under-19 teams from five professional football club academies took part in the study. The Talent Development Environment Questionnaire (TDEQ-5; Martindale et al. 2010) was used to measure the players' perceptions of their team environment. The subscale long-term development focus and support network had the highest score and indicated that they perceived that the environment was high quality with respect to those factors. Players from the top-five-ranked clubs perceived their development environments to be significantly more positive with respect to holistic quality preparation, alignment of expectations, communication and, compared to players from the bottom-five-ranked clubs. The players' perceptions of the talent development environment seem to be in alignment of the academy classification undertaken by the Norwegian top football association. 



#2 A Longitudinal Exploration of Match Running Performance during a Football Match in the Spanish La Liga: A Four-Season Study 

Reference: Int J Environ Res Public Health. 2021 Jan 28;18(3):1133. doi: 10.3390/ijerph18031133. 

Authors: Eduard Pons, José Carlos Ponce-Bordón, Jesús Díaz-García, Roberto López Del Campo, Ricardo Resta, Xavier Peirau, Tomas García-Calvo

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Summary: This study aimed to analyze and compare the match running performance during official matches across four seasons (2015/2016-2018/2019) in the top two professional leagues of Spanish football. Match running performance data were collected from all matches in the First Spanish Division (Santander; n = 1520) and Second Spanish Division (Smartbank; n = 1848), using the Mediacoach® System. Total distance and distances of 14-21 km·h-1, 21-24 km·h-1, and more than 24 km·h-1, and the number of sprints between 21 and 24 km·h-1 and more than 24 km·h-1 were analyzed. The results showed higher total distances in the First Spanish Division than in the Second Spanish Division (p < 0.001) in all the variables analyzed. Regarding the evolution of both leagues, physical demands decreased more in the First Spanish Division than in the Second Spanish Division. The results showed a decrease in total distance and an increase in the high-intensity distances and number of sprints performed, although a clearer trend is perceived in the First Spanish Division (p < 0.001; p < 0.01, respectively). Knowledge about the evolution of match running performance allows practitioners to manage the training load according to the competition demands to improve players' performances and reduce the injury rate. 



#3 Comparison of Goal Scoring Patterns in "The Big Five" European Football Leagues 

Reference: Front Psychol. 2021 Jan 13;11:619304. doi: 10.3389/fpsyg.2020.619304. eCollection 2020. 

Authors: Chunhua Li, Yangqing Zhao

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Summary: The objective of the study was to compare goal scoring patterns among the "Big Five" European football leagues during the 2009/2010-2018/2019 seasons. A total of 18 pattern dimensions related to the offense pattern, the shooting situation and the scoring time period were evaluated. Kruskal-Wallis analyses revealed significant pattern differences among the five leagues. The Spanish La Liga showed a greater proportion of goals from throw-ins. The English Premier League had a higher tendency to score from corner kicks. The German Bundesliga had the greatest number of goals from counterattacks and indirect free kicks, and the Italian Serie A had the greatest proportion of penalties. Ligue 1's scoring ability is weaker than that of the other leagues, especially Bundesliga. The Bundesliga had an overwhelming advantage in goals scored on big chances with assists, while the Premier League had an advantage in goals scored with assists that were not from big chances. However, the differences among the five leagues in the mean goals scored in the last 15 min and the goals from elaborate attacks and direct free kicks were not statistically significant. These results provide a valuable addition to the knowledge of different goal patterns of each league and allow us to better understand the differences among the leagues. 



#4 Professional football clubs and empirical evidence from the COVID-19 crisis: Time for sport entrepreneurship? 

Reference: Technol Forecast Soc Change. 2021 Apr;165:120572. doi: 10.1016/j.techfore.2021.120572. Epub 2021 Jan 13. 

Authors: Jonas Hammerschmidt, Susanne Durst, Sascha Kraus, Kaisu Puumalainen

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Summary: The coronavirus disease (COVID-19) has spread worldwide in a short period and has developed into one of the biggest public health issues of the last decade. The actions initiated by governments to minimize person-to-person contact have also severely affected professional football clubs (PFCs) in the season 2019/20. Given the role of football in Europe, football clubs gained massive public and political attention during the COVID-19 crisis. Based on an exploratory multiple case study approach involving PFCs from five European football leagues, this study investigates the responses of these clubs to the COVID-19 pandemic. The findings show the relevance of solidarity with certain stakeholders during the pandemic, but also reveal the fragility of PFCs due to their financial structure and underdeveloped managerial and entrepreneurial strategies to cope with the crisis. This study contributes theoretically and empirically to the literature on the entrepreneurial behavior and crisis management of elite sport organizations and illustrates a holistic map of a dense, high solidary stakeholder network. 



#5 Exertional heat illness risk factors and physiological responses of youth football players

Reference: J Sport Health Sci. 2021 Jan;10(1):91-98. doi: 10.1016/j.jshs.2019.03.002. Epub 2019 Mar 7. 

Authors: Susan W Yeargin, John J Dickinson, Dawn M Emerson, Jessica Koller, Toni M Torres-McGehee, Zachary Y Kerr

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Summary: The aim was to determine which intrinsic and extrinsic exertional heat illness (EHI) risk factors exist in youth American football players and observe perceptual and physiological responses of players during events (games and practices). Cross-sectional cohort study observing 63 youth football players, varying in position. Independent variables were league (weight-restricted (WR, n = 27) and age-restricted (AR, n = 36)) and event type. Dependent variables were anthropometrics, work-to-rest ratio, and wet bulb globe temperature. Descriptive variables included preparticipation examination and uniform configuration. A subset of 16 players participated in physiological variables (heart rate and gastrointestinal temperature). Data collection occurred on 7 AR and 8 WR nonconsecutive practices and the first 3 games of the season. Mean values for anthropometric variables were higher (p < 0.05) in the AR league than the WR league. Work time (χ2 (1,111) = 4.232; p = 0.039) and rest time (χ2 (1,111) = 43.41; p < 0.001) were significantly greater for games, but ratios were significantly higher for practices (χ2 (1,111) = 40.62; p < 0.001). The majority of events (77%) observed were in black and red flag wet bulb globe temperature risk categories. A total of 57% of the players had a preparticipation examination, and up to 82% of events observed were in full uniforms. Individual gastrointestinal temperature and heart rate responses ranged widely and no players reached critical thresholds. Extrinsic (disproportionate work ratios, environmental conditions) and intrinsic (higher body mass index) EHI risk factors exist in youth football. Certain risk factors may be influenced by event and league type. National youth football organizations need to create thorough guidelines that address EHI risk factors for local leagues to adopt. 



#6 Analysis of Burnout and Psychosocial Factors in Grassroot Football Referees 

Reference: Int J Environ Res Public Health. 2021 Jan 27;18(3):1111. doi: 10.3390/ijerph18031111. 

Authors: Natalia Orviz-Martínez, María Botey-Fullat, Sergio Arce-García

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Summary: The aim of this paper is to analyze the interrelationships between the burnout and different psychosocial variables to which the grassroots football referee is exposed, in particular, associated with the influence of the environment and the level of verbal and physical aggression. To this end, a questionnaire was developed, consisting of items from the Maslach Burnout Inventory-General Survey(MBI-GS) and various self-constructed items designed to find out these psychosocial variables. First, a study of the structure of the form was carried out. Second, a structural equation model was designed in order to test the causal relationship between the variables under consideration. The results obtained point to the validity of the proposed theoretical model. It is recommended to initiate training programs for this group aimed at strengthening personal coping and social support strategies, which can help minimize the evolution of this syndrome. 



#7 Heart Rate Variability and Physical Demands of In-Season Youth Elite Soccer Players

Reference: Int J Environ Res Public Health. 2021 Feb 3;18(4):1391. doi: 10.3390/ijerph18041391. 

Authors: Javier Sánchez-Sánchez, Javier Botella, Jose Luis Felipe Hernández, Manuel León, Víctor Paredes-Hernández, Enrique Colino, Leonor Gallardo, Jorge García-Unanue

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Summary: Monitoring fatigue and performance is important for adjusting training loads in soccer. Therefore, knowing the status of the player when applying a training stimulus is key to optimizing the players' development. This study aims to evaluate the interaction between internal and external load, during training and matches, in an elite youth soccer team. Seventeen youth players of the highest Spanish category were monitored with GPS devices during training and matches, as well as recording their nocturnal heart rate variability (HRV). We employed a linear mixed model to assess the physical demands between training and matches, and to compare the HRV variables. A higher total distance (+2993.35-5746.56 m; ES = 1.4), distance at high intensity (+641.24-1907 m; ES = 1.5), sprint distance (+350.46-795.05 m; ES = 2.1), number of sprints (+18.38-41.58; ES = 1.9), and number of repeated sprints (+5.91-15.30; ES = 1.7) (all p < 0.001), but not in the number of accelerations, were reported during the matches when compared to the training sessions during the 11 weeks. The analysis of the HRV variables showed no significant differences between the accumulated values during a training week, providing similar results pre-match or post-match (p > 0.05). The LF/HFRATIO showed a negative influence on the total distance ran, distance at high intensity, distance in sprint, number of sprints, and repeated sprint. RRMEAN was positively related to the sprint number. The results of the present study suggest that nocturnal HRV variables are not different between pre-match and post-match. Furthermore, it suggests that LF/HFRATIO and RRMEAN during pre-match can determine the external load that the player will be able to complete during the match. 



#8 Relative Age Effect in Elite German Soccer: Influence of Gender and Competition Level

Reference: Front Psychol. 2021 Jan 7;11:587023. doi: 10.3389/fpsyg.2020.587023. eCollection 2020. 

Authors: Martin Götze, Matthias W Hoppe 

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Summary: The relative age effect (RAE) is associated with (dis)advantages in competitive sports. While the RAE in elite male soccer reveals a skewed birthdate distribution in relation to a certain cut-off date, research of RAE in elite female soccer is affected by small number of samples and conflicting results. The purpose of this study was to investigate the RAE in elite adult German soccer regarding gender and competition level. The sample comprised 680 female and 1,083 male players of the two top German leagues during the 2019/20 season and German national teams (A-Team to Under 19). Differences between the observed and expected birthdate distributions were analyzed using chi-square statistics and effect sizes followed by calculating odds ratios. Results showed a statistically significant RAE with small effect size across all players included for both genders (female players: P < 0.001, W = 0.16, male players: P < 0.001, W = 0.23). The identified RAE was based on an over-representation of players born at the beginning of the year. According to gender and competition level, RAEs were more pronounced in German male soccer. While significant RAEs were found among males in the first two leagues (first league: P < 0.001, W = 0.19, second league: P < 0.001, W = 0.26), the RAE of females was more pronounced in the second league (first league: P = 0.080, W = 0.16, second league: P = 0.002, W = 0.20). The analysis of RAE regarding the national teams revealed a statistically significant RAE with large effect size for only the youngest investigated age group of male players (Under 19: P = 0.022, W = 0.52). Our data show an RAE in female and male German adult soccer, which could be accompanied by a loss of valuable elite players during the youth phase of the career. Consequently, the pool of talented players at the adult level would be limited. 



#9 Feasibility Study of an Educational Intervention to Improve Water Intake in Adolescent Soccer Players: A Two-Arm, Non-Randomized Controlled Cluster Trial

Reference: Int J Environ Res Public Health. 2021 Feb 2;18(3):1339. doi: 10.3390/ijerph18031339. 

Authors: Rubén Martín-Payo, María Del Mar Fernández-Álvarez, Edurne Zabaleta-Del-Olmo, Rebeca García-García, Xana González-Méndez, Sergio Carrasco-Santos

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Summary: This study aimed to assess the feasibility of an educational intervention on hydration behavior in adolescent soccer players. A pilot study of a two-arm, non-randomized controlled cluster trial was conducted. A total of 316 players aged 13-16 agreed to participate. The response variables were the players' participation in the intervention, their perception of the knowledge acquired, the usefulness and the overall assessment of the intervention. Hydration patterns and acquisition of knowledge on hydration behavior were also assessed. The intervention involved two elements: posters and a web app. A total of 259 adolescents completed the study (intervention group (IG) = 131; control group (CG) = 128). 80.6% of the players responded to the survey assessing the feasibility of the intervention. The mean number of correct answers regarding behavior was significantly higher in the IG (3.54; SD = 1.162) than in the CG (2.64; SD = 1.174) (p < 0.001). The water consumption pattern at all the clubs was ad libitum. Of the players, 10% did not drink any water at all during the game. In conclusion, this intervention has been shown to be feasible for implementation with adolescent soccer players. It suggests that hydration guidelines should be informed by personal factors and that ad libitum water consumption should be avoided. 



#10 The Impact of Covid-19 on Women's Experiences of and Through Football in Buenos Aires

Reference: Front Sports Act Living. 2021 Jan 18;2:624055. doi: 10.3389/fspor.2020.624055. eCollection 2020. 

Authors: Juliana Román Lozano, Mónica Santino, David Wood

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Summary: This research report explores the impact of Covid-19 on women's football in Buenos Aires. The suspension of all forms of football in Argentina as part of the country's hard lockdown measures threatens to undo significant gains made in women's football in recent years. By focussing on the experiences of key actors in a feminist Civil Society Organization (CSO) and a newly professional women's team, respectively, we examine what the pandemic has meant for women's football and for women football players at different levels of the game. We also consider the potential impact of the current situation on the future of women's football in Argentina, representative of wider social advances for women in the country. 



#11 Measuring Sports' Perceived Benefits and Aggression-Related Risks: Karate vs. Football

Reference: Front Psychol. 2021 Jan 18;11:625219. doi: 10.3389/fpsyg.2020.625219. eCollection 2020. 

Authors: Teresa Limpo, Sid Tadrist

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Summary: Little is known about people's perceived benefits and risks of sports, despite their role in shaping people's intentions to engage in them. Here, we developed and tested a scale to measure perceived physical, emotional, cognitive, and social benefits as well as aggression-related risks of karate and football. Additionally, we compared these perceptions within and between these two sports, as well as among undergraduates with current/former participation in different types of physical activity (viz., martial artists, team sports players, participants in other types of physical activity, and non-participants). After a literature review, we created a 5-factor scale with 20 items administered to 184 undergraduates, along with questions about physical activity participation. After removing five items, confirmatory factor analyses supported the factor structure of the scale. Factor loadings and reliability indices were acceptable, though less than desirable results were found concerning the average variance extracted of all benefits dimensions and the reliability of the social benefits dimension. Analyses of variance showed that: (a) physical benefits were seen as the salient outcomes of karate and football, though martial artists perceived karate's physical, emotional, and social benefits to the same extent; (b) in comparison to football, karate was perceived to bring more emotional and cognitive benefits and to entail less aggressiveness risks; (c) karate and football perceptions varied as a function of participant's involvement in physical activity. This study presents a promising instrument to gather information on people's perceptions about karate and football, which can be used to foster people's engagement in them. 



#12 Anthropometric and musculoskeletal gender differences in young soccer players

Reference: J Sports Med Phys Fitness. 2021 Feb 8. doi: 10.23736/S0022-4707.21.11617-2. Online ahead of print. 

Authors: Shuji Taketomi, Kohei Kawaguchi, Yuri Mizutani, Ryota Yamagami, Shin Sameshima, Seira Takei, Kenichi Kono, Hiroshi Inui, Sakae Tanaka, Nobuhiko Haga

Summary: This study aimed to clarify potential gender differences across a comprehensive set of anthropometric and musculoskeletal characteristics within a young soccer player population. This study included 227 (121 males and 106 females with mean ages of 19.0 and 17.5 years, respectively) young elite soccer players. Anthropometric measurements were obtained. In addition, general joint laxity tests assessing the wrist, elbow, shoulder, trunk, hip, knee, and ankle were performed. Muscle flexibility tests were performed on the iliopsoas, quadriceps femoris, hamstring, gastrocnemius, and soleus muscles. Moreover, isometric knee extension and flexion strength and isometric hip abduction strength were measured. Single- and double-leg balance tests were also performed. Male soccer players were taller, heavier, and had lower fat mass and percent body fat, and greater skeletal muscle mass and body minerals than female soccer players. Female soccer players had significantly greater laxity in all tests for general joint laxity. Female soccer players demonstrated significantly better hamstring and soleus flexibility than male soccer players but worse iliopsoas flexibility. Consequently, no significant differences were noticed in the quadriceps and gastrocnemius muscles between the male and female soccer players. However, female soccer players demonstrated significantly weaker knee extension and flexion and hip abduction. The hamstring- quadriceps ratio was significantly lower in female soccer players. Although no significant difference exists in the center of pressure excursion in the double-leg balance test between male and female soccer players, female soccer players displayed a significantly lower center of pressure excursion in the single-leg balance test. Young male and female soccer players demonstrate significantly different anthropometric and musculoskeletal profiles. 



#13 Processing visual information in elite junior soccer players: Effects of chronological age and training experience on visual perception, attention, and decision making 

Reference: Eur J Sport Sci. 2021 Feb 8;1-28. doi: 10.1080/17461391.2021.1887366. Online ahead of print. 

Authors: Stefanie Klatt, Nicholas J Smeeton

Summary: Processing information in peripheral vision is an important perceptual-cognitive skill in team sports. The relative contribution of various perceptual-cognitive skills to expertise in sports throughout adolescence has not been investigated in detail yet. The current study examined the effects of chronological age and training experience on perception, attention, and decision making in young soccer players. Sixty-five elite youth players were required to judge different game situations in a decision-making task involving both perceptual (object detection) and attentional (postural feature recognition) skills to perceive player configurations in the visual periphery. In general, performance decreased in the decision-making and feature-recognition tasks with increasing use of peripheral visual field, but not in the object-detection task. Superior performances were found for under 18 years old players compared to under 16 years old players especially in their attentional skills. Higher training experience affected decision-making and attentional performance. Overall, the findings provide insights and implications for training perceptual-cognitive skills in team sports. 



#14 Hand, Wrist, and Forearm Injuries in Male Professional Soccer Players: A Prospective Cohort Study of 558 Team-Seasons From 2001-2002 to 2018-2019 

Reference: Orthop J Sports Med. 2021 Jan 25;9(1):2325967120977091. doi: 10.1177/2325967120977091. eCollection 2021 Jan. 

Authors: Jonny K Andersson, Håkan Bengtsson, Markus Waldén, Jón Karlsson, Jan Ekstrand

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Summary: The literature on upper extremity injuries in professional soccer players is scarce, and further insight into the onset and cause of these injuries as well as potential differences between goalkeepers and outfield players is important. The purpose was to investigate the epidemiology of hand, wrist, and forearm injuries in male professional soccer players between 2001 and 2019. Between the 2001-2002 and 2018-2019 seasons, 120 European male soccer teams were followed prospectively for a varying number of seasons (558 team-seasons in total). Time-loss injuries and player-exposures to training sessions and matches were recorded on an individual basis in 6754 unique players. Injury incidence was reported as the number of injuries per 1000 player-hours, and between-group differences were analyzed using Z statistics and rate ratios (RRs) with 95% CIs. Between-group differences in layoff time were analyzed. In total, 25,462 injuries were recorded, with 238 (0.9%) of these affecting the hand (71.4%; n = 170), wrist (16.8%; n = 40), and forearm (11.8%; n = 28), producing an incidence of 0.065 injuries per 1000 hours. A majority of the injuries were traumatic with an acute onset (98.7%; n = 235). Fractures were the most common injuries recorded (58.8%; n = 140), often involving the metacarpal bones (25.2%; n = 60) and phalanges (10.1%; n = 24). The injury incidence was significantly higher for goalkeepers (115 injuries; 0.265 per 1000 hours) compared with outfield players (123 injuries; 0.038 per 1000 hours) (RR, 7.0 [95% CI, 5.4-9.0]). Goalkeepers also had a significantly longer mean layoff time than outfield players (23 ± 27 vs 15 ± 27 days; P = .016). Injuries to the hand, wrist, and forearm constituted less than 1% of all time-loss injuries in male professional soccer players. Fractures were most common and constituted more than half of all injuries. Goalkeepers had a 7-fold higher incidence and an over 1-week longer mean layoff time compared with outfield players. 



#15 Effects of Complex Training on Sprint, Jump, and Change of Direction Ability of Soccer Players: A Systematic Review and Meta-Analysis 

Reference: Front Psychol. 2021 Jan 22;11:627869. doi: 10.3389/fpsyg.2020.627869. eCollection 2020. 

Authors: Rohit K Thapa, Danny Lum, Jason Moran, Rodrigo Ramirez-Campillo

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Summary: The aim of this meta-analysis was to evaluate the effects of complex training (CT) on sprint, jump, and change of direction (COD) ability among soccer players. After an electronic search, 10 peer-reviewed articles were considered in the meta-analysis. The athletes included in this meta-analysis were amateur to professional level male soccer players (age range, 14-23 years). These studies incorporated CT in soccer players who were compared to a control group. Significant moderate to large improvements were observed in the CT group [sprint: standard mean difference (SMD) = 0.92-1.91; jump: SMD = 0.96-1.58; COD: SMD = 0.97-1.49] when compared to control groups. Subgroup analysis were also conducted based on age, duration, and competitive level. The beneficial effects of CT were greater in players <18 vs. ≥18 years (linear sprinting; SMD = 2.01 vs. -0.13), after ≥8 vs. <8 weeks (jumping and COD; SMD = 1.55-2.01 vs. 0.31-0.64, respectively) and among professional vs. amateur players (linear sprinting and with COD; SMD = 1.53-1.58 vs. 0.08-0.63, respectively). In conclusion, regular soccer training programs may be supplemented with CT to improve sprint, jump, and COD performance. A longer duration of CT (≥8 weeks) seems to be optimal in improving the physical abilities of soccer players. Professional players and <18 years players may benefit more from CT program. 






Skeletal muscle and performance adaptations to high-intensity training in elite male soccer players

This study examined the skeletal muscle and performance responses across two different exercise training modalities (speed endurance runs (SET) vs. small-sided games (SSG)) which are highly applied in soccer training.





In-Season Internal and External Workload Variations between Starters and Non-Starters — A Case Study

The aims of this study were: (a) to describe the in-season variations of training monotony, training strain and acute:chronic workload ratio (ACWR) through session ratings of perceived exertion (s-RPE), total distance and high-speed running (HSR) and (b) to compare those variations starters vs. non-starters.





Latest research in football - week 16 - 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 Epidemiology of Achilles Tendon Rupture in Italian First Division Football (Soccer) Players and Their Performance After Return to Play 

Reference: Clin J Sport Med. 2021 Feb 1. doi: 10.1097/JSM.0000000000000879. Online ahead of print. 

Authors: Alberto Grassi, Silvio Caravelli, Mario Fuiano, Pieter D'Hooghe, Matteo Filippini, Francesco Della Villa, Massimiliano Mosca, Stefano Zaffagnini 

Summary: The aim was to evaluate the epidemiology, incidence rate, incidence proportion, and prevalence of Achilles tendon ruptures (ATRs) in professional footballers and their performance after the injury. Professional male footballers participating in Serie A in 11 consecutive seasons (2008/2009-2018/2019) were screened to identify ATRs through the online football archive Exposure in matches and training was calculated. The number of matches played in the 5 seasons before and after ATRs was obtained, when possible, together with transfers to a different team or participation in lower Divisions. Eleven ATRs were found in 11 footballers with a mean age of 29.8 ± 4.4 years; 72% of ATR involved the nondominant leg; 58% occurred during matches and 42% during training, with no peculiar distribution along the playing season. The overall incidence proportion was 0.17% (0.11% during matches and 0.06% during training). The overall incidence rate was 0.007 injuries per 1000 hours of play (0.051 during matches and 0.003during training; P < 0.0001). All players returned to play soccer after a mean of 170 ± 35 days after ATRs and participated in an official match after a mean of 274 ± 98 days. However, 2 seasons after ATRs, 3 footballers were playing in a lower Division; 1 played less than 10 matches (compared with >25 matches in the 5 seasons before an ATR) and 1 had retired. An overall ATR rate of 0.007 per 1000 hours of soccer play and an incidence proportion of 0.17% were reported. All footballers return to play; however, up to 40% players decreased the level of play by reducing the number of games or participating in a lower Division 2 seasons after an ATR. 



#2 Morphological Changes of the Hip Commonly Associated With Femoroacetabular Impingement Are Not Correlated With Rotational Range of Hip Motion in Elite Soccer Athletes

Reference: Sports Health. 2021 Feb 4;1941738120973662. doi: 10.1177/1941738120973662.  

Authors: André Orlandi Bento, Guilherme Falótico, Keelan Enseki, Ronaldo Alves Cunha, Benno Ejnisman, Gustavo Arliani, Moisés Cohen

Summary: Morphological changes characteristic of femoroacetabular impingement (FAI) are common in soccer players. However, the clinical relevance of such anatomical variations is still not well-defined. We hypothesized that high alpha angle values and/or acetabular retroversion index (ARI) are correlated with rotational range of motion (ROM) of the hip and that there are clinical-radiological diferences between the dominant lower limb (DLL) and nondominant lower limb (NDLL) in professional soccer players. A total of 59 male professional soccer players (average age 25.5 years, range 18-38 years) were evaluated in the preseason. As main outcome measures, we evaluated the alpha angle and the ARI and hip IR and ER ROM with radiographic analysis. The measurements taken on DLL and NDLL were compared and a significant difference was found between the sides in the ER (P = 0.027), where the DLL measures were 1.54° (95% CI, 0.18-2.89) greater than the NDLL. There were no significant differences between the sides in the measures of IR (P > 0.99), total ROM (P = 0.07), alpha angle (P = 0.250), and ARI (P = 0.079). The correlations between the rotation measurements and the alpha angle in each limb were evaluated and the coefficient values showed no correlation; so also between the ARI and rotation measures. Morphological changes of the femur or acetabulum are not correlated with hip IR and ER ROM in male professional soccer players. ER on the dominant side was greater than on the nondominant side. There was no significant difference in the other measurements between sides. In clinical practice, it is common to attribute loss of hip rotational movement to the presence of FAI. This study shows that anatomical FAI may not have a very strong influence on available hip rotational movement in professional soccer athletes. 



#3 Accelerometry-Workload Indices Concerning Different Levels of Participation during Congested Fixture Periods in Professional Soccer: A Pilot Study Conducted over a Full Season

Reference: Int J Environ Res Public Health. 2021 Jan 28;18(3):1137. doi: 10.3390/ijerph18031137. 

Authors: Filipe Manuel Clemente, Rui Silva, Yung-Sheng Chen, Rodrigo Aquino, Gibson Moreira Praça, Julen Castellano, Hadi Nobari, Bruno Mendes, Thomas Rosemann, Beat Knechtle 

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Summary: The aim of this study was to analyze the variations of acute load (AL), acute: chronic workload ratio (ACWR), training monotony (TM), and training strain (TS) of accelerometry-based GPS measures in players who started in three matches (S3M), two matches (S2M), and one match (S1M) during congested weeks. Nineteen elite professional male players from a Portuguese team (age: 26.5 ± 4.3 years) were monitored daily using global positioning systems (GPSs) over a full season (45 weeks). Accelerometry-derived measures of high metabolic load distance (HMLD), high accelerations (HA), and high decelerations (HD) were collected during each training session and match. Seven congested weeks were classified throughout the season, and the participation of each player in matches played during these weeks was codified. The workload indices of AL (classified as ACWR, TM, and TS) were calculated weekly for each player. The AL of HMLD was significantly greater for S2M than S1M (difference = 42%; p = 0.002; d = 0.977) and for S3M than S1M (difference = 44%; p = 0.001; d = 1.231). Similarly, the AL of HA was significantly greater for S2M than S1M (difference = 25%; p = 0.023; d = 0.735). The TM of HD was significantly greater for S2M than S3M (difference = 25%; p = 0.002; d = 0.774). Accelerometry-based measures were dependent on congested fixtures. S2M had the greatest TS values, while S3M had the greatest TM. 



#4 Mortality of Spanish Former Elite Soccer Players and Coaches 

Reference: Int J Sports Med. 2021 Feb 1. doi: 10.1055/a-1308-3116. Online ahead of print. 

Authors: José Carlos Diz, Santiago Iglesias Sueiro, Eva Diz Ferreira, Miguel Adriano Sanchez-Lastra, Carlos Ayán

Summary: We analyzed whether male Spanish elite soccer players live longer than the general population. Secondly, we compared their mortality with a cohort of soccer players who continued working as soccer elite coaches after retirement. Using age and calendar-date adjusted life tables, we analyzed the mortality hazard ratio of 1333 Spanish male players born before 1950, and who played in elite leagues from 1939, compared with the Spanish population. Using Cox proportional hazards model we compared their mortality with a cohort of 413 players who continued as coaches. Players showed significantly lower mortality than the general population, but this advantage decreased with advanced age, disappearing after 80 years. Coaches showed a similar pattern. Comparing players versus coaches, date of birth and years as professional were associated with survival, but debut age and player position were not. Unadjusted median survival time was 79.81 years (IQR 72.37-85.19) for players and 81.8 years (IQR 74.55-86.73) for coaches. Kaplan-Meier estimator adjusted for covariables showed no difference between cohorts (p=0.254). In conclusion, former Spanish male players showed lower mortality than the general population, but this effect disappeared after 80 years of age. Continuing their career as coaches after retirement from playing did not confer major benefits. 



#5 Unilateral vs. bilateral hamstring strength assessments: comparing reliability and inter-limb asymmetries in female soccer players 

Reference: J Sports Sci. 2021 Jan 31;1-8. doi: 10.1080/02640414.2021.1880180. Online ahead of print. 

Authors: Matthew Cuthbert, Paul Comfort, Nicholas Ripley, John J McMahon, Martin Evans, Chris Bishop

Summary: The aims in the present study were to assess reliability for two unilateral and two bilateral field-based hamstring assessments and compare magnitude, direction and agreement of inter-limb asymmetry between tests and sessions. Twenty-nine female soccer players (age: 21.1 ± 4.5 years; height: 169.7 ± 5.8 cm; body mass: 66.2 ± 6.4 kg) performed three repetitions per leg of unilateral isometric 30° and 90° knee flexion (KF) tasks, and three repetitions total for a bilateral 90° isometric KF and Nordic hamstring exercise. Absolute reliability of most methods were acceptable (<10%). Relative reliability within-session was fair to excellent (ICC≥0.784; lower bound 95%CI ≥0.623). Greater variability in between-session relative reliability was observed during the unilateral tests, demonstrating poor to good (ICC = 0.698-0.798; lower bound 95%CI = 0.274-0.638). Bilateral assessments demonstrated similar ranges of poor to excellent (ICC = 0.679-0.963; lower bound 95%CI = 0.231-0.790). Agreement between-session for inter-limb asymmetry identification was slight and fair in the unilateral tests, with moderate to substantial agreement demonstrated in the bilateral. Being the most reliable within- and between-sessions, demonstrating substantial agreement in asymmetry between-sessions, the NHE would be most appropriate to identify inter-limb asymmetry and assess chronic changes in hamstring strength. 



#6 Game Insight Skills as a Predictor of Talent for Youth Soccer Players 

Reference: Front Sports Act Living. 2021 Jan 15;2:609112. doi: 10.3389/fspor.2020.609112. eCollection 2020. 

Authors: Tom de Joode, Drewes J J Tebbes, Geert J P Savelsbergh

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Summary: Perceptual-cognitive skills are found to be important factors for soccer players. The aim of this study was, therefore, to find within-group differences for game insight in an elite group of youth soccer players by means of a Game Insight inDicator (GID). In addition, the prospective value of perceptual-cognitive skills was examined by following the trajectory of the participants. The GID consisted of film clips that show game situations. The task of the players was to predict the trajectory and destination of the ball and move toward the correct position to receive the pass of a teammate. The film clips stopped 80 ms before, at, and 80 ms after the football contact of a teammate. We also sought to validate the GID against game performance. Participants were talented soccer players 11-13 years old and playing at the elite level for their age. Based on eight independent elite-coach judgments, two groups were created: highly talented players (HT) and less talented players (LT). The coach ratings were supported by a significant difference between the two groups based on the objective notational analysis of their game performance in 4 vs. 4 and 11 vs. 11 matches. With respect to the GID, a significant interaction effect for the groups (HT vs. LT) by occlusion time (-80, 0, and +80 ms) was found, showing that the HT performs better than the LT in 0 and +80 ms condition. In addition, GID scores were compared with soccer levels at the mean age of 19 years. Longitudinal data did not show significant differences between elite and sub-elite. Overall, the GID was found to be a valid and useful indicator for players anticipating the ball's trajectory and destination at age 11-13 years but failed to predict the players' level at age 19 years. The latter indicates how difficult it is to predict talent development. 



#7 Change in Soccer Substitutions Rule Due to COVID-19: Why Only Five Substitutions? 

Reference: Front Sports Act Living. 2021 Jan 15;2:588369. doi: 10.3389/fspor.2020.588369. eCollection 2020. 

Authors: Gustavo R Mota, Izabela Aparecida Santos, Moacir Marocolo

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#8 How Does Cognitive Effort Influence the Tactical Behavior of Soccer Players? 

Reference: Percept Mot Skills. 2021 Jan 31;31512521991405. doi: 10.1177/0031512521991405.

Authors: Felippe da S L Cardoso, Tomás García-Calvo, Tomas Patrick, José Afonso, Israel Teoldo

Summary: In the present study, we aimed to investigate the association between soccer players' cognitive effort and their tactical behavior. We assessed 52 young male soccer players from a first division Brazilian club, using FUT-SAT to evaluate tactical behavior efficiency and Mobile Eye Tracking-XG software and a video test protocol to measure pupillary behavior and cognitive effort. Following data collection, statistical analyses were performed using the Kolmogorov-Smirnov normality test, and linear regression. We found a high inverse association between cognitive effort and tactical behavior efficiency; players with less cognitive effort during the task displayed higher values of tactical behavior efficiency on the field. We concluded that sustaining less cognitive effort in game situations helped players realize better tactical behavior and enabled better performance. 



#9 Goalkeeping in the soccer penalty kick: The dive is coordinated to the kicker's non-kicking leg placement, irrespective of time constraints

Reference: Hum Mov Sci. 2021 Jan 29;76:102763. doi: 10.1016/j.humov.2021.102763. Online ahead of print. 

Authors: Ran Zheng, Caroline de Reus, John van der Kamp

Summary: Traditionally, goalkeeping in the soccer penalty kick has been studied using video-based technology, in which goalkeepers watched video footage of penalty kicks and indicated perceived ball direction. By omitting the requirement to actually dive or jump to the ball, these studies overlooked how action capabilities constrain goalkeepers' actions. By contrast, we examined whether goalkeeping in the penalty kick is consistent with affordance-based control, that is, whether goalkeepers guide their dive by taking into account their action capabilities (i.e., the time they need to intercept the ball). To this end, high- and moderate-skilled goalkeepers faced in-situ penalty kicks. Time constraints were manipulated by varying the kicking distance and the kicker's run-up speed. The results showed that goalkeepers of both skills level scaled the lateral dive onset to their action capabilities, but high-skilled goalkeepers acted closer to their maximum action boundary. In doing so, goalkeepers did not take the varying time constraints into account. Instead, high-skilled goalkeepers acted consistent with a strategy in which they coordinated the onset of the dive with the landing of kicker's non-kicking leg next to the ball. Consequently, we only find partial support for affordance-based control. We propose that this is explained by reliable information becoming available (too) late within the spatiotemporal constraints of the penalty kick. 



#10 Assessment of External Load During Matches in Two Consecutive Seasons Using the Mediacoach ® Video Analysis System in a Spanish Professional Soccer Team: Implications for Injury Prevention

Reference: Int J Environ Res Public Health. 2021 Jan 27;18(3):1128. doi: 10.3390/ijerph18031128. 

Authors: Manuel Alcantarilla-Pedrosa, David Álvarez-Santana, Sergio Hernández-Sánchez, Angel Yañez-Álvarez, Manuel Albornoz-Cabello

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Summary: Knowledge of competition loads is a relevant aspect of injury prevention. We aimed to describe the training and match injury incidence and physical demand variables observed during a competition using a multi-camera video analysis system (Mediacoach®) (LaLigaTM, Madrid, Spain) in a professional Spanish soccer team during two consecutive seasons. 30 players (age: 26.07 ± 3.78 years) participated in the study. Physical variables of 74 matches were collected retrospectively. Injury characteristics of both seasons were also collected. Differences in these variables between the two seasons and by player position and correlations between variables were explored. There were statistically significant differences between the two seasons in the total distance traveled and the distance traveled at a high-intensity sprint (p < 0.05). During the two seasons, there was an average of 4.7 ± 2.2 injuries. The total distance traveled was different according to the playing position, and statistically significant correlations were found in the total distance and sprint at a high intensity for certain positions with different injury severity The match performance data recorded by the Mediacoach® system may provide relevant information by player position to technical and medical staff for injury prevention. 



#11 Fluid Balance, Sweat Na + Losses, and Carbohydrate Intake of Elite Male Soccer Players in Response to Low and High Training Intensities in Cool and Hot Environments

Reference: Nutrients. 2021 Jan 27;13(2):401. doi: 10.3390/nu13020401. 

Authors: Ian Rollo, Rebecca K Randell, Lindsay Baker, Javier Yanguas Leyes, Daniel Medina Leal, Antonia Lizarraga, Jordi Mesalles, Asker E Jeukendrup, Lewis J James, James M Carter

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Summary: Hypohydration increases physiological strain and reduces physical and technical soccer performance, but there are limited data on how fluid balance responses change between different types of sessions in professional players. This study investigated sweat and fluid/carbohydrate intake responses in elite male professional soccer players training at low and high intensities in cool and hot environments. Fluid/sodium (Na+) losses and ad-libitum carbohydrate/fluid intake of fourteen elite male soccer players were measured on four occasions: cool (wet bulb globe temperature (WBGT): 15 ± 7 °C, 66 ± 6% relative humidity (RH)) low intensity (rating of perceived exertion (RPE) 2-4, m·min-1 40-46) (CL); cool high intensity (RPE 6-8, m·min-1 82-86) (CH); hot (29 ± 1 °C, 52 ± 7% RH) low intensity (HL); hot high intensity (HH). Exercise involved 65 ± 5 min of soccer-specific training. Before and after exercise, players were weighed in minimal clothing. During training, players had ad libitum access to carbohydrate beverages and water. Sweat [Na+] (mmol·L-1), which was measured by absorbent patches positioned on the thigh, was no different between conditions, CL: 35 ± 9, CH: 38 ± 8, HL: 34 ± 70.17, HH: 38 ± 8 (p = 0.475). Exercise intensity and environmental condition significantly influenced sweat rates (L·h-1), CL: 0.55 ± 0.20, CH: 0.98 ± 0.21, HL: 0.81 ± 0.17, HH: 1.43 ± 0.23 (p =0.001), and percentage dehydration (p < 0.001). Fluid intake was significantly associated with sweat rate (p = 0.019), with no players experiencing hypohydration > 2% of pre-exercise body mass. Carbohydrate intake varied between players (range 0-38 g·h-1), with no difference between conditions. These descriptive data gathered on elite professional players highlight the variation in the hydration status, sweat rate, sweat Na+ losses, and carbohydrate intake in response to training in cool and hot environments and at low and high exercise intensities. 



#12 Injury rates decreased in men's professional football: an 18-year prospective cohort study of almost 12 000 injuries sustained during 1.8 million hours of play 

Reference: Br J Sports Med. 2021 Feb 5;bjsports-2020-103159. doi: 10.1136/bjsports-2020-103159.

Authors: Jan Ekstrand, Armin Spreco, Håkan Bengtsson, Roald Bahr

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Summary: The UEFA Elite Club Injury Study is the largest and longest running injury surveillance programme in football. The aim was to analyse the 18-season time trends in injury rates among male professional football players. 3302 players comprising 49 teams (19 countries) were followed from 2000-2001 through 2018-2019. Team medical staff recorded individual player exposure and time-loss injuries. A total of 11 820 time-loss injuries were recorded during 1 784 281 hours of exposure. Injury incidence fell gradually during the 18-year study period, 3% per season for both training injuries (95% CI 1% to 4% decrease, p=0.002) and match injuries (95% CI 2% to 3% decrease, p<0.001). Ligament injury incidence decreased 5% per season during training (95% CI 3% to 7% decrease, p<0.001) and 4% per season during match play (95% CI 3% to 6% decrease, p<0.001), while the rate of muscle injuries remained constant. The incidence of reinjuries decreased by 5% per season during both training (95% CI 2% to 8% decrease, p=0.001) and matches (95% CI 3% to 7% decrease, p<0.001). Squad availability increased by 0.7% per season for training sessions (95% CI 0.5% to 0.8% increase, p<0.001) and 0.2% per season for matches (95% CI 0.1% to 0.3% increase, p=0.001). Over 18 years: (1) injury incidence decreased in training and matches, (2) reinjury rates decreased, and (3) player availability for training and match play increased. 



#13 Confirmatory Factor Analysis and Validity of the Sexual Harassment Scale in Football Refereeing

Reference: Int J Environ Res Public Health. 2021 Feb 3;18(4):1374. doi: 10.3390/ijerph18041374. 

Authors: Josefa Sánchez, Sara Serrat, Estefanía Castillo, Alberto Nuviala

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Summary: Inequalities between men and women in the workplace are reflected in professional sports, specifically football refereeing. This phenomenon sometimes becomes sexual harassment since it is a stereotypically considered male profession in which women are a minority. To measure that behavior, it is necessary to count on valid and reliable tools. Therefore, the goal of this study was to determine the factorial structure and the discriminant and convergent validity of the 'sexual experiences questionnaire', version of the Department of Defence (SEQ-DoD). Eighty-nine male football referees and ninety-four female football referees, with a mean age of 23.30 ± 4.85 years, participated in this studio conducted questionnaire in Andalusia, Spain. A confirmatory factor analysis was performed using the robust maximum-likelihood estimation method. The goodness of fit was assessed, and the factorial invariance was calculated to determine the stability of the model. Subsequently, the validity was confirmed. The results corroborated the validity and reliability of the questionnaire adapted to the population studied. Therefore, it can be used as a research instrument. 



#14 Characteristics of Cognitive Abilities among Youths Practicing Football 

Reference: Int J Environ Res Public Health. 2021 Feb 3;18(4):1371. doi: 10.3390/ijerph18041371. 

Authors: Wojciech Paśko, Maciej Śliż, Mariusz Paszkowski, Janusz Zieliński, Klementyna Polak, Maciej Huzarski, Krzysztof Przednowek

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Summary: The aim of the study was to assess selected cognitive abilities depending on age, anthropometric parametres, physical fitness and technical skills in the group of young players training football. The study covered a group of 258 young players practicing football (age: 12.1± 2.03), who were divided into 5 age categories (8-9 years old, 10-11 years old, 12-13 years old, 14-15 years old, 16-17 years old). Selected cognitive abilities include: simple reaction time (SIRT), complex reaction time (CHORT), hand-eye coordination (HECOR) and spatial orientation (SPANT). Studies were performed using Test2Drive computer tests. In addition, the level of physical fitness was measured using: The standing long jump, 30 m sprint, 20 m shuttle run test (without and with the ball) and slalom (without and with the ball). The analysis showed a statistically significant relationship between age and cognitive abilities. There was also a statistically significant correlation between fitness tests and reaction time in individual cognitive tests. There were no statistically significant relationships between technical skills and cognitive abilities. The study confirms that age and physical fitness affect the level of cognitive abilities. 



#15 Knowledge and attitude towards hazardous effects of laser pointers among attendees of football matches in Riyadh, Saudi Arabia 

Reference: Saudi J Ophthalmol. 2020 Nov 22;34(1):25-29. doi: 10.4103/1319-4534.301293. eCollection Jan-Mar 2020. 

Authors: Rahaf Altwijri, Suliman A Alsuliman, Latifa Alanazi, Shaikha H Aldossari, Abeer Ahmad, Hassan Al Dhibi, Sulaiman M Alsulaiman

Summary: There has been a recent increase in accidental retinal injuries due to the careless use of handheld laser devices. The scenarios under which these incidents occur suggest a lack of awareness of the sight-threatening hazards of some handheld lasers. This study aimed to assess knowledge of the population to plan awareness programs and establish protective health policies. This observational cross-sectional study used a newly-developed, validated, and pilot-tested questionnaire to survey attendees of football matches in Saudi Arabia between September to October 2018. Five-hundred and sixty-nine attendees were surveyed, and 76% of respondents knew laser pointers were harmful and could damage the eye. However, 73% of respondents did not think that the blue laser was dangerous, indicating poor awareness regarding this particular laser. Only 38% knew which ocular structure is most commonly damaged, and 15.6% did not realize that brief exposure can cause vision loss. Females had better knowledge compared to males. Respondents between 25 and 40 years old, females, and married individuals had the highest levels of a positive attitude. There was no statistically significant difference in the mean knowledge score between those in the medical field and other fields (P = 0.5). There is an inadequate knowledge of protective measures against handheld lasers. However, there's an overall positive attitude towards spreading awareness about this issue. Yet, targeted awareness campaigns are still needed in addition to more strict government laws to prevent importing or using high-powered handheld laser pointers. 






How modifications in goals in small-sided influence the tactical actions of young soccer players

This study analysed the influence of the absence of goalkeeper and the number of goals in tactical actions in 3 configurations of small-sided and conditioned games (SSCGs): (a) goalkeeper + 3 vs. 3 + goalkeeper; (b) 3 vs. 3 (no goalkeeper); and (c) 3 vs. 3 with 2 mini goals.





Visual Search Strategies of Soccer Players Executing a Power vs. Placement Penalty

The current study investigated how the type of penalty kick being taken affected the kicker’s visual search strategy and where the ball hit the goal (end ball location).





Latest research in football - week 15 - 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 Sport-Specific Functional Tests and Related Sport Injury Risk and Occurrences in Junior Basketball and Soccer Athletes

Reference: Biomed Res Int  2020 Dec 11;2020:8750231. doi: 10.1155/2020/8750231. eCollection 2020. 

Authors: Wen-Dien Chang, Chi-Cheng Lu

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Summary: Sport-specific functional tests were used to assess the power, speed, and agility of the lower extremity for a specific sport, but comparison of the differences and association with sport injury was rare. The aim of this study was to investigate the differences in sport-specific functional tests between junior basketball and soccer athletes and analyze the sport injury risk and occurrences. All participants were evaluated using the sprint test, vertical jump (VJ) test, agility T test, and functional movement screen (FMS). There were significant intergroup differences in the sprint test, VJ test, agility T test, and FMS. Specific functional tests were compared against FMS score, either FMS ≤ 14 or FMS > 14. The FMS subtests, namely, in-line lunge, trunk stability push-up (TSPU), and quadruped rotary stability, were also performed. In one-year follow-up, the sport injury incidence was also recorded. Significant differences in sprint, agility, and FMS performance were found between the junior basketball and soccer athletes. Individual FMS scores of the in-line lunge, TSPU, and quadruped rotary stability were evaluated. No significant differences in sprint, VJ, and agility scores were found between FMS ≤ 14 and FMS > 14. FMS total score ≤ 14 was significantly associated with high sport injury occurrence. The scores of sprint, agility, and FMS performance were differed between basketball and soccer athletes. The scores of sprint, VJ, and agility tests did not have differences with sport injury risks and occurrences, but the FMS score was associated with sport injury occurrence. 



#2 Nonunion of a Stress Fracture at the Base of the Second Metatarsal in a Soccer Player Treated by Osteosynthesis with the Bridging Plate Fixation Technique 

Reference: Case Rep Orthop. 2020 Dec 22;2020:6649443. doi: 10.1155/2020/6649443. eCollection 2020. 

Authors: Futoshi Morio, Shota Morimoto, Shintaro Onishi, Toshiya Tachibana, Tomoya Iseki

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Summary: A stress fracture of the second metatarsal base in soccer players is extremely rare. In this case study, we report a nonunion of a stress fracture at the base of the second metatarsal in a female soccer player who had persistent pain despite continued conservative treatment, who then was treated with the bridging plate fixation technique. A 19-year-old female college soccer player complained of pain on the dorsum of her right midfoot during a game without history of trauma and was conservatively treated for 6 months. Radiographic examination showed an oblique fracture with small bone fragment at the proximal base of the second metatarsal and computed tomography demonstrated sclerotic change around the fracture site. We diagnosed her with nonunion of a stress fracture at the base of the second metatarsal and performed operative treatments using autogenous cancellous iliac bone grafting and plate fixation bridging a second metatarsal and medial cuneiform with a locking plate. At 4 months after the initial surgery, she was able to return to playing soccer at preinjury level without complications or pain. We report a rare case of nonunion of a stress fracture at the base of the second metatarsal in a female soccer player without underlying diseases. Surgical treatment was applied, because the conservative treatment was ineffective for 6 months and led to nonunion. The plate fixation technique bridging the second metatarsal and medial cuneiform was a useful option to attain the bone fusion for small fracture fragment for a treatment of nonunion of a stress fracture at the base of the second metatarsal. 



#3 A Preliminary Analysis of the Importance of Distance, Angle, and Insight When Soccer Referees Make Penalty Decisions

Reference: Front Sports Act Living. 2021 Jan 8;2:595703. doi: 10.3389/fspor.2020.595703. eCollection 2020. 

Authors: Bjørn Tore Johansen, Martin Kjeøen Erikstad

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Summary: Soccer referees move freely on the pitch to place themselves in the best location for making decisions. While Football Association UK (FA) highlights that a referee should never be more than 20 m away from the playing situation, previous studies have been inconsistent in indicating appropriate distance to a situation for increasing the likelihood of a correct decision. Further, appropriate angle and insight are also likely to influence the correctness of referees' decisions. The aim of this study was to provide an initial investigation of elite referees' positioning in the field (distance, angle, and insight) when making correct and erroneous decisions in potential penalty situations. An expert panel (EP) consisting of two active referees with relevant academic background analyzed referees positioning when making correct or erroneous decisions regarding penalties. The EP were asked to qualitatively analyze referees positioning in selected video clips by using recommended technical refereeing criteria and practical guidelines (i.e., the referee's distance from, angle to, and insight into the penalty situations). Of the 42 situations evaluated, the results revealed that the EP termed the referees positioning as good in terms of angle and insight in 25 and 21 situations, respectively. The angle was average in seven situations and poor in 10 situations, and the insight were average in 10 situations and poor in 11 situations. The match referee was <10 meters away in 12 situations, 10-20 m away in 22 situations, and >20 meters away in eight situations. Results revealed that referees' positioning that resulted in the highest rate of correct decisions were when the distance were under 10 meters (83% correct decisions), good angle (88%), and good insight (86%). In contrast, referees were poorly positioned in terms of angle and/or insight in nine of the 15 erroneous decisions made. Although the present study was a preliminary qualitative investigation containing a limited number of potential penalty situations, the findings indicated that soccer referees are more likely to produce a correct decision in potential penalty situations when the distance to the situation is under 10 meters, when the insight to the situation is good and the angle to the incident is good. In contrast, the match referees generally had a poor starting position to assess the penalty situations where they landed on a wrong decision. While previous studies have been somewhat inconsistent in indicating optimal referee positioning in soccer, the present study highlights the potential value of a more qualitative approach to understand referees' positioning and subsequent decision-making accuracy. 



#4 The Influence of Injury History on Countermovement Jump Performance and Movement Strategy in Professional Soccer Players: Implications for Profiling and Rehabilitation Foci

Reference: J Sport Rehabil. 2021 Jan 25;1-6. doi: 10.1123/jsr.2020-0243. Online ahead of print. 

Authors: Andy Mitchell, Craig Holding, Matt Greig 

Summary: Professional soccer players who have sustained a lower limb injury are up to 3× more likely to suffer a reinjury, often of increased severity. Previous injury has been shown to induce compensatory strategies during neuromuscular screening tests, which might mask deficits and lead to misinterpretation of readiness to play based on task outcome measures. The aim was to investigate the influence of previous injury in professional soccer players on countermovement jump (CMJ) performance and movement strategy. Professional soccer club competing in the English Championship (tier 2). Outfield players with a minimum of 6 years as a professional. Players were categorized as previously injured (n = 10) or not injured (n = 10). All players completed double- and single-leg CMJ trials. CMJ performance was quantified as jump height and flight time:contraction time ratio. CMJ movement strategy was quantified as force-time history, differentiating eccentric and concentric phases and CMJ depth. Double-leg CMJ was not sensitive to previous injury in performance or movement strategy. In contrast, single-leg CMJ performance was impaired in players with previous injury, who generated significantly lower eccentric and concentric peak force and rate of force development, and a deeper countermovement. Impaired single-leg CMJ performance was also evident in the nonaffected limb of previously injured players, suggesting cross-contamination. Hierarchical ordering revealed that the eccentric phase of the CMJ contributed little to performance in previously injured players. In noninjured players, the eccentric rate of force development and concentric peak force were able to account for up to 89% of the variation in CMJ performance. Single-leg CMJ is advocated for player profiling, being more sensitive to previous injury, and negating the opportunity for interlimb compensation strategies. Movement strategy deficits in previously injured players suggest rehabilitation foci specific to eccentric force development. 



#5 Testing protocol affects the velocity at VO 2max in semi-professional soccer players

Reference: Res Sports Med. 2021 Jan 25;1-11. doi: 10.1080/15438627.2021.1878460. Online ahead of print. 

Authors: Andrea Riboli, Giuseppe Coratella, Susanna Rampichini, Eloisa Limonta, Fabio Esposito

Summary: The aim was to compare three different protocols to assess the velocity associated with the maximal oxygen uptake (Vmax) in soccer players. Sixteen semi-professional soccer players performed three maximum incremental tests on treadmill: two continuous protocols [1 km·h-1·min-1 (CP1); and 1 km·h-1 every 2 min (CP2)], and one discontinuous (DP) protocol to determine Vmax, maximum oxygen uptake (VO2max) and oxygen cost of running (i.e., the slope of the VO2 vs velocity relationship at submaximal exercise). Vmax was higher in CP1> CP2> DP (19.4 ± 1.7, 17.4 ± 1.2, 16.1 ± 1.1 km·h-1 for CP1, CP2, and DP, respectively; P < 0.05 ES: 0.09 to 3.36). No difference in VO2max was found between CP1, CP2 and DP (P > 0.05). Oxygen cost of running showed between-protocol differences (CP1> CP2> DP; P < 0.05; ES: 0.28 to 3.30). Vmax was higher when determined using continuous vs discontinuous protocols due to the greater overestimation in oxygen cost of running. Such differences in Vmax should be considered to optimize acute physiological responses during high-intensity running activities. 



#6 How does the mid-season coach change affect physical performance on top soccer players? 

Reference: Physiol Behav. 2021 Jan 21;232:113328. doi: 10.1016/j.physbeh.2021.113328. Online ahead of print. 

Authors: Berni Guerrero-Calderón, Adam Owen, José Alfonso Morcillo, Alfonso Castillo-Rodríguez

Summary: The aim of this study was to analyze the locomotion and metabolic responses of professional players in the top three competitive standards of Spanish soccer (First, Second and Second 'B' division) during the four weeks before and after dismissal the coach. Training and match load data were analyzed separately (n = 1189 events) by coach (dismissed coach and the new coach) and Wilcoxon-test was performed to compare data between coaches. In training, players covered longer distance in all speed ranges >14 km•h - 1 with the coach dismissed; medium (14-18 km•h - 1), high (18-21 km•h - 1), very-high (21-24 km•h - 1) and sprint running distance (>24 km•h - 1) (d = 0.53, 0.46, 0.58 and 0.54; respectively) on first division; and equivalent distance index and accelerations events (d = 0.63 and 0.50; respectively) on second division. Lower differences were found in matches, in which the dismissed coach showed higher equivalent distance index, accelerations and decelerations events (d = 0.69, 0.68 and 0.61; respectively) compared to the new coach in the second division. Therefore, the players covered longer high-intensity distance with the dismissed coach than the new coach in training, whilst a similar performance was found in the competition. These results suggest that the coach turnover at mid-season did no increase the players' physical performance either in training or in competition. 



#7 An 11-week school-based 'health education through football programme' improves health knowledge related to hygiene, nutrition, physical activity and well-being-and it's fun! A scaled-up, cluster-RCT with over 3000 Danish school children aged 10-12 years old 

Reference: Br J Sports Med. 2021 Jan 28;bjsports-2020-103097. doi: 10.1136/bjsports-2020-103097.

Authors: Malte Nejst Larsen, Anne-Marie Elbe, Mads Madsen, Esben Elholm Madsen, Christina Ørntoft, Knud Ryom, Jiri Dvorak, Peter Krustrup

Summary: Our large-scale cluster randomised controlled trial aimed to investigate the effects on health knowledge and enjoyment of an 11 week 'health education through football' programme for children aged 10-12 years old. 3127 Danish school children (49% girls) aged 10-12 years from a total of 154 schools located in 63% of the Danish municipalities (69 of 98) took part in the analysis. A 5:1 cluster randomisation was performed at school level for the intervention group (IG) or the control group (CG). The twice-weekly 45 min intervention was the '11 for Health in Denmark' programme, which includes health education, football drills and small-sided games. The health education element focused on hygiene, nutrition, physical activity and well-being. Outcomes: The participants completed a 34-item multiple-choice computer-based health knowledge questionnaire preintervention and postintervention. IG also evaluated whether the programme was enjoyable. Between-group differences (p<0.05) were observed in overall health knowledge in favour of IG (+7.2% points, 95% CI 6.1% to 8.4%, effect size, ES:0.59), with similar effects for girls (+7.4% points, 95% CI 5.9% to 9.0%, ES:0.57) and for boys (+7.0% points, 95% CI 5.3% to 8.7%, p<0.05, ES:0.51). Marked between-group differences were observed in favour of IG, for health knowledge related to hygiene (IG vs CG:+13.9% points, 95% CI 11.1% to 16.7%, ES:0.53), nutrition (+10.3% points, 95% CI 8.5% to 12.1%, ES:0.53), physical activity (+5.9% points, 95% CI 4.1% to 7.7%, ES:0.36) and well-being (+4.4% points, 95% CI 2.7% to 6.1%, ES:0.28). Both girls and boys gave the programme moderate to high scores for enjoyment (3.6±1.0 and 3.7±1.1, respectively). Health education through sport, using the '11 for Health' model, was enjoyable for girls and boys aged 10-12 years old, and improved health knowledge related to hygiene, nutrition, physical activity and well-being. 



#8 Elite football of 2030 will not be the same as that of 2020: What has evolved and what needs to evolve?

Reference: Scand J Med Sci Sports. 2021 Feb;31(2):493-494. doi: 10.1111/sms.13876. 

Authors: Damian J Harper, Gareth N Sandford, Jo Clubb, Megan Young, Matt Taberner, Dave Rhodes, Chris Carling, John Kiely



#9 The 2015 U.S. Soccer Federation header ban and its effect on emergency room concussion rates in soccer players aged 10-13

Reference: J Can Chiropr Assoc. 2020 Dec;64(3):187-192. 

Authors: Rahim Lalji, Hayden Snider, Noah Chow, Scott Howitt

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Summary: In 2015, the U.S. Soccer Federation banned heading for players aged 10-13. The purpose was to assess the change in proportion of children aged 10-13 playing soccer in the US presenting to an Emergency Department (ED) with a concussion in relation to any other injury before and after the ban. Analysis was restricted to soccer athletes between 10-13 years that reported to a National Electronic Injury Surveillance System (NEISS) participating hospital ED following injury in 2013-2014 and 2016-2017. Multivariable logistic regression was performed to assess the association between year of injury and concussion diagnosis in relation to other injury diagnosis after adjusting for age, sex, and ethnicity. Concussion in relation to other injuries showed a significant increase in 2016-2017 when compared to 2013-2014 after adjustment (OR= 1.286, 95%CI = 1.090-1.517). These results suggest that banning heading may not reduce concussion within this population. However, significant confounders, including increased reporting, were not controlled for. 



#10 Implementing Strength Training Strategies for Injury Prevention in Soccer: Scientific Rationale and Methodological Recommendations 

Reference: Int J Sports Physiol Perform. 2021 Jan 27;1-6. doi: 10.1123/ijspp.2020-0862. Online ahead of print. 

Authors: Marco Beato, Sergio Maroto-Izquierdo, Anthony N Turner, Chris Bishop 

Summary: Due to the negative effects that injuries have on performance, club finances, and long-term player health (permanent disability after a severe injury), prevention strategies are an essential part of both sports medicine and performance. Purpose: To summarize the current evidence regarding strength training for injury prevention in soccer and to inform its evidence-based implementation in research and applied settings. Conclusions: The contemporary literature suggests that strength training, proposed as traditional resistance, eccentric, and flywheel training, may be a valid method to reduce injury risk in soccer players. Training strategies involving multiple components (eg, a combination of strength, balance, plyometrics) that include strength exercises are effective at reducing noncontact injuries in female soccer players. In addition, the body of research currently published supports the use of eccentric training in sports, which offers unique physiological responses compared with other resistance exercise modalities. It seems that the Nordic hamstring exercise, in particular, is a viable option for the reduction of hamstring injuries in soccer players. Moreover, flywheel training has specific training peculiarities and advantages that are related to the combination of both concentric and eccentric contraction, which may play an important role in injury prevention. It is the authors' opinion that strength and conditioning coaches should integrate the strength training methods proposed here in their weekly training routine to reduce the likelihood of injuries in their players; however, further research is needed to verify the advantages and disadvantages of these training methods to injury prevention using specific cohorts of soccer players. 



#11 The Moral Gatekeeper: Soccer and Technology, the Case of Video Assistant Referee (VAR) 

Reference: Front Psychol. 2021 Jan 12;11:613469. doi: 10.3389/fpsyg.2020.613469. eCollection 2020. 

Authors: Ilan Tamir, Michael Bar-Eli

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Summary: Video assistant referee was officially introduced into soccer regulations in 2018, after many years in which referee errors were justified as being "part of the game." The technology's penetration into the soccer field was accompanied by concerns and much criticism that, to a large degree, continues to be voiced with frequency. This paper argues that, despite fierce objections and extensive criticism, VAR represents an important revision in modern professional soccer, and moreover, it completes a moral revolution in the evolution of the sport as a whole. Theoretically speaking, this technology enables an improvement in the sport's professional standards and its public image and prestige, and especially its moral standards - Fair play. Furthermore, the introduction of this technology makes it possible to discover additional weaknesses (Standardization for extra time, a clear definition of a handball offense and more) that professional soccer regulations will probably be forced to address in the future. 



#12 The Goal Scale: A New Instrument to Measure the Perceived Exertion in Soccer (Indoor, Field, and Beach) Players 

Reference: Front Psychol. 2021 Jan 7;11:623480. doi: 10.3389/fpsyg.2020.623480. eCollection 2020. 

Authors: Luis Felipe Tubagi Polito, Marcelo Luis Marquezi, Douglas Popp Marin, Marcelo Villas Boas Junior, Maria Regina Ferreira Brandão

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Summary: The rating of perceived exertion (RPE) can be used to monitor the exercise intensity during laboratory and specific tests, training sessions, and to estimate the internal training load of the athletes. The aim of the present study was to develop and validate a specific pictorial perceived exertion scale for soccer players (indoor, field, and beach soccer) called GOAL Scale. The pictorial GOAL Scale (six drawings; 1 "low exertion" to 6 "exhaustion") was validated for twenty under-17 soccer players (16.4 ± 0.68 years; 175.4 ± 9 cm; 66.4 ± 7.7 kg; % fat mass 12.4 ± 3.3). In the validation phase, the athletes were evaluated in a progressive protocol involving stimuluses of 3 min with 1 min for the rest into the stages until the voluntary exhaustion in Maximal Cardiopulmonary Effort Test (MCET), and in the Yo Yo Intermittent Recovery Test - Level 1 (Yo-Yo). The RPE identified by the GOL Scale, by the Borg Scale 6 - 20 and by the Cavasini Scale, as well as the heart rate (HR), perceptual of the heart rate (%HRmax) and the blood lactate concentration ([La]) were immediately evaluated after each stage of both tests. Spearman's correlation coefficient (p < 0.05) was used. Construct scale validity was examined by regressing GOAL Scale against Borg Scale 6 - 20 and Cavasini Scale and concurrent scale validity was investigated by regressing GOAL Scale against HR, beats/min and blood lactate concentration (mmol/L) during two progressive tests. There was a significant correlation values of the GOAL Scale with Borg Scale (r = 0.93; r = 0.88), Cavasini Scale (r = 0.91; r = 0.90), %HRmax (r = 0.91; r = 0,86), HR (r = 0.87; r = 0.83) and lactate (r = 0.68; r = 0.83) during tests (Maximal Incremental Cardiopulmonary Test and Yo-Yo test, respectively). The results evidenced concurrent and construct validity of the GOAL Scale across a wide range of exercise intensity. The absence of verbal anchors makes the use of this instrument to soccer, futsal and beach soccer athletes of different languages and different literacy levels possible. 






Dose-Response Relationships between Training Load Measures and Physical Fitness in Professional Soccer Players

The aim of this cohort study was two-fold: (i) to analyze within-group changes of final velocity in a 30-15 intermittent fitness test (VIFT), final velocity in a Vameval test (Vvameval), 20-m sprint and countermovement jump (CMJ); (ii) to explore the relationships between VIFT and Vvameval outcomes and their changes with internal and external loads.





Acceleration and High-Speed Running Profiles of Women’s International and Domestic Football Matches

The aim of the present study was to compare the acceleration, deceleration, and high-speed running profiles of players during international and domestic matches and to determine if differences were apparent across playing positions (defenders, midfielders, and attackers).





Latest research in football - week 14 - 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 Does Warm-up Type Matter? A Comparison between Traditional and Functional Inertial Warm-up in Young Soccer Players 

Reference: J Funct Morphol Kinesiol. 2020 Nov 19;5(4):84. doi: 10.3390/jfmk5040084. 

Authors: Giovanni Fiorilli, Federico Quinzi, Andrea Buonsenso, Giulia Di Martino, Marco Centorbi, Arrigo Giombini, Giuseppe Calcagno, Alessandra di Cagno 

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Summary: Functional inertial training, a popular high-intensity training mode, provides high neuromuscular activation, developing proprioception, postural control, power, and sprint time. Aim of the study was to assess the acute effects of two types of warm-up (WU), inertial warm-up (IWU) vs. traditional warm-up (TWU), on explosive and reactive strength, sprint, and Change of Directions (COD) in young soccer players. In a randomized cross-over design study, twelve soccer players (aged 13.3 ± 0.7) performed 16 min of IWU and 16 min of TWU. IWU and TWU were spaced two weeks apart. Pre and post intervention tests, aimed at assessing explosive and reactive strength, sprint, and COD ability included: Squat Jump test (SJ), Countermovement Jump test (CMJ), Drop Jump test (DJ), Seven Repetition Hopping test (7R-HOP), 40 m-sprint test (40 m), and Illinois Agility Test (IAT). RM-ANOVA, used to compare differences between IWU and TWU effects (the level of significance set at ρ ≤ 0.05), showed enhanced performance after the IWU compared to the TWU. In addition, the effects of the IWU on performance lasted longer after the IWU than after the TWU. For IAT, the enhanced effects of IWU on performance lasted up to ten minutes after the administration of the IWU. Our results suggest that IWU affects functional changes displaying earlier adaptation in explosive and reactive strength with longer lasting effects compared to TWU and it could be recommended in young soccer athletes as a WU procedure. 



#2 Bioimpedance Vector References Need to Be Period-Specific for Assessing Body Composition and Cellular Health in Elite Soccer Players: A Brief Report 

Reference: J Funct Morphol Kinesiol. 2020 Oct 1;5(4):73. doi: 10.3390/jfmk5040073. 

Authors: Tindaro Bongiovanni, Gabriele Mascherini, Federico Genovesi, Giulio Pasta, Fedon Marcello Iaia, Athos Trecroci, Marco Ventimiglia, Giampietro Alberti, Francesco Campa

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Summary: Bioimpedance data through bioimpedance vector analysis (BIVA) is used to evaluate cellular function and body fluid content. This study aimed to (i) identify whether BIVA patters differ according to the competitive period and (ii) provide specific references for assessing bioelectric properties at the start of the season in male elite soccer players. The study included 131 male soccer players (age: 25.1 ± 4.7 yr, height: 183.4 ± 6.1 cm, weight: 79.3 ± 6.6) registered in the first Italian soccer division (Serie A). Bioimpedance analysis was performed just before the start of the competitive season and BIVA was applied. In order to verify the need for period-specific references, bioelectrical values measured at the start of the season were compared to the reference values for the male elite soccer player population. The results of the two-sample Hotelling T2 tests showed that in the bivariate interpretation of the raw bioimpedance parameters (resistance (R) and reactance (Xc)) the bioelectric properties significantly (T2 = 15.3, F = 7.6, p ≤ 0.001, Mahalanobis D = 0.45) differ between the two phases of the competition analyzed. In particular, the mean impedance vector is more displaced to the left into the R-Xc graph at the beginning of the season than in the first half of the championship. For an accurate evaluation of body composition and cellular health, the tolerance ellipses displayed by BIVA approach into the R-Xc graph must be period-specific. This study provides new specific tolerance ellipses (R/H: 246 ± 32.1, Xc/H: 34.3 ± 5.1, r: 0.7) for performing BIVA at the beginning of the competitive season in male elite soccer players. 



#3 Body Composition Changes over Multiple Academic Years in Female Collegiate Soccer Players

Reference: J Funct Morphol Kinesiol. 2020 Sep 28;5(4):72. doi: 10.3390/jfmk5040072. 

Authors: Austin Katona, Caroline Riewe, Angela Bruzina, Nicholas J Ollberding, Mary Ankrom, Jon Divine, Robert Mangine, Abigail Peairs

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Summary: Body composition plays a key role in overall health and sports performance and its assessment is an important part of many athletic programs. The purpose of this study was to describe longitudinal changes in body composition for collegiate female soccer players in order to provide data to inform future training and nutrition interventions for this population. A linear mixed-model (LMM) approach was used to analyze four years of pre- and post-season body composition data, including total mass, fat-free mass (FFM), fat mass, and body fat percentage (%BF) for 49 athletes. Athletes gained an average of 0.5 kg FFM during the season (p < 0.05) and increased total mass, FFM, fat mass, and %BF (2.5 kg, 1.1 kg, 1.7 kg, and 1.7%, respectively; p < 0.05) over four years. Freshmen experienced a 1.5 kg gain in total mass pre- to post-season (p < 0.05), while no changes in total mass or body composition were seen in other grade levels. Gains in %BF during the off season between Freshman and Sophomore years represented negative changes in body composition that should be addressed further. These results can help interdisciplinary athlete care teams optimize training programs in this population by understanding what changes are expected over multiple years. Normalizing these changes may also help the promotion of realistic body composition goals and the development of positive training and dietary habits. 



#4 Effects of Hoverboard on Balance in Young Soccer Athletes 

Reference: J Funct Morphol Kinesiol. 2020 Aug 6;5(3):60. doi: 10.3390/jfmk5030060. 

Authors: Stefano Moffa, Angelica Perna, Gabriele Candela, Alessandro Cattolico, Carmine Sellitto, Paolo De Blasiis, Germano Guerra, Domenico Tafuri, Angela Lucariello

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Summary: Hoverboards are always more popular among children. Hoverboards are to them like a game or a mean of transport, but they could be used as a valid and useful instrument in children's training programs to improve their performance. In this study, we compared the athletic performance of two groups of 12 children. A total of 24 children aged between 8 and 11 years followed a similar training program for five months, but the first group used a hoverboard (Hb+ group: Age: Standard Deviation (SD) = 1.15 Mean = 9.66; Weight: SD = 5.90 Mean = 32; Height: SD = 7.64 Mean = 135.08) for some of the training time, differently from the second group (Hb- group: Age: SD = 1.15 Mean = 9.66; Weight: SD = 5.82 Mean = 31.16; Height: SD = 7.66 Mean = 136.16), which never used it. All of the children were asked to complete three tests (one leg test, stork test and balance beam walking test) before starting their own training program and after five months, to evaluate how their performances changed in terms of time. Comparing the recorded time difference between T0 and T1 of the Hb+ group with the same difference measured in Hb- group, it was found that there was a statistically significant difference (p value < 0.05) between these data for all three tests. Children who used the hoverboard in their training program achieved better result than children who did not use it. In the future, the hoverboard could help athletes to improve their performances, possibly applying it not only in football training, but even in other sports. 



#5 Body Fat Assessment in International Elite Soccer Referees 

Reference: J Funct Morphol Kinesiol. 2020 Jun 6;5(2):38. doi: 10.3390/jfmk5020038. 

Authors: Cristian Petri, Francesco Campa, Vitor Hugo Teixeira, Pascal Izzicupo, Giorgio Galanti, Angelo Pizzi, Georgian Badicu, Gabriele Mascherini

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Summary: Soccer referees are a specific group in the sports population that are receiving increasing attention from sports scientists. A lower fat mass percentage (FM%) is a useful parameter to monitor fitness status and aerobic performance, while being able to evaluate it with a simple and quick field-based method can allow a regular assessment. The aim of this study was to provide a specific profile for referees based on morphological and body composition features while comparing the accuracy of different skinfold-based equations in estimating FM% in a cohort of soccer referees. Forty-three elite international soccer referees (age 38.8 ± 3.6 years), who participated in the 2018 Russian World Cup, underwent body composition assessments with skinfold thickness and dual-energy X-ray absorptiometry (DXA). Six equations used to derive FM% from skinfold thickness were compared with DXA measurements. The percentage of body fat estimated using DXA was 18.2 ± 4.1%, whereas skinfold-based FM% assessed from the six formulas ranged between 11.0% ± 1.7% to 15.6% ± 2.4%. Among the six equations considered, the Faulkner's formula showed the highest correlation with FM% estimated by DXA (r = 0.77; R2 = 0.59 p < 0.001). Additionally, a new skinfold-based equation was developed: FM% = 8.386 + (0.478 × iliac crest skinfold) + (0.395 × abdominal skinfold, r = 0.78; R2 = 0.61; standard error of the estimate (SEE) = 2.62 %; p < 0.001). Due to these findings, national and international federations will now be able to perform regular body composition assessments using skinfold measurements. 



#6 Injury prevention effects of stretching exercise intervention by physical therapists in male high school soccer players

Reference: Scand J Med Sci Sports. 2020 Nov;30(11):2178-2192. doi: 10.1111/sms.13777. Epub 2020 Aug 2. 

Authors: Nobuhide Azuma, Fujiko Someya

Summary: We aimed to examine the prevalence of injury after physical therapy intervention for muscle tightness and injury prevention in male high school soccer players. A randomized controlled trial was conducted. Participants comprised 124 players from two high schools who competed in national tournament soccer games held from April 2018 to March 2019. Players were randomly divided into intervention (with a 12-week stretching intervention by physical therapists) and control groups (without the intervention). Players and coaches provided written information regarding injuries and daily training and match times; physical therapists visited each team weekly to collect data and review documentation. Muscle tightness and injury incidence, number, type, location, circumstances, situations, severity, and contents during the 12-week intervention period and a subsequent 40-week observation period were compared between groups. Injuries were significantly lower with intervention during the 40-week observation period (P < .01) but not during the 12-week intervention period (P = .44). Injury types mainly included disorder, non-contact, lower-limb/trunk, and muscle/tendon injuries. Significant interactions were observed for all tightness-test measurement items. The intervention group showed significant improvements in heel-buttock distance, and straight leg-raise and hip rotation angles (pre-intervention < 12 weeks < 52 weeks), as well as significant improvements in ankle dorsiflexion angles at 12 and 52 weeks (relative to pre-intervention values). Instructed stretching exercises, personally designed by physical therapists to address muscle tightness, improved the range of motion and trunk flexibility, with a positive effect on the injury rate in male high school soccer players, especially for non-contact disorder injuries during training. 



#7 Associations of Body Composition, Maximum Strength, Power Characteristics with Sprinting, Jumping, and Intermittent Endurance Performance in Male Intercollegiate Soccer Players

Reference: J Funct Morphol Kinesiol. 2021 Jan 7;6(1):E7. doi: 10.3390/jfmk6010007. 

Authors: Ai Ishida, S Kyle Travis, Michael H Stone

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Summary: The purpose of this study was to determine the relationships between body composition, strength, power characteristics, sprinting, jumping, and intermittent endurance performance in collegiate male players. Twenty-three players participated (19.7 ± 1.6 yrs; 71.8 ± 7.1 kg; 176.5 ± 5.1 cm). Measurements of interest in body composition included body fat percentage (BF%), lean body mass (LBM), and body mass (BM). Power characteristics were measured with an unloaded squat jump (SJ0) and loaded SJ at 20 kg (SJ20) and 40 kg (SJ40), and unloaded countermovement jump (CMJ0). Power assessments included peak power (PP) and PP allometrically scaled (PPa). Strength characteristics were assessed using isometric mid-thigh pull. Strength assessment included isometric peak force (IPF) and IPF allometrically scaled (IPFa). Performance measures included 10m and 20 m sprint time, CMJ0 jump-height, and Yo-Yo intermittent endurance test level 1 distance. Significant correlations ranging from moderate to very large were found for LBM and CMJ jump height (CM0 JH) (p = 0.01, r = 0.50); BF% and sprint times at 10 m (p = 0.03, r = 0.44) and 20 m (p = 0.02, r = 0.50). PP and PPa from SJ0 and CMJ0 were significantly correlated to 10m sprint time (p < 0.05, r = -0.45 to -0.53) and 20 m sprint time (p < 0.05, r = -0.40 to -0.49). Our findings agree with previous literature in that body composition and power characteristics are directly related to soccer-related performance. 



#8 Cell integrity indicators in university athletes: comparison among playing positions in indoor football 

Reference: J Sports Med Phys Fitness. 2021 Jan 22. doi: 10.23736/S0022-4707.21.12008-0. Online ahead of print. 

Authors: Priscila C Martins, Paula DA Silva, Diego A Silva

Summary: The aim of this study was to compare cell integrity indicators according to the playing position in university indoor football athletes. The sample consisted of 34 university athletes (20 female and 14 male). Dependent variables were cell integrity indicators: total body water (TBW), intracellular water (ICW), extracellular water (ECW), ECW/ICW ratio, body cell mass (BCM), ECW/BCM ratio, phase angle (PhA), resistance (R), Xc (reactance) and impedance (Z), evaluated by the electrical bioimpedance method. Independent variable was the playing position: goalkeeper (a), defender (a), winger (left and right) and pivot collected through questionnaire. Control variables were age, time of sport practice, participation in competitions per year and training load obtained by applying the anamnesis form, and body fat and fat and bone-free mass were obtained through dual emission X-ray absorptiometry (DXA). Covariance analysis (ANCOVA) was used, with post-roc Tukey's test, to identify difference between groups, with p <0.05. In the adjusted analysis, female athletes in the defense position had BCM values (31.1 ±2.1) higher than those in the wing position (25.8 ±1.1) (p <0.01). In males, pivots showed higher ICW values (31.47 ±0.77) when compared to defenders (25.7 ±0.8) (p = 0.02). In addition, goalkeepers had higher TBW values (52.7 ±2.5) compared to wingers (42.3 ±1.2) (p = 0.03). Cell integrity indicators may vary according to the playing position in indoor football. 



#9 Reopening elite sport during the COVID-19 pandemic: Experiences from a controlled return to elite football in Denmark

Reference: Scand J Med Sci Sports. 2021 Jan 21. doi: 10.1111/sms.13915. Online ahead of print. 

Authors: Lars Pedersen, Jens Lindberg, Rune Rasmussen Lind, Hanne Rasmusen

Summary: As the SARS-CoV-2 infection rate decreased in spring 2020, phased reopening of Danish society began, including a reopening of elite football (soccer), adhering to a strict protocol. In this study, we report the consequences of resumption of competitive play in the two best football (soccer) leagues for men in Denmark measured by number of SARS-CoV-2 positive players. The players were tested weekly for SARS-CoV-2 for 11 consecutive weeks. The test protocol comprised 26 teams with 748 players. In total, 6511 tests were done with a positivity rate of 0.06%. The incidence rate of players testing positive for SARS-CoV-2 was 0.53% (4/748). There were no signs of a chain of infection. We found a low incidence rate of SARS-CoV-2, and based on this, a controlled reopening of professional football strictly following a detailed protocol appears safe for the players. 



#10 The Influence of Child-Related Factors on Caregiver Perceptions of Their Child's Sustained Participation in a Community Football Program: A Study of Children with and without Neurodevelopmental Disorders 

Reference: Int J Environ Res Public Health. 2021 Jan 19;18(2):831. doi: 10.3390/ijerph18020831. 

Authors: Carmel Sivaratnam, Bethany Devenish, Tayla Chellew, Nicole Papadopoulos, Jane McGillivray, Nicole Rinehart

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Summary: This study evaluated the influence of activity preference and involvement on season completion in a community-based football program for children with and without neurodevelopmental disorders. Caregivers (n = 1428) of 1529 children aged 4 to 17 (M = 7.27, SD = 1.85), with (n = 175) and without (n = 1354) neurodevelopmental disorders who were currently participating or had previously participated in a group-based NAB AFL Auskick football program completed an online survey. The survey collected information on their child's completion of any attempted seasons of the football program, level of involvement during the sessions and preference for football over other sports and activities. Eighty percent of children with a neurodevelopmental diagnosis had completed all seasons of Auskick, compared with 93% of children without a neurodevelopmental diagnosis. Results indicated that children with neurodevelopmental disorders (n = 135) were 3.71 times less likely to complete a football season than their typically developing peers (n = 903). Higher levels of involvement during football sessions and greater preference for football were linked to a higher football season completion rate, irrespective of neurodevelopmental disability diagnosis. This study highlights the influence of child-related factors, in particular, preference and involvement, on children's sustained participation in community football programs, regardless of neurodevelopmental disability status. 



#11 The effects of residential environment on the condition and fitness of soccer players in the summer 

Reference: J Exerc Rehabil. 2020 Dec 28;16(6):522-528. doi: 10.12965/jer.2040748.374. eCollection 2020 Dec. 

Authors: Jae-Hoon Jang, Chang-Hwa Joo

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Summary: Exercise performance is reduced in hot environments due to physiological responses caused by increased body temperature. A proper residential environment is important for improving the performance and maintaining physical condition of soccer players in the summer. The purpose of this study was to determine the effect of indoor temperature of the resting space during the summer on the fitness and condition of soccer players. A total of 12 K-3 League semiprofessional players without serious injuries in the last 3 months voluntarily participated in the study. Participants performed speed (10 m, 20 m, and 30 m), soccer-specific coordination skill (dribbling), agility, repeated sprints, Yo-Yo intermittent level 2, vertical jump, and questionnaire (fatigue, sleep quality, muscle soreness, stress, and mood) after staying indoor temperature at 20°C, 26°C, and 30°C for one night, respectively. There was no difference among groups in physical fitness (speed, agility, jump, coordination, Yo-Yo intermittent level 2, and repeated sprints). The differences in fatigue and sleep quality were not statistically significant among groups, but they tended to be different. Muscle soreness was similar among all groups. Significant differences were observed between the 20°C and 30°C groups in stress and mood levels. The present study concluded that, while the physical fitness did not differ among groups, the 30°C residential environment was shown to have a negative psychological effect. Considering that many diseases associated with hot weather occur in low residential temperatures, a room temperature of 26°C is recommended for elite soccer players in hot summer weather. 



#12 Effects of home confinement due to COVID-19 pandemic on eccentric hamstring muscle strength in football players 

Reference: Scand J Med Sci Sports. 2020 Oct;30(10):2010-2012. doi: 10.1111/sms.13768. 

Authors: Victor Moreno-Pérez, Juan Del Coso, Daniel Romero-Rodríguez, Luis Marcé-Hernández, Marcelo Peñaranda, Marc Madruga-Parera

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Influence of Players’ Maximum Running Speed on the Team’s Ranking Position at the End of the Spanish LaLiga

The aim was to determine the influence of a player’s peak/maximum running speed on the team’s final ranking position. A second aim was to investigate differences in maximum running speed among playing positions.





A Preseason Training Program With the Nordic Hamstring Exercise Increases Eccentric Knee Flexor Strength and Fascicle Length

The aim of this study was to investigate the collective and individual responses of professional female soccer players engaged in a preseason training program with the NHE regarding eccentric knee flexor strength and biceps femoris long head fascicle length.





Latest research in football - week 13 - 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 Predictive equations for resting metabolic rate are not appropriate to use in Brazilian male adolescent football athletes 

Reference: PLoS One. 2021 Jan 14;16(1):e0244970. doi: 10.1371/journal.pone.0244970. eCollection 2021. 

Authors: Taillan M Oliveira, Paula A Penna-Franca, Christian H Dias-Silva, Victor Z Bittencourt, Fabio F L C Cahuê, Sidnei J Fonseca-Junior, Anna Paola T R Pierucci

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Summary: High accuracy in estimating energy expenditure is essential for enhancing sports performance. The resting metabolic rate (RMR), as a primary component of total energy expenditure (TEE), is commonly estimated using predictive equations. However, these references may not be applicable to adolescent athletes. The purpose of this cross-sectional study was to analyse the differences between predicted RMR in relation to energy expenditure measured by indirect calorimetry (IC) among 45 Brazilian male adolescent football athletes. Indirect calorimetry (IC) and anthropometric (bioimpedance) measurements were recorded at a single visit to the laboratory after fasting overnight. The mean age was 15.6 ± 1.14 years, body mass was 63.05 ± 7.8 kg, and height was 172 ± 7.5 cm. The RMR values predicted by equations proposed by the Food and Agriculture Organization (FAO) (United Nations), Henry and Rees (HR), Harris Benedict (HB), and Cunningham (CUN) were compared with IC RMR values, by correlation analysis. The FAO and HR predictive equations yielded different values from IC (IC: 1716.26 ± 202.58, HR: 1864.87 ± 147.78, FAO: 1854.28 ± 130.19, p = 0.001). A moderate correlation of 0.504 was found between the results of HB and IC. In the survival-agreement model, the CUN equation showed low disagreement with the IC RMR, with error values between 200 and 300 kcal/day. The results showed that HB and CUN yielded similar values as IC, with the CUN equation showing low disagreement with IC; hence, adolescent athletes should undergo evaluation with precise laboratory methods to ensure that accurate information about RMR is recorded. 



#2 Who Will Score? A Machine Learning Approach to Supporting Football Team Building and Transfers

Reference: Entropy (Basel). 2021 Jan 10;23(1):E90. doi: 10.3390/e23010090. 

Authors: Bartosz Ćwiklinski, Agata Giełczyk, Michał Choraś

Summary: The machine learning (ML) techniques have been implemented in numerous applications, including health-care, security, entertainment, and sports. In this article, we present how the ML can be used for building a professional football team and planning player transfers. In this research, we defined numerous parameters for player assessment, and three definitions of a successful transfer. We used the Random Forest, Naive Bayes, and AdaBoost algorithms in order to predict the player transfer success. We used realistic, publicly available data in order to train and test the classifiers. In the article, we present numerous experiments; they differ in the weights of parameters, the successful transfer definitions, and other factors. We report promising results (accuracy = 0.82, precision = 0.84, recall = 0.82, and F1-score = 0.83). The presented research proves that machine learning can be helpful in professional football team building. The proposed algorithm will be developed in the future and it may be implemented as a professional tool for football talent scouts. 



#3 Injury Profile in Women's Football: A Systematic Review and Meta-Analysis 

Reference: Sports Med. 2021 Jan 12. doi: 10.1007/s40279-020-01401-w. Online ahead of print. 

Authors: Alejandro López-Valenciano, Javier Raya-González, Jose Alberto Garcia-Gómez, Alba Aparicio-Sarmiento, Pilar Sainz de Baranda, Mark De Ste Croix, Francisco Ayala

Summary: Football is the most popular sport among women; however, little is known about the injury profile in this population. This information would help design tailored injury risk mitigation strategies that may make football safer for women. The aim of this study was to perform a systematic review and meta-analysis of epidemiological data of injuries in women´s football. A systematic review following PRISMA guidelines was performed up to January 2020 in PubMed, Web of Science, Sportdiscus and the Cochrane Library databases. Twenty-two studies reporting the incidence of injuries in women football were analysed. Two reviewers independently extracted data (intraclass correlation coefficient [ICC] for inter-reviewer reliability = 0.87) and assessed study quality using the STROBE statement, GRADE approach, Newcastle Ottawa Scale and Downs and Black assessment tools. Studies were combined in pooled analyses (injury incidence and injury proportion) using a Poisson random effects regression model. The overall incidence of injuries in female football players was 6.1 injuries/1000 h of exposure. Match injury incidence (19.2 injuries/1000 h of exposure) was almost six times higher than training injury incidence rate (3.5 injuries/1000 h of exposure). Lower extremity injuries had the highest incidence rates (4.8 injuries/1000 h of exposure). The most common types of injuries were muscle/tendon (1.8 injuries/1000 h of exposure) and joint (non-bone) and ligament (1.5 injuries/1000 h of exposure), which were frequently associated with traumatic incidents. Slight/minimal injuries (1-3 days of time loss) were the most common. The incidence rate of injuries during matches in the top five world ranking leagues was higher than the rest of the leagues (19.3 vs 10.7 injuries/1000 h of exposure, respectively). The weighted injury proportion was 1.1 (95% confidence interval = 0.6-1.7) whereby on average players sustained more than one injury per season. Female football players are exposed to a substantial risk of sustaining injuries, especially during matches that require the highest level of performance. To markedly reduce overall injury burden, efforts should focus on introducing and evaluating preventative measures that target match specific dynamics to make football players more capable of responding to the challenges that they have to deal with during match play. 



#4 Influence of Traditional Sporting Games on the Development of Creative Skills in Team Sports. The Case of Football

Reference: Front Psychol. 2020 Dec 23;11:611803. doi: 10.3389/fpsyg.2020.611803. eCollection 2020. 

Authors: Alexandre Oboeuf , Sylvain Hanneton, Joséphine Buffet, Corinne Fantoni, Lazhar Labiadh

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Summary: The aim of this present study is to investigate the influence of three learning contexts on the development of motor creativity of young footballers (8-9 years old). In team sport, creativity is a fundamental issue because it allows players to adapt in an environment of high social uncertainty. To carry out this work, we suggest a method for assessing motor creativity into ecological situations based on the analysis of praxical communications. Creativity originates from an interaction between divergence and convergence. In our case, the number of communications (fluidity) and the diversity of updated communications (flexibility) are our divergence indicators. Convergence, understood as the ability to make good decisions, is assessed by two expert judges (R > 0.90). Sixty boys' football players (M = 8.67; SD = 0.3) coming from three football clubs participated in this research. The study lasted 2 years. Each year, a team of 10 players from each club participated in the research twice a week for 32 weeks (8 months), these groups attended different training sessions: (a) the control group (n = 20) followed a classical learning; (b) the decoding group (n = 20) attended training focused on learning the praxemes of football; (c) the traditional sporting games group (n = 20) followed a training session that was jointly focused on praxemes and the practice of traditional sporting games. The motor creativity of players and groups was assessed both at the beginning and at the end of the year during football matches. Compared to the control group, in the post-test, the group with the highest fluidity is the decoding group (p < 0.001) and the one with the highest fluidity is the traditional sporting games group. The latter group is also the one with the best convergence (p < 0.001). The results showed that traditional games can help develop players' creative abilities. This research invites us to investigate the complementarity between the different offered training. 



#5 Effect of acute football activity and physical fitness on glycaemic and insulinaemic responses in adolescents

Reference: J Sports Sci. 2021 Jan 11;1-9. doi: 10.1080/02640414.2020.1860362. Online ahead of print. 

Authors: Ryan A Williams, Simon Cooper, Karah J Dring, Lorna Hatch, John G Morris, Caroline Sunderland, Mary E Nevill

Summary: The present study examined the metabolic responses to an acute bout of football and the overall and moderating role of physical fitness on these responses, in adolescents. Thirty-six adolescents (16 girls, 20 boys; 12.6±0.5 y) completed two trials (60-min football and 60-min seated rest) separated by 7-d. Capillary blood samples were taken at baseline (60-min prior to exercise/rest), immediately, 30- and 60-min post-exercise and 30-, 60- and 120-min following a standardised lunch (1.5-, 2- and 3-h post-exercise), for the determination of blood glucose and plasma insulin concentrations. The median split of distance covered on the multi-stage fitness test was used to define high- and low-fit groups. Overall plasma insulin tAUC following lunch was lower in high-fit participants compared to low-fit (high-fit: 3784.2±1653.1 pmol·L-1x120min, low-fit: 6457.3±3290.7 pmol·L-1x120min; p<0.001), although there was no acute effect of the football session (p>0.05). Football reduced blood glucose concentration 1-h post-exercise compared to control (exercise: 3.8±0.6 mmol·L-1, rest: 4.6±0.8 mmol·L-1; p<0.001), but this was similar for the high- and low-fit participants (p>0.05). Blood glucose tAUC was not affected by exercise or physical fitness (p>0.05). These data emphasise the importance of physical fitness for metabolic health in adolescents, as well as the utility of football as a popular form of games-based activity for improving glucose regulation. 



#6 Effects of football fitness training on lymphedema and upper-extremity function in women after treatment for breast cancer: a randomized trial 

Reference: Acta Oncol. 2021 Jan 11;1-9. doi: 10.1080/0284186X.2020.1868570. Online ahead of print. 

Authors: Kira Bloomquist, Peter Krustrup, Bjørn Fristrup, Victor Sørensen, Jørn Wulff Helge, Eva Wulff Helge, Eva Soelberg Vadstrup, Mikael Rørth, Sandra C Hayes, Jacob Uth

Summary: Breast cancer survivors are encouraged to be physically active. A recent review suggests that football training is an effective exercise modality for women across the lifespan, positively influencing health variables such as strength, fitness and social well-being. However, football is a contact sport, potentially posing an increased risk of trauma-related injury. Against this backdrop, breast cancer survivors are advised to avoid trauma or injury to the affected or at-risk arm in order to protect against lymphedema onset or exacerbation. The aim of this study was therefore to evaluate the feasibility and safety of Football Fitness training in relation to lymphedema and upper-extremity function after treatment for breast cancer. Sixty-eight women aged 18-75 years, who had received surgery for stage I-III breast cancer and completed (neo) adjuvant chemotherapy and/or radiotherapy within five years, were randomized (2:1) to a Football Fitness group (FFG, n = 46) or a control group (CON, n = 22) for twelve months. Secondary analyses using linear mixed models were performed to assess changes in upper-body morbidity, specifically arm lymphedema (inter-arm volume % difference, dual energy X-ray absorptiometry; extracellular fluid (L-Dex), bioimpedance spectroscopy), self-reported breast and arm symptoms (EORTC breast cancer-specific questionnaire (BR23) and upper-extremity function (DASH questionnaire) at baseline, six- and twelve-month follow-up. We observed similar point prevalent cases of lymphedema between groups at all time points, irrespective of measurement method. At the six-month post-baseline assessment, reductions in L-Dex (extracellular fluid) were found in FFG versus CON. These significant findings were not maintained at the twelve-month assessment. No difference between groups was observed for inter-limb volume difference %, nor any of the remaining outcomes. While superiority of Football Fitness was not observed, the results support that participation in Football Fitness training is feasible and suggests no negative effects on breast cancer-specific upper-body morbidity, including lymphedema. 



#7 Playing Non-Professional Football in COVID-19 Time: A Narrative Review of Recommendations, Considerations, and Best Practices 

Reference: Int J Environ Res Public Health. 2021 Jan 12;18(2):E568. doi: 10.3390/ijerph18020568. 

Authors: Markel Rico-González, José Pino-Ortega, Luca Paolo Ardigò

Summary: The coronavirus disease (COVID-19) pandemic in 2020 resulted in widespread interruption of team sports training and competitions. Our aim was to review the recommendations and best practices in return to play in non-professional football after activity lockdown. The authors searched two electronic databases (PubMed, Web of Science) to extract studies published before September 15 2020. Twenty studies explained recommendations, considerations, or best practices in return to play in football, and all of them were clustered into three groups: (1) training load management (n = 10), (2) medical recommendations (n = 9), and (3) recovery related issues (n = 5). The way to establish a progression in training process should be based on training load management and managing the number of stimuli per time. Following the studies, this training process should be divided into three phases: phase 1-physical distancing should be maintained; phases 2 and 3-group training should start. Medical considerations were clustered into different groups: general, pre- and post- training, during training, education, planning to return to competition, and suggestions for post confinement weeks. In particular, social issues, strict hygiene questions, and continuous PCR testing should be considered in return to play over football season. Finally, since a correlation has been found between high-intensive training loads and immunoglobulin A, nutritional and lifestyle recovery strategies should be performed. Moreover, since immunosuppression has been related to congested schedules (<72 h between matches), football federations should avoid this situation. 



#8 Nontraumatic Exertional Fatalities in Football Players, Part 1: Letter to the Editor

Reference: Orthop J Sports Med. 2020 Dec 29;8(12):2325967120980395. doi: 10.1177/2325967120980395. eCollection 2020 Dec. 

Authors: William M Adams, Samantha E Scarneo-Miller, Rebecca L Stearns, Douglas J Casa

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#9 Internal and External Training Load in Under-19 versus Professional Soccer Players during the In-Season Period 

Reference: Int J Environ Res Public Health. 2021 Jan 11;18(2):E558. doi: 10.3390/ijerph18020558. 

Authors: Sullivan Coppalle, Guillaume Ravé, Jason Moran, Iyed Salhi, Abderraouf Ben Abderrahman, Sghaeir Zouita, Urs Granacher, Hassane Zouhal 

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Summary: This study aimed to compare the training load of a professional under-19 soccer team (U-19) to that of an elite adult team (EAT), from the same club, during the in-season period. Thirty-nine healthy soccer players were involved (EAT [n = 20]; U-19 [n = 19]) in the study which spanned four weeks. Training load (TL) was monitored as external TL, using a global positioning system (GPS), and internal TL, using a rating of perceived exertion (RPE). TL data were recorded after each training session. During soccer matches, players' RPEs were recorded. The internal TL was quantified daily by means of the session rating of perceived exertion (session-RPE) using Borg's 0-10 scale. For GPS data, the selected running speed intensities (over 0.5 s time intervals) were 12-15.9 km/h; 16-19.9 km/h; 20-24.9 km/h; >25 km/h (sprint). Distances covered between 16 and 19.9 km/h, > 20 km/h and >25 km/h were significantly higher in U-19 compared to EAT over the course of the study (p = 0.023, d = 0.243, small; p = 0.016, d = 0.298, small; and p = 0.001, d = 0.564, small, respectively). EAT players performed significantly fewer sprints per week compared to U-19 players (p = 0.002, d = 0.526, small). RPE was significantly higher in U-19 compared to EAT (p = 0.001, d = 0.188, trivial). The external and internal measures of TL were significantly higher in the U-19 group compared to the EAT soccer players. In conclusion, the results obtained show that the training load is greater in U19 compared to EAT. 



#10 Evaluation of the accuracy of different body composition prediction formulas, compared to Dual Energy X-ray Absorptiometry, in soccer players of Colombian professional teams

Reference: Nutr Hosp. 2021 Jan 15. doi: 10.20960/nh.03206. Online ahead of print. [Article in Spanish] 

Authors: Maximiliano Kammerer López, Natalia Del Carmen Ceballos Feria, Maria Camila Mayor Rengifo, Hugo Hernando Hoyos García, Santiago Gómez Velásquez

Summary: Professional soccer both in the local setting and in other countries is highly competitive, and those who practice it must have specific morphological, anthropometric, and body composition characteristics, in addition to constant monitoring of nutritional and training interventions. Currently, the gold-standard criterion for the evaluation of body composition is Dual Energy X-ray Absorciometry (DXA), which is a costly laboratory method with limited use for many professionals. Knowing which field methods obtain similar results to this would allow a better interdisciplinary approach, which could have a positive impact on sports performance. The objective of this study was to evaluate the accuracy of different formulas for predicting fat percentage and fat mass, as compared to DXA, in Colombian soccer team players. A cross-sectional, analytical study using convenience sampling. A total of 79 professional male soccer players, belonging to 4 Colombian first and second division clubs, were included. Thirty anthropometric variables were measured, wherewith a descriptive analysis was performed using the SPSS v.21 program, and a procedure with analytical scope was carried out to establish concordance indices between different measurements using the Bland and Altman method. This statistical process was performed using the library (BlandAltmanLeh) of the statistical program "R". Average age was 23 ± 4.4 years, and the percentage of body fat was estimated using six equations: Jackson and Pollock (7.20 ± 2.58 %), Yuhasz as modified by Carter (7.52 ± 8.50 %), Reilly (10.04 ± 1.43 %), Faulkner (11.23 ± 11.90 %), Pariskova and Buskova (11.08 ± 16.06 %), and Durnin and Womersley (12.41 ± 20,10 %), in addition to the calculation of fat percentage for fat mass using the five-component method (13.17 ± 2.86 %). The percentage of body fat that showed the lowest intermethod difference was fractionation by five components (0.54 ± 3.56), followed by Durnin and Womersley (0.66 ± 3.52). The calculations of fat percentage using the fractionation of 5 components method and the Durnin and Womersley equation were closest to the results obtained by the gold-standard method (DXA) in soccer players of Colombian professional teams. 



#11 Prevalence of Low Energy Availability in Collegiate Women Soccer Athletes 

Reference:  J Funct Morphol Kinesiol. 2020 Dec 18;5(4):96. doi: 10.3390/jfmk5040096. 

Authors: Meghan K Magee, Brittanie L Lockard, Hannah A Zabriskie, Alexis Q Schaefer, Joel A Luedke, Jacob L Erickson, Margaret T Jones, Andrew R Jagim

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Summary: Limited information exists on the prevalence of low energy availability (LEA) in collegiate team sports. The purpose of this study was to examine the prevalence of LEA in collegiate women soccer players. Collegiate women soccer athletes (n = 18, height: 1.67 ± 0.05 m; body mass: 65.3 ± 7.9 kg; body fat %: 24.9 ± 5.6%) had their body composition and sport nutrition knowledge assessed in the pre-season. Energy availability was assessed mid-season using a 4-day dietary log and activity energy expenditure values from a team-based monitoring system. A validated screening tool was used to screen for LEA. The screening tool classified 56.3% of athletes as at risk of LEA (<30 kcal/kg of FFM); however, the actual dietary intake identified 67% as LEA. Athletes identified as non-LEA consumed significantly more absolute (p = 0.040) and relative (p = 0.004) energy than LEA athletes. There was a high prevalence of LEA among collegiate women soccer athletes. Although previously validated in women endurance athletes, the LEA screening tool was not effective in identifying those at risk of LEA in this sample of athletes. 



#12 Detection Accuracy of Soccer Players in Aerial Images Captured from Several Viewpoints

Reference: J Funct Morphol Kinesiol. 2019 Jan 21;4(1):9. doi: 10.3390/jfmk4010009. 

Authors: Takuro Oki, Ryusuke Miyamoto, Hiroyuki Yomo, Shinsuke Hara

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Summary: In the fields of professional and amateur sports, players' health, physical and physiological conditions during exercise should be properly monitored and managed. The authors of this paper previously proposed a real-time vital-sign monitoring system for players using a wireless multi-hop sensor network that transmits their vital data. However, existing routing schemes based on the received signal strength indicator or global positioning system do not work well, because of the high speeds and the density of sensor nodes attached to players. To solve this problem, we proposed a novel scheme, image-assisted routing (IAR), which estimates the locations of sensor nodes using images captured from cameras mounted on unmanned aerial vehicles. However, it is not clear where the best viewpoints are for aerial player detection. In this study, the authors investigated detection accuracy from several viewpoints using an aerial-image dataset generated with computer graphics. Experimental results show that the detection accuracy was best when the viewpoints were slightly distant from just above the center of the field. In the best case, the detection accuracy was very good: 0.005524 miss rate at 0.01 false positive-per-image. These results are informative for player detection using aerial images and can facilitate to realize IAR. 



#13 The Physical Demands of NCAA Division I Women's College Soccer 

Reference: J Funct Morphol Kinesiol. 2019 Dec 12;4(4):73. doi: 10.3390/jfmk4040073. 

Authors: Robert W Sausaman, Matt L Sams, Satoshi Mizuguchi, Brad H DeWeese, Michael H Stone

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Summary: Extensive research into women's collegiate soccer is scarce, leaving gaps in the literature with little information available detailing the physical demands at different standards of play. Our purpose was to elucidate the physical demands of the Division I collegiate level and identify differences between playing positions. Twenty-three field players were observed during four competitive seasons using 10-Hz GPS units (Catapult Sports, Melbourne, Australia). Descriptive statistics and 95% confidence intervals were used to determine group and position-specific physical demands. Linear mixed modelling (LMM) was used to compare attacker, midfielder, and defender position groups. Total distance, high-speed distance, and sprint distance were 9486 ± 300 m, 1014 ± 118 m, and 428 ± 70 m, respectively. Furthermore, attackers were observed to cover the greatest distance at all speeds compared to midfielders and defenders. Our findings suggest that the physical demands of Division I women's soccer differ by position and appear lower compared to higher standards of play. Therefore, coaches and sports scientists responsible for the physical training of Division I collegiate players should consider the specific physical demands of the collegiate level and playing position when prescribing training, as well as in the development of their annual training programs. 



#14 Lateral Ankle Sprains and Their Association with Physical Function in Young Soccer Players 

Reference: Open Access J Sports Med. 2021 Jan 12;12:1-10. doi: 10.2147/OAJSM.S283421. eCollection 2021. 

Authors: Kenichiro Murata, Tsukasa Kumai, Norikazu Hirose

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Summary: Lateral ankle sprain (LAS) in childhood can result in lateral malleolus avulsion fractures; additionally, bone nonunion may occur. Physical maturity relates to the development of bone morphology and physical functionality. It is unknown how changes in physical functionality attributable to physical maturity affect young soccer players with abnormal lateral malleolus (ALM) morphology. Hence, the present study aimed to investigate the bone morphology of the lateral malleolus in young soccer players and to examine its relationship with physical functionality at different maturity levels. Two hundred and ninety young soccer players aged 6-15 years were included. The presence of ALM was assessed using ultrasonography. The subjects were allocated to three groups based on physical maturity (Pre-, Mid-, and Post-peak height velocity age [PHVA]). The prevalence of ALM and the relationship between ALM and physical maturity were examined for body composition, foot pressure distribution, foot alignment, ankle mobility, and single-leg balance. The prevalence of ALM was 17.6%. For physical maturity, the post-PHVA group showed a decrease in ankle dorsiflexion and eversion and an increase in one-leg hop distance compared to the Pre-PHVA group (P < 0.05). In the ALM group, the center of pressure during heel raising was distributed laterally in the Post-PHVA (P < 0.01), and the weight-bearing dorsiflexion angle was decreased in the Mid- and Post-PHVA (P < 0.05). In the Post-PHVA young soccer players, decreased ankle dorsiflexion and eversion and increased one-leg hop distance were observed. The ALM group exhibited lateral loading during heel raising in the Post-PHVA group and decreased weight-bearing ankle dorsiflexion angle in the Mid- and Post-PHVA groups. The findings indicate the importance of secondary prevention of LAS and ultrasonography. Prospective studies of LAS in young athletes are required in the future. 






Quantification of Training Load Relative to Match Load of Youth National Team

The aims of this study were to (1) quantify the external training load relative to match load in days before a subsequent international game and (2) examine the cumulative training load in relation to match load of U-17 national team soccer players.





A Meta-Analytical Comparison of the Effects of Small-Sided Games vs. Running-Based High-Intensity Interval Training on Soccer Players’ Repeated-Sprint Ability

This systematic review with a meta-analysis was conducted to compare the effects of small-sided games (SSGs)-based interventions with the effects of running-based high-intensity interval training (HIIT) interventions on soccer players’ repeated sprint ability (RSA).





Latest research in football - week 12 - 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 Physical performance development in a female national team soccer program 

Reference: J Sci Med Sport . 2020 Dec 31;S1440-2440(20)30864-1. doi: 10.1016/j.jsams.2020.12.009.

Authors: Robert A Poehling, Ming-Chang Tsai, Sarah A Manson, Michael S Koehle, Cesar M P Meylan

Summary: Significant resources are invested in maximizing player performance without extensive knowledge of the athletic progression of elite female soccer players during their career. The aim of the current study was therefore to investigate the change in physical performance characteristics in 12- to 34-year-old female soccer players in a national team program. Physical performance was assessed across five years and 657 testing occasions (n = 143) using anthropometrics, 40 m sprint (10 m split), broad jump, countermovement jump, squat jump, and 30-15 intermittent fitness test (IFT). Using a Gaussian mixture model, Youth and Senior groups were bifurcated at approximately 23 years old. Subsequent linear mixed models for each group and variable identified significant improvements in the Youth group in maximal speed (30-40 m split), broad jump, countermovement jump, and final velocity30-15IFT (p ≤ 0.002), and a decrease in squat jump height with increasing age (p = 0.04). The Senior group recorded slower 10 m sprint time and a decrease in squat jump height with increasing age (p < 0.001). Body mass increased from 12 to 34 years old (Youth and Senior: p ≤ 0.001). The Youth group significantly differed in the rate of change compared to the Senior group in body mass, 10 m sprint time, countermovement jump, squat jump, and final velocity30-15IFT (p ≤ 0.001). This information can be used to identify average rates of physical performance improvement and decay to help guide optimal physical training and maximize the longevity of a female soccer players' career. 



#2 The Effect of Coach Feedback and Awareness of Head Impact Exposure on Practice Structure in Youth Football

Reference: J Neurotrauma. 2021 Jan 4. doi: 10.1089/neu.2020.7224. Online ahead of print. 

Authors: Daniella M DiGuglielmo, Gabriella M Milef, Justin B Moore, Mireille E Kelley, Alexander K Powers, Joel D Stitzel, Jillian E Urban

Summary: With the concern of concussion risk and repetitive head impacts in youth football, organizations have adopted rules that limit contact during practice. However, rule changes are not ubiquitous among organizations and are challenging to monitor and enforce. Ultimately, football practice activities are determined by coaches, but it is unknown whether providing objective data to coaches relating activities to their athletes' head impact exposure (HIE) would alter practice structure or help reduce HIE. This study evaluated the effect of coach awareness of HIE on practice structure over time. Head impact data from three intervention (56 players) and control (38 players) teams were collected over two youth football seasons. Athletes were instrumented with the Head Impact Telemetry (HIT) System and time-synchronized video was recorded for practices and games. Impact frequencies and head accelerations were compiled into weekly HIE practice and game reports shared with the head coach of each intervention team. Time per drill, impact rate, and impact magnitude were compared among three time frames (pre-season, mid-season, and late-season) using generalized linear models. Control teams had higher impact rates than intervention teams in all drills across time frames. Among all teams, 95th percentile linear and rotational accelerations were highest during mid-season. Among intervention teams, more time was spent on scrimmage and skill development from pre-season to late-season, with less time spent on tackling. This study suggests receiving objective data informing HIE in practice may contribute to changes in practice structure and help inform intervention efforts to improve head impact safety in football. 



#3 Injury and illness epidemiology in professional Asian football: lower general incidence and burden but higher ACL and hamstring injury burden compared with Europe

Reference: Br J Sports Med. 2021 Jan 5;bjsports-2020-102945. doi: 10.1136/bjsports-2020-102945. 

Authors: Montassar Tabben, Cristiano Eirale, Gurcharan Singh, Abdulaziz Al-Kuwari, Jan Ekstrand, Hakim Chalabi, Roald Bahr, Karim Chamari

Summary: While football injury and illness epidemiology surveillance at professional club level in Europe is available, epidemiological data from other continents are lacking. The aim was to investigate injury and illness epidemiology in professional Asian football. Professional teams from the Asian Football Confederation (AFC) league were followed prospectively for three consecutive AFC seasons (2017 through 2019, 13 teams per season, 322 team months). Time-loss injuries and illnesses in addition to individual match and training exposure were recorded using standardised digital tools in accordance with international consensus procedures. In total, 232 665 hours of exposure (88.6% training and 11.4% matches) and 1159 injuries were recorded; 496 (42.8%) occurred during matches, 610 (52.6%) during training; 32 (2.8%) were reported as 'not applicable' and for 21 injuries (1.8%) information was missing. Injury incidence was significantly greater during match play (19.2±8.6 injuries per 1000 hours) than training (2.8±1.4, p<0.0001), resulting in a low overall incidence of 5.1±2.2.The injury burden for match injuries was greater than from training injuries (456±336 days per 1000 hours vs 54±34 days, p<0.0001). The two specific injuries causing the greatest burden were complete ACL ruptures (0.14 injuries (95% CI 0.9 to 0.19) and 29.8 days lost (29.1 to 30.5) per 1000 hours) and hamstring strains (0.86 injuries (0.74 to 0.99) and 17.5 days (17.0 to 18.1) lost per 1000 hours).Reinjuries constituted 9.9% of all injuries. Index injuries caused 22.6±40.8 days of absence compared with 25.1±39 for reinjuries (p=0.62). The 175 illnesses recorded resulted in 1.4±2.9 days of time loss per team per month. Professional Asian football is characterised by an overall injury incidence similar to that reported from Europe, but with a high rate of ACL ruptures and hamstring injury, warranting further investigations. 



#4 Convergent Validity of CR100-Based Session Ratings of Perceived Exertion in Elite Youth Football Players of Different Ages 

Reference: Int J Sports Physiol Perform. 2021 Jan 6;1-5. doi: 10.1123/ijspp.2020-0047. Online ahead of print. 

Authors: Fabio R Serpiello, Will G Hopkins 

Summary: The purpose was to assess the convergent validity of internal load measured with the CR100 scale in youth football players of 3 age groups. A total of 59 players, age 12-17 years, from the youth academy of a professional football club were involved in this study. Convergent validity was examined by calculating the correlation between session ratings of perceived exertion (sRPE) and Edwards load, a commonly used load index derived from the heart rate, with the data originating from 1 competitive season. The magnitude of the relationship between sRPE and Edwards load was obtained with weighted mean correlations and by assessing the effect of the change of the Edwards load on sRPE. Differences between the individuals' intercepts and slopes were assessed by interpreting the SD representing the random effects (player identity and the interaction of player identity and scaled Edwards load). Probabilistic decisions about true (infinite sample) magnitudes accounting for sampling uncertainty were based on 1-sided hypothesis tests of substantial magnitudes, followed by reference Bayesian analysis. Very high relationships exist between the sRPE and Edwards load across all age groups, with no meaningful differences in the magnitudes of the relationships between groups. Moderate to large differences between training sessions and games were found in the slopes of the relationships between the sRPE and Edwards load in all age groups. Finally, mostly small to moderate differences were observed between individuals for the intercepts and slopes of the relationships between the sRPE and Edwards load. Practitioners working in youth team sports can safely use the CR100 scale to track internal load. 



#5 Experiences and Strategies Influencing Older Adults to Continue Playing Walking Football 

Reference: J Aging Phys Act. 2021 Jan 7;1-13. doi: 10.1123/japa.2020-0058. Online ahead of print. 

Authors: Rachel Cholerton, Helen Quirk, Jeff Breckon, Joanne Butt 

Summary: Adults aged 55+ years are most likely to be inactive, despite research suggesting that older adults experience multiple benefits when participating in physical activity and sport. Limited research focuses on long-term continuation of sport participation in this population, especially in "adapted sports" like walking football. This study explored the experiences of walking football maintenance in 55- to 75-year-old players. Semistructured interviews were conducted, with 17 older adults maintaining walking football play over 6 months. The inductive analysis revealed five higher-order themes representing maintenance influences and two higher-order themes relating to maintenance mechanisms (i.e., the conscious process by which players maintain). Influences when maintaining walking football included individual- and culture-level influences (e.g., perceived benefits of maintenance and ability acceptance). Maintenance mechanisms included cognitions and behaviors (e.g., scheduling sessions and redefining physical activity expectations). Findings highlight novel implications for policy and practice, which are important to consider when delivering walking football to older adults. 



#6 Upper-Body Resistance Training Following Soccer Match Play: Compatible, Complementary, or Contraindicated?

Reference: Int J Sports Physiol Perform. 2021 Jan 13;1-11. doi: 10.1123/ijspp.2020-0762. Online ahead of print. 

Authors: Angelo Sabag, Ric Lovell, Neil P Walsh, Nick Grantham, Mathieu Lacome, Martin Buchheit 

Summary: During heavily congested schedules, professional soccer players can experience exacerbated fatigue responses, which are thought to contribute to an increased risk of injury. Given that match-induced residual fatigue can last up to 72 hours, many coaches naturally prioritize recovery in the days immediately following match day. While it is intuitive for coaches and training staff to decrease the amount of auxiliary training practices to focus on recovery, prescribing upper-body resistance training on the day after match play has recently emerged as a specific training modality in this context. While these sessions may be implemented to increase training stimulus, there are limited data available regarding the efficacy of such a practice to improve recovery kinetics. In this narrative review, the authors look at the theoretical implications of performing upper-body resistance training on the day after match play on the status of various physiological and psychological systems, including neuromuscular, metabolic, hormonal, perceptual, and immunological recovery. The available evidence suggests that in most cases this practice, as currently implemented (ie, low volume, low intensity), is unlikely to be complementary (ie, does not accelerate recovery) but is potentially compatible (ie, does not impair recovery). Overall, because the perception of such sessions may be player dependent, their programming requires an individualized approach and should take into account match dynamics (eg, fixture scheduling, playing time, travel). 



#7 The Risk of Knee Osteoarthritis in Professional Soccer Players 

Reference: Dtsch Arztebl Int. 2021 Jan 1;118(1):arztebl.m2021.0007. doi: 10.3238/arztebl.m2021.0007. 

Authors: Alice Freiberg, Ulrich Bolm-Audorff, Andreas Seidler 

Summary: We address the question whether professional soccer players with and without macroinjury of the knee joint are at an elevated risk for knee osteoarthritis. A systematic review with meta-analyses was conducted. The study protocol was prospectively registered (registration number CRD42019137139). The MEDLINE, EMBASE, and Web of Science databases were searched for relevant publications; in addition, forward searching was performed, and the listed references were considered. All steps of the process were undertaken independently by two reviewers, and any discordances were resolved by consensus. For all publications whose full text was included, the methods used were critically evaluated. The quality of the evidence was judged using the GRADE criteria. The pooled odds ratio for objectively ascertained osteoarthrosis of the knee was 2.25 (95% confidence interval [1.41-3.61], I2 = 71%). When only radiologically ascertained knee osteoarthrosis was considered, the odds ratio was 3.98 [1.34; 11.83], I2 = 58%). The pooled risk estimator in studies in which knee joint macroinjury was excluded was 2.81 ([1.25; 6.32], I2 = 71%). A marked association was found between soccer playing and knee osteoarthritis in male professional soccer players. For female professional soccer players, the risk of knee osteoarthritis could not be assessed because of the lack of data. Knee injuries seem to play an important role in the development of knee osteoarthritis in professional soccer players. 



#8 Analyzing the Magnitude of Interlimb Asymmetries in Young Female Soccer Players: A Preliminary Study 

Reference: Int J Environ Res Public Health. 2021 Jan 8;18(2):E475. doi: 10.3390/ijerph18020475. 

Authors: Javier Raya-González, Filipe Manuel Clemente, Daniel Castillo

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Summary: Although asymmetries in lower limbs have been linked with players' performance in male soccer players, literature that has been published addressing female soccer is scarce. Thus, the aim of this study was twofold: (i) describe the asymmetries of women soccer players during jumping, change-of-direction and range-of-motion tests; and (ii) test possible relationships between asymmetries and injury risk in female soccer players. Sixteen female players (15.5 ± 1.5 years) performed a battery of fitness tests (i.e., jump ability, change-of-direction ability and passive range-of-motion) and muscle mass analysis via dual-energy X-ray absorptiometry, through which the specific asymmetry index and the related injury risk were calculated. Significant (p < 0.05) lower asymmetries in the change-of-direction test were observed in comparison to those observed in jumping and range-of-motion tests; significant (p < 0.05) lower asymmetries in muscle mass were also reported compared to those found in the change-of-direction and countermovement jump tests. Additionally, increased injury risk for countermovement jump and hip flexion with extended knee range-of-motion (relating to asymmetry values) and for ankle flexion with flexed knee range-of-motion in both legs (relating to reference range-of-motion values), as well as increased individual injury risk values, were observed across all tests. These findings suggest the necessity to implement individual approaches for asymmetry and injury risk analyses. 



#9 Physical performance and perception of foot discomfort during a soccer-specific match simulation. A comparison of football boots

Reference: J Sports Sci. 2021 Jan 12;1-9. doi: 10.1080/02640414.2020.1856461. Online ahead of print. 

Authors: Katrine Okholm Kryger, Kumbirai Mutamba, Séan Mitchell, Stuart Charles Miller, Steph Forrester

Summary: Football boots are marketed with emphasis on a single key performance characteristic (e.g. speed). Little is known on how design parameters impact players' performance. This study investigated the impact of boot design on performance maintenance and perceived foot comfort during a 90-minute match simulation drill. Eleven male university football players tested two commercially available "sprint boots" known to generate significantly different plantar pressures (high=Boot H and low=Boot L) . Players completed a modified Soccer-specific Aerobic Field Test on a 3G pitch. Heart rate, rated perceived exertion and perceived foot discomfort were assessed for each 15-min interval. Power generation was assessed pre- and post-match simulation. A significantly higher mean heart rate was seen for Boot L in the 60th-75th and 75th-90th minute intervals (P = 0.017, P = 0.012 respectively). Perceived exertion did not differ between boots (P ≥ 0.302). Power generation significantly decreased in Boot H between pre- and post-match (P = 0.042). Both boots increased discomfort with significantly more plantar discomfort felt in the last 30 min in Boot H (75th min: P = 0.037; 90th min: P = 0.048). The results imply that a comfortable boot design may improve maintenance of performance during match-play. 



#10 The Association Between Training Load and Injury Risk in Elite Youth Soccer Players: a Systematic Review and Best Evidence Synthesis 

Reference: Sports Med Open. 2021 Jan 11;7(1):6. doi: 10.1186/s40798-020-00296-1. 

Authors: Sven Verstappen, Rogier M van Rijn, Rick Cost, Janine H Stubbe

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Summary: Injury risk in elite youth soccer players is high. Implementing an optimal training load is of utmost importance to reduce the risk of injuries. The aim was to conduct a systematic review and best evidence synthesis to explore the effects of internal and external training load on injury risk in elite youth soccer players. MEDLINE, Embase, Web of Science, CENTRAL, and CINAHL were searched up until 17 January 2020. Each article had to meet all of the following criteria: (1) the study population consisted of male elite youth soccer players aged between 12 and 21 years; (2) a longitudinal, prospective study design was used; (3) soccer-related injuries were registered (i.e., self-reported or by medical staff); (4) external and/or internal load parameters were described; and (5) the article was published in an English peer-reviewed scientific journal. The quality of the included articles was assessed using the Newcastle-Ottawa Quality Assessment Scale (NOS). A best evidence synthesis was performed to rank the level of evidence. Five studies (2 high quality, 3 low quality) were included. Best evidence synthesis highlighted that there was moderate evidence for (1) no association between 2-, 3-, and 4-week cumulative loads for total distance covered; (2) no association between 1-week workloads (sRPE × duration); and (3) no association between A:C workload ratios (4 weeks) and injury risk. For all other comparisons, only insufficient or conflicting evidence was found. There is a paucity of evidence for an association between internal and external training load parameters and injury risk in elite youth soccer players. 



#11 Effects of high-intensity interval training in men soccer player's physical fitness: A systematic review with meta-analysis of randomized-controlled and non-controlled trials

Reference: J Sports Sci. 2021 Jan 11;1-22. doi: 10.1080/02640414.2020.1863644. Online ahead of print. 

Authors: Filipe Manuel Clemente, Rodrigo Ramirez-Campillo, Fábio Yuzo Nakamura, Hugo Sarmento

Summary: This systematic review with meta-analysis (SRMA) was conducted to assess the effects of high-intensity interval training (HIIT) programmes on men soccer players' aerobic fitness (maximal oxygen uptake and aerobic performance), repeated sprint ability (RSA), vertical jump height (VJH), and linear sprinting time (ST). An electronic search yielded 1,714 articles, 33 of which were included in the present study. Meta-analyses revealed significant benefits of HIIT compared to controls in maximal oxygen uptake (p = 0.018), AP (p = 0.041), and RSA (p = 0.049). No significant effects were found in terms of ST (p = 0.080). The meta-analyses of non-controlled studies revealed significant improvements after HIIT in maximal oxygen uptake (p = 0.001), AP (p = 0.007), RSA (p = 0.001), and ST (p < 0.001). However, no significant improvements in VHJ were found (p = 0.063). Furthermore, no significant differences were found in sub-group analysis (comparisons between HIIT types). In conclusion, HIIT is effective for improving maximal oxygen uptake, AP, and RSA regardless of the HIIT type. For VHJ and ST outcomes, it seems reasonable to complement the HIIT since it might not be enough to achieve significant changes. 



#12 The Validity of an Updated Metabolic Power Algorithm Based upon di Prampero's Theoretical Model in Elite Soccer Players

Reference: Int J Environ Res Public Health. 2020 Dec 20;17(24):9554. doi: 10.3390/ijerph17249554. 

Authors: Cristian Savoia, Johnny Padulo, Roberto Colli, Emanuele Marra, Allistair McRobert, Neil Chester, Vito Azzone, Samuel A Pullinger, Dominic A Doran

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Summary: The aim of this study was to update the metabolic power (MP) algorithm (PV˙O2, W·kg-1) related to the kinematics data (PGPS, W·kg-1) in a soccer-specific performance model. For this aim, seventeen professional (Serie A) male soccer players (V˙O2max 55.7 ± 3.4 mL·min-1·kg-1) performed a 6 min run at 10.29 km·h-1 to determine linear-running energy cost (Cr). On a separate day, thirteen also performed an 8 min soccer-specific intermittent exercise protocol. For both procedures, a portable Cosmed K4b2 gas-analyzer and GPS (10 Hz) was used to assess the energy cost above resting (C). From this aim, the MP was estimated through a newly derived C equation (PGPSn) and compared with both the commonly used (PGPSo) equation and direct measurement (PV˙O2). Both PGPSn and PGPSo correlated with PV˙O2 (r = 0.66, p < 0.05). Estimates of fixed bias were negligible (PGPSn = -0.80 W·kg-1 and PGPSo = -1.59 W·kg-1), and the bounds of the 95% CIs show that they were not statistically significant from 0. Proportional bias estimates were negligible (absolute differences from one being 0.03 W·kg-1 for PGPSn and 0.01 W·kg-1 for PGPSo) and not statistically significant as both 95% CIs span 1. All variables were distributed around the line of unity and resulted in an under- or overestimation of PGPSn, while PGPSo routinely underestimated MP across ranges. Repeated-measures ANOVA showed differences over MP conditions (F1,38 = 16.929 and p < 0.001). Following Bonferroni post hoc test significant differences regarding the MP between PGPSo and PV˙O2/PGPSn (p < 0.001) were established, while no differences were found between PV˙O2 and PGPSn (p = 0.853). The new approach showed it can help the coaches and the soccer trainers to better monitor external training load during the training seasons. 



#13 Effects of Strength vs. Plyometric Training Programs on Vertical Jumping, Linear Sprint and Change of Direction Speed Performance in Female Soccer Players: A Systematic Review and Meta-Analysis

Reference: Int J Environ Res Public Health. 2021 Jan 6;18(2):E401. doi: 10.3390/ijerph18020401. 

Authors: Elena Pardos-Mainer, Demetrio Lozano, Marcelino Torrontegui-Duarte, Antonio Cartón-Llorente, Alberto Roso-Moliner

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Summary: The main purpose of this systematic review and meta-analysis was to compare the effects of strength training (ST) and plyometric training (PT) on vertical jump, linear sprint and change of direction (COD) performance in female soccer players. A systematic search of the PubMed, Web of Science, Google Scholar and SportDiscus databases revealed 12 studies satisfying the inclusion criteria. The inverse-variance random-effects model for meta-analyses was used. Effect sizes (ES) were represented by the standardized mean difference and presented alongside 95% confidence intervals (CI). The magnitude of the main effect was small to moderate (vertical jump (ES 0.53 (95% CI-0.11, 0.95), Z = 2.47 (p = 0.01); linear sprint (ES -0.66 (95% CI-2.03, -0.21), Z = 2.20 (p = 0.03); COD (ES -0.36 (95% CI-0.68, -0.03), Z = 2.17 (p = 0.03)). Subgroup analyses were performed (i.e., ST and PT duration, frequency, session duration and total number of sessions), revealing no significant subgroup differences (p = 0.12-0.88). In conclusion, PT provides better benefits than ST to improve vertical jump, linear sprint and COD performance in female soccer players. However, significant limitations in the current literature prevent assured PT and ST prescription recommendations being made. 






Influence of Size and Maturity on Injury in Young Elite Soccer Players

The purpose of this study was to investigate sports injuries in younger (U9–U11) and older (U12–U13) children playing soccer at an elite level, analysing potential anthropometric and maturity risk factors. 





Effect of a Shock Micro-Cycle on Biochemical Markers in University Soccer Players

This study aimed to examine various biochemical biomarkers changes during a shock micro-cycle in soccer players from a university team.





Latest research in football - week 11 - 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 Ordering sequential competitions to reduce order relevance: Soccer penalty shootouts

Reference: PLoS One. 2020 Dec 30;15(12):e0243786. doi: 10.1371/journal.pone.0243786. eCollection 2020. 

Authors: Nils Rudi, Marcelo Olivares, Aditya Shetty

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Summary: In sequential competitions, the order in which teams take turns may have an impact on performance and the outcome. Previous studies with penalty shootouts have shown mixed evidence of a possible advantage for the first shooting team. This has led to some debate on whether a change in the rules of the game is needed. This work contributes to the debate by collecting an extensive dataset of shootouts which corroborates an advantage for the first shooter, albeit with a smaller effect than what has been documented in previous research. To evaluate the impact of alternative ordering of shots, we model shootouts as a probability network, calibrate it using the data from the traditional ordering, and use the model to conduct counterfactual analysis. Our results show that alternating the team that shoots first in each round would reduce the impact of ordering. These results were in part developed as supplement to field studies to support the International Football Association Board's (IFAB) consideration of changing the shooting order. 



#2 Defining the Normal Spectrum of Electrocardiographic and Left Ventricular Adaptations in Mixed-Race Male Adolescent Soccer Players 

Reference: Circulation. 2021 Jan 5;143(1):94-96. doi: 10.1161/CIRCULATIONAHA.120.049740. Epub 2020 Dec 30. 

Authors: Aneil Malhotra, David Oxborough, Prashant Rao, Gherardo Finocchiaro, Harshil Dhutia, Vivek Prasad, Chris Miller, Bernard Keavney, Michael Papadakis, Sanjay Sharma

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#3 Putting the player first: A method to analyse and develop expert players performance in professional soccer

Reference: J Sports Sci. 2020 Dec 31;1-13. doi: 10.1080/02640414.2020.1864103. Online ahead of print. 

Authors: Eileen Gleeson, Seamus Kelly

Summary: The purpose of this paper is to present a player-centred performance analysis method as an effective mechanism to enhance expert players' performance in professional soccer. Data were collected through an application of a developed performance analysis method and subsequent unstructured interviews to explore participants' experience of the applied methodology. Grounded by an enactive perspective of human activity, the applied methodology foregrounds the player's intrinsic experience and places the player at the centre of the analysis and interpretation process. The sample included thirty professional soccer players with professional playing experience ranging from 2 years to 19 years and representing three professional teams. Using an interpretive data analysis approach results were considered from a methodological perspective concerning the core functions of a performance analysis method. Categories regarding performance analysis and performance development were highlighted. Findings demonstrate that adopting a player-centred approach to performance analysis in professional soccer provides advancement of the understanding of the collective performance of the expert player and may increase the opportunity for sustained learning. 



#4 Salivary Immunoendocrine and Self-report Monitoring Profiles across an Elite-Level Professional Football Season 

Reference: Med Sci Sports Exerc. 2020 Dec 23;Publish Ahead of Print. doi: 10.1249/MSS.0000000000002553.

Authors: Matthew Springham, Sean Williams, Mark Waldron, Anthony J Strudwick, Chris Mclellan, Robert U Newton 

Summary: This investigation examined the longitudinal changes and inter-relationships of salivary and self-report monitoring measures across a professional football season. Measures were collected bi-weekly from 18 senior professional male players across a six-week pre-season and eight five-week in-season mesocycles and analysed using a linear mixed-effects model. Analysis identified a small (P=0.003) cross-season suppression of salivary immunoglobulin-A, small reductions to salivary α-amylase (P=0.047) and salivary cortisol (P=0.007), and trivial changes to salivary testosterone (P>0.05). The testosterone:cortisol ratio typically responded inversely to changes in player workload. Self-report measures of fatigue (P=0.030), sleep quality (P=0.003) and muscle soreness (P=0.005) improved (ES=small) across the first half of the season. Fatigue and sleep measures were most consistently related to hormonal measures (R2 = 0.43 to 0.45). For these relationships, increases in cortisol were associated with compromised self-report responses, whereas increases in testosterone:cortisol were associated with improved responses. Non-linear relationships were identified for fatigue with immunoglobulin-A (P=0.017; ES=trivial) and testosterone (P=0.012; ES=trivial); for sleep quality with testosterone (P<0.001; ES=trivial); for muscle soreness with testosterone (P=0.012; ES=trivial) and for the self-report inventory sum with testosterone (P=0.027; ES=trivial). For these relationships, self-report responses were optimal at mean immunoglobulin-A and testosterone levels and very low levels (-2 SD) exerted the most compromising effects. Players can experience a chronic cross-season suppression of mucosal immunity. Salivary immunoglobulin-A, testosterone, cortisol and testosterone:cortisol measures relate to self-report measures of fatigue, sleep quality and muscle soreness. In-season reductions in testosterone, cortisol and testosterone:cortisol or increases in cortisol among elite football players could be used to indicate the need for reduced workload, which might lead to improved wellbeing. 



#5 The incidence and characteristics of purposeful heading in male and female youth football (soccer) within Australia

Reference: J Sci Med Sport. 2020 Dec 26;S1440-2440(20)30865-3. doi: 10.1016/j.jsams.2020.12.010.

Authors: Kerry Peek, Teale Vella, Tim Meyer, Florian Beaudouin, Marnee McKay

Summary: The aim was too quantify the incidence and characteristics of purposeful headers and unintentional head impacts during male and female youth football (soccer) games in Australia. Ten match-videos (total n=110) per playing age (under 13-20 males; under 13-17 females) from the 2019 National Premier League season were coded for purposeful headers and unintentional head impacts. Total headers and head impacts as well as incidence rate (IR) per 1000 match-hours for different match characteristics were calculated. Purposeful headers accounted for 99% (n=4615, IR:1618) of total head impacts. The IR of purposeful headers per 1000 match-hours was highest for under-15 males (IR:2117) and under-17 females (IR:2090) followed by under-20 males (IR:1761). Midfielders completed the most headers in all female age groups (mean IR:713) and under 13-14 males (mean IR:891), with defenders completing the most headers in under 15-20 males (mean IR:760). Heading duels accounted for 16% of total headers with most headers performed during free play (68%), throw-ins (15%), free kicks (12%) and corner kicks (5%). Only 57 head impacts (IR:20) were coded as unintentional head impacts resulting from being struck by the ball or opponent body part with 4 (IR:1.4) requiring medical attention. Heading is a complex skill. Given the propensity of youth players of all ages to purposefully head the ball, consideration should be given to coaching heading technique based on specific game scenarios for their playing position and age group. The findings of this study can be used to inform heading guidelines. 



#6 Comparison of multidirectional jump performance and lower limb passive range of motion profile between soccer and basketball young players 

Reference: PLoS One. 2021 Jan 7;16(1):e0245277. doi: 10.1371/journal.pone.0245277. eCollection 2021. 

Authors: Marta Domínguez-Díez, Daniel Castillo, Javier Raya-González, Silvia Sánchez-Díaz, María Soto-Célix, Tara Rendo-Urteaga, Ángel Lago-Rodríguez

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Summary: This study was performed aimed at comparing multidirectional bilateral and unilateral jump performance and passive range of motion (ROM) of lower limbs between soccer and basketball young players and evaluating associations between inter-limb ROM asymmetry and bilateral jump performance. A total of 67 young male athletes participated in this study, who were classified as soccer (n = 40; 15.55 ± 1.5 y; 1.76 ± 0.12 m; 58.15 ± 10.82 kg; 19.84 ± 2.98 kg·m2) and basketball (n = 27; 15.7 ± 1.66 y; 1.76 ± 0.12 m; 62.33 ± 16.57 kg; 19.84 ± 2.98 kg·m2) players. Participants were asked to perform bilateral and unilateral multidirectional jumps, and passive ROM of hip (flexion, extension and abduction), knee (flexion) and ankle (dorsiflexion) joints was also assessed. Significant between-group differences were observed for hip extension with flexed knee ROM in dominant (soccer: 142.43 ± 7.74°; basketball: 148.63 ± 8.10°) and non-dominant (soccer: 144.38 ± 8.36°; basketball: 148.63 ± 6.45°) legs; hip flexion with flexed knee ROM in dominant (soccer: 13.26 ± 4.71°; basketball: 9.96 ± 3.42°) and non-dominant (soccer: 12.86 ± 4.55°; basketball: 9.70 ± 3.62°) legs; and for the ratio of hip abduction (soccer: 1.02 ± 0.08; basketball: 0.97 ± 0.11). However, no significant between-group differences were observed for bilateral and unilateral jump capacity, or for inter-limb asymmetries (dominant vs. non-dominant leg). Finally, no associations were observed between ROM ratio (dominant vs. non-dominant leg) and bilateral jump performance. These findings lead to the suggestion that differences on passive ROM values in young male athletes may be sport-specific. Additionally, there seems to be need for the implementation of training strategies specifically aimed at improving bilateral or unilateral jump ability, or at diminishing inter limb passive ROM differences in order to improve multidirectional jump performance for neither soccer nor basketball youth male players. 



#7 Improving Soccer Knowledge From Computerized Game Diagrams: Benefits of Sequential Instructional Arrows 

Reference: Percept Mot Skills. 2021 Jan 5;31512520983083. doi: 10.1177/0031512520983083.

Authors: Ghazi Rekik, Yosra Belkhir, Mohamed Jarraya

Summary: In this study, we used Cognitive Load Theory to examine the role of a sequential versus simultaneous presentation technique for learning tactical skills from computerized diagrams of soccer scenes with two levels of complexity. Young soccer players learned the evolution of soccer game systems from computer-based diagrams with three types of instructional arrows: simultaneous, sequential-without-tracing, and sequential-with-tracing. We randomly assigned participants to one of six experimental conditions (three arrow presentation methods by two levels of soccer scene complexity) and asked them to rate their invested mental efforts, complete a recall-reconstruction test, and indicate their attitudes, immediately after the learning phase. When diagram content complexity was low, the three types of arrow presentations had similar learning effects. However, when diagram content complexity was high, the two sequential means of presenting instructional arrows produced better learning outcomes (with a clear relative advantage for the sequential-with-tracing presentation). We also found that the sequential presentation of arrows elicited more positive player attitudes whatever the level of content complexity. Considering the better learning outcomes and improved player attitudes from sequential diagram presentations, soccer coaches should present computer-based instructional diagram arrows sequentially, rather than simultaneously. A sequential-with-tracing arrow presentation was particularly beneficial for learning complex team sport scenes. 



#8 The effect of a weekly flywheel resistance training session on elite U-16 soccer players' physical performance during the competitive season. A randomized controlled trial 

Reference: Res Sports Med. 2021 Jan 5;1-15. doi: 10.1080/15438627.2020.1870978. Online ahead of print. 

Authors: Javier Raya-González, Daniel Castillo, Kevin L de Keijzer, Marco Beato

Summary: This study investigated the effects of a weekly flywheel resistance training session over a 10-week period on U16 soccer players' physical performance with special attention to change of direction ability (e.g., deficit [CODdef]). Twenty elite young soccer players were assigned to an experimental (EG, n = 10) or control (CG, n = 10) group. Unilateral countermovement jumps with dominant (CMJd) and non-dominant (CMJnd) leg, 10, 20, and 30-m linear sprint test and change of direction sprint test in 5 + 5 (COD10) and 10 + 10 m (COD20) were performed before and after flywheel training period. Significant within-group differences were found in CG in COD10 (p = 0.01; effect size [ES] = large) and CODdef10 (p = 0.03; ES = small) with dominant leg, while differences in EG were observed in CMJ (p = 0.001-0.01; ES = moderate-large) and in all COD and CODdef variables (p = 0.001-0.04; ES = large). Between-groups analysis revealed differences in favour of the EG in CMJ (p = 0.03-0.05) and COD and CODdef variables (p = 0.001-0.05). These findings suggest a weekly flywheel training session is suitable for improving jumping and COD abilities in U16 elite soccer players in season. 



#9 Effectiveness of Plyometric and Eccentric Exercise for Jumping and Stability in Female Soccer Players-A Single-Blind, Randomized Controlled Pilot Study 

Reference: Int J Environ Res Public Health. 2021 Jan 3;18(1):294. doi: 10.3390/ijerph18010294. 

Authors: Guillermo Porrati-Paladino, Rubén Cuesta-Barriuso

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Summary: Hamstring muscle injury is common in female soccer players. Changes affecting eccentric strength, flexibility, and the quadriceps-hamstring contraction cycle are risk factors associated with this type of injury. Seventeen soccer players were randomized to two groups: experimental (plyometric and eccentric exercises without external loads) and control (eccentric exercises without external loads). Eighteen sessions were scheduled over 6 weeks. The exercise program included three plyometric exercises (single-leg squat and lunge, 180 jump, and broad jump stick landing) and three eccentric exercises (Nordic hamstring exercise, diver, and glider). Dependent variables were jumping height (My Jump 2.0 App) and anterior, posteromedial, and posterolateral lower limb stability (Y-Balance test). Following intervention, improvements were found in anterior and posteromedial stability (p = 0.04) in the experimental group. Posterolateral stability improved in athletes included in the control group (p = 0.02). There were differences in the repeated measures analysis for all variables, with no changes in group interaction (p > 0.05). Eccentric exercises, either combined with plyometric exercises or alone, can improve lower limb stability. No changes in jump height were noted in either group. There were no differences between the two groups in the variables studied. Future studies should analyze the effect of external loads on jumping stability and height in the performance of plyometric exercises. 



#10 Sustained Passing Performance of Elite and Subelite Female Soccer Players Following a Female Match-Specific Exercise Protocol

Reference: Int J Sports Physiol Perform. 2021 Jan 4;1-7. doi: 10.1123/ijspp.2020-0082. Online ahead of print. 

Authors: Mikayla J Lyons, Jennifer Conlon, Amy Perejmibida, Paola Chivers, Christopher Joyce 

Summary: This study examined the maintenance of passing performance following soccer-specific high-intensity intermittent exercise in elite (n = 9) and subelite (n = 11) Western Australian female soccer players (19.5 [2.5] y). A total of 20 participants completed the Loughborough Soccer Passing Test (LSPT) prior to, during, and following 90 minutes of a modified, female-specific, individualized exercise protocol (Loughborough Intermittent Shuttle Test [LIST]) to simulate 2 halves of a soccer match. Performance in the LSPT was calculated by adding "raw time" to the accumulated "penalty time" for each test. Elite players recorded greater distances (t58 = 4.671, P < .001, effect size [ES] = 1.21) and higher derived VO2max values (t58 = 4.715, P < .001, ES = 1.20) for the LIST exercise protocol over the subelite players. The total performance times for each LSPT were longer in the subelites in comparison with the elites, with a very large ES difference seen in post-LIST1 (t18 = -6.64, P < .001, ES = 2.99) and post-LIST2 (t18 = -9.143, P < .001, ES = 4.12). No between-groups differences were identified for "raw time" at any time point. Hence, all reported LSPT performance differences are attributed to "penalty time." These data suggest that elite players can sustain their passing performance more efficiently throughout match play that can subelite female soccer players. These findings may contribute to future talent-identification testing by helping to distinguish between elite- and subelite-level players through sustained passing performance. Coaches may also use this information to better inform best-practice training methods through modification of male soccer-specific high-intensity intermittent exercise to a female cohort. 



#11 Morning Priming Exercise Strategy to Enhance Afternoon Performance in Young Elite Soccer Players

Reference: Int J Sports Physiol Perform. 2021 Jan 5;1-8. doi: 10.1123/ijspp.2020-0094. Online ahead of print. 

Authors: Federico Donghi, Ermanno Rampinini, Andrea Bosio, Maurizio Fanchini, Domenico Carlomagno, Nicola A Maffiuletti 

Summary: The purpose was to compare the effects of different modalities of morning priming exercise on afternoon physical performance with the associated hormonal and psychophysiological responses in young soccer players. In a randomized counterbalanced crossover design, 12 young soccer players completed 3 different morning conditions on 3 different days: repeated-sprint running (6 × 40 m), easy exercise (4 × 12 fast half squats, 6 speed ladder drills, and 20-m sprints), and control (no exercise). Blood testosterone and cortisol concentrations were assessed upon arrival (approximately 8:30AM) and approximately 5 hours and 30 minutes later. Body temperature, self-reported mood, quadriceps neuromuscular function (maximal voluntary contraction, voluntary activation, rate of torque development, and twitch contractile properties), jump, and sprint performance were evaluated twice per day, while rating of perceived exertion, motivation, and the Yo-Yo Intermittent Recovery level 2 (IR2) tests were assessed once per day. Compared with the control, repeated-sprint running induced a possible positive effect on testosterone (+11.6%) but a possible to very likely negative effect on twitch contractile properties (-13.0%), jump height (-1.4%), and Yo-Yo IR2 (-7.1%). On the other hand, easy exercise had an unclear effect on testosterone (-3.3%), resulted in lower self-reported fatigue (-31.0%) and cortisol (-12.9%), and had a possible positive effect on the rate of torque development (+4.3%) and Yo-Yo IR2 (+6.5%) compared with the control. Players' testosterone levels were positively influenced by repeated-sprint running, but this did not translate into better physical function, as both muscular and endurance performance were reduced. Easy exercise seemed to be suitable to optimize the physical performance and psychophysiological state of young soccer players. 



#12 Monitoring Practices of Training Load and Biological Maturity in UK Soccer Academies 

Reference: Int J Sports Physiol Perform. 2021 Jan 5;1-12. doi: 10.1123/ijspp.2019-0624. Online ahead of print. 

Authors: Jamie Salter, Mark B A De Ste Croix, Jonathan D Hughes, Matthew Weston, Christopher Towlson 

Summary: Overuse injury risk increases during periods of accelerated growth, which can subsequently impact development in academy soccer, suggesting a need to quantify training exposure. Nonprescriptive development scheme legislation could lead to inconsistent approaches to monitoring maturity and training load. Therefore, this study aimed to communicate current practices of UK soccer academies toward biological maturity and training load. Forty-nine respondents completed an online survey representing support staff from male Premier League academies (n = 38) and female Regional Talent Clubs (n = 11). The survey included 16 questions covering maturity and training-load monitoring. Questions were multiple-choice or unipolar scaled (agreement 0-100) with a magnitude-based decision approach used for interpretation. Injury prevention was deemed highest importance for maturity (83.0 [5.3], mean [SD]) and training-load monitoring (80.0 [2.8]). There were large differences in methods adopted for maturity estimation and moderate differences for training-load monitoring between academies. Predictions of maturity were deemed comparatively low in importance for bio-banded (biological classification) training (61.0 [3.3]) and low for bio-banded competition (56.0 [1.8]) across academies. Few respondents reported maturity (42%) and training load (16%) to parent/guardians, and only 9% of medical staff were routinely provided this data. Although consistencies between academies exist, disparities in monitoring approaches are likely reflective of environment-specific resource and logistical constraints. Designating consistent and qualified responsibility to staff will help promote fidelity, feedback, and transparency to advise stakeholders of maturity-load relationships. Practitioners should consider biological categorization to manage load prescription to promote maturity-appropriate dose-responses and to help reduce the risk of noncontact injury. 



#13 Detrimental Effects of the Off-Season in Soccer Players: A Systematic Review and Meta-analysis 

Reference: Sports Med. 2021 Jan 5. doi: 10.1007/s40279-020-01407-4. Online ahead of print. 

Authors: Filipe Manuel Clemente, Rodrigo Ramirez-Campillo, Hugo Sarmento

Summary: The off-season period in soccer leads necessarily to changes in fitness status. However, there is a lack of systematization that allows identifying the magnitude of these changes in groups participating in off-season training programs compared with those subjected to training cessation. This systematic review with meta-analysis was conducted to assess the effects of training cessation in off-season training programs on men soccer players' body fat, maximal oxygen uptake (VO2max), yo-yo intermittent recovery test (YYIRT), vertical jump, sprinting time, and repeated-sprint ability. To qualify for inclusion in the systematic review, studies must have included: (1) a detraining period of ≥ 2 weeks; (2) controlled trials or cohorts of healthy men soccer players with no restriction on age; and (3) a pre-post training cessation or off-season training programs measure of body fat (%), VO2max (mL kg-1 min-1), YYIRT performance (meters), vertical jump (height), sprinting (time), and repeated-sprint ability (total time). The electronic search yielded 563 articles, and 12 were subsequently included. Significant (all p < 0.05) detrimental training cessation effects were noted for body fat (ES = 0.26), VO2max (ES = - 1.48), YYIRT (ES = - 0.46), vertical jump (ES = - 0.81), and repeated-sprint ability (ES = 0.68). Similarly, significant (all p < 0.05) detrimental off-season training programs effects were noted for body fat (ES = 0.26), VO2max (ES = - 0.48), vertical jump (ES = - 0.51), and sprinting time (ES = 0.86). When training cessation and off-season training programs effects were compared, greater detrimental effects were noted after training cessation for VO2max (p = 0.002) and repeated-sprint ability (p < 0.001). Detrimental effects on body composition and physical fitness were observed after both training cessation and off-season training programs. However, off-season training programs seem to ameliorate such detrimental effects on VO2max and repeated-sprint ability to some extent. The results presented here call for the implementation of more effective off-season training programs among male soccer players. 



#14 COVID-19-Related Restrictions and Quarantine COVID-19: Effects on Cardiovascular and Yo-Yo Test Performance in Professional Soccer Players 

Reference: Front Psychol. 2020 Dec 18;11:589543. doi: 10.3389/fpsyg.2020.589543. eCollection 2020. 

Authors: Lucas de Albuquerque Freire, Márcio Tannure, Márcio Sampaio, Maamer Slimani, Hela Znazen, Nicola Luigi Bragazzi, Esteban Aedo-Muñoz, Dany Alexis Sobarzo Soto, Ciro José Brito, Bianca Miarka 

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Summary: The present study aimed to verify the quarantine's effects during a serious viral outbreak on the cardiovascular and performance associated with the Yo-Yo test in a sample of professional soccer players. 20 high-level soccer players (n = 20; age: 26 ± 4 years-old; weight: 76.85 ± 6.7 kg; height: 179 ± 6 cm) participated in this study. The intermittent Yo-Yo test was performed pre- and post- COVID-19 quarantine in a random order. During each test, the soccer players' running performance outcomes were monitored using a portable 5-Hz GPS with a 100 Hz accelerometer and a paired t-test was conducted at a p-value of ≤ 0.05. The main results demonstrated significant differences between pre- versus post-COVID-19 quarantine in the following variables: relative distance (161.7 ± 5.9 > 141.1 ± 33.8 m/min), maximal speed (18.7 ± 0.9 > 18.2 ± 0.6 km/h), acceleration (60 ± 20 frequency > 52 ± 16 frequency), deceleration (34 ± 13 frequency > 27 ± 6 frequency), sprints > 19 km/h [0.8 (0.2;3)% >0.5 (0;0.5)%], and in high intensity running distance [16.48 (2.68;41.64)m > 0.827 (0.164;3.0)m]. We concluded that COVID-19-related restrictions and quarantine COVID-19 demonstrated adverse effects on professional soccer players' Yo-Yo tests performance. 






Effects of Mental Fatigue in Total Running Distance and Tactical Behaviour During Small-Sided Games

Mental fatigue can impact physical demands and tactical behaviour in sport-related contexts. Small-sided games (SSGs) are often used to develop a specific sport-related context. This systematic review (with a meta-analysis) was conducted to compare the effects of mental fatigue vs. control conditions in terms of the total running distance and tactical behaviour of soccer players during SSGs.





Selected, Deselected and Reselected: A Case Study Analysis of Attributes Associated With Player Reselection Following Closure of a Youth Soccer Academy

Considering the perceived benefit of early recruitment and the time and resources spent developing youth players, individuals released from talent development programmes are often re-recruited by rival academies. Limited data exists on players deselected from (or reselected to) youth soccer academies.





Latest research in football - week 10 - 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 Intra and inter-tester reliability of a novel device to assess gluteal muscle strength in professional football players

Reference: Res Sports Med. 2020 Dec 30;1-13. doi: 10.1080/15438627.2020.1868466. Online ahead of print. 

Authors: V Moreno-Pérez, M Beato, J Del Coso, J L Hernández-Davó, A Sole, M Peñaranda-Moraga, M Madruga-Parera, D Romero-Rodríguez

Summary: The aim of this study is to investigate inter-tester and intra-tester reliability of a novel clam test (CLAMT) for the measurement of gluteal muscle strength and to detect possible differences between CLAMT values in football players with and without a history of groin injuries. Twenty male football players participated in the test-retest and sixty-two male professional football players participated in the case-control study. Hip abductor maximal muscle strength was evaluated either using CLAMT or in a supine position with the hip in a neutral pose. For CLAMT, intraclass correlation coefficient (ICC) for inter-tester-intra-day reliability was 0.80 (95% CI: 0.60-0.90), with a standard error of measurement of 34.2 N. The intra-tester-intra-day ICC was 0.92 (95% CI: 0.87-0.95), with a standard error of measurement of 23.6 N. The inter-week ICC was 0.96 (95% CI: 0.92-0.98), with a standard error of measurement of 18.9 N. CLAMT showed lower (but not significant) strength values in football players with a history of groin injuries to non-injured players. CLAMT showed good to excellent levels of reliability, intraday and inter-week, with low standard errors of measurement while it was effective (possible) to identify residual weakness in players with previous groin injuries. 



#2 Assessment of Biomechanical Response to Fatigue through Wearable Sensors in Semi-Professional Football Referees 

Reference: Sensors (Basel). 2020 Dec 24;21(1):E66. doi: 10.3390/s21010066. 

Authors: Luigi Truppa, Michelangelo Guaitolini, Pietro Garofalo, Carlo Castagna, Andrea Mannini

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Summary: Quantifying muscle fatigue is a key aspect of everyday sport practice. A reliable and objective solution that can fulfil this task would be deeply important for two main reasons: (i) it would grant an objective indicator to adjust the daily training load for each player and (ii) it would provide an innovative tool to reduce the risk of fatigue-related injuries. Available solutions for objectively quantifying the fatigue level of fatigue can be invasive for the athlete; they could alter the performance or they are not compatible with daily practice on the playground. Building on previous findings that identified fatigue-related parameters in the kinematic of the counter-movement jump (CMJ), this study evaluates the physical response to a fatigue protocol (i.e., Yo-Yo Intermittent Recovery Test Level 1) in 16 football referees, by monitoring CMJ performance with wearable magneto-inertial measurement units (MIMU). Nineteen kinematic parameters were selected as suitable indicators for fatigue detection. The analysis of their variations allowed us to distinguish two opposites but coherent responses to the fatigue protocol. Indeed, eight out of sixteen athletes showed reduced performance (e.g., an effective fatigue condition), while the other eight athletes experienced an improvement of the execution likely due to the so-called Post-Activation Potentiation. In both cases, the above parameters were significantly influenced by the fatigue protocol (p < 0.05), confirming their validity for fatigue monitoring. Interesting correlations between several kinematic parameters and muscular mass were highlighted in the fatigued group. Finally, a "fatigue approximation index" was proposed and validated as fatigue quantifier. 



#3 Technical match actions and plasma stress markers in elite female football players during an official FIFA Tournament 

Reference: Scand J Med Sci Sports. 2020 Dec 29. doi: 10.1111/sms.13878. Online ahead of print. 

Authors: Susana Póvoas, António Ascensão, Josė Magalhães, Pedro Silva , Håvard Wiig, Truls Raastad, Carlo Castagna, Helena Andersson 

Summary: This study analyzed the impact of performing four consecutive football matches separated by 48-72 hours during a FIFA tournament on physical load, technical performance and plasma markers of redox state, muscle damage and inflammation in elite female players. Forty-eight players from three national teams were evaluated at seven time points: before (baseline) and throughout the tournament (after each match and before two training sessions). Only data from players who played all matches were included in the analyses (N = 13). The players were divided into high-rank (N = 6) and low-rank (N = 7) team players according to FIFA standards. Plasma creatine kinase (CK), C-reactive protein (CRP), total antioxidant status (TAS), and uric acid (UA) were analyzed at the selected time points. Technical performance and physical load were also quantified according to team rank. Players from low-rank teams played significantly more time than high-rank players (85 ± 10 vs 67 ± 15 minutes; P = .02; d = 1.51). Low-rank team players presented higher values in technical performance actions than the high-rank team players, but most of the differences were explained by the longer match time played. UA content differed across the matches, increasing from baseline (F(4,40) = 3.90; P = .01) and more in the high-rank team players (F(1,10) = 20.46; P = .001), while CRP only differed across the matches (F(4,36) = 2.66; P = .05), also increasing from baseline. A large time effect was shown for UA only in the high-rank players (η2 p = 0.50; P = .02). Four consecutive matches did not result in considerable alterations in plasma stress markers, physical load, and technical performance in elite female football players from distinct rank levels. 



#4 Delayed peroneal muscle reaction time in male amateur footballers during a simulated prolonged football protocol 

Reference: Res Sports Med. 2020 Dec 29;1-9. doi: 10.1080/15438627.2020.1868467. Online ahead of print. 

Authors: Wei Sun, Edwin C H Chan, Daniel T P Fong

Summary: Peroneal muscle fatigue could result in ankle inversion sprain injuries. This study investigated the peroneal muscle reaction time during a simulated prolonged football protocol. Nine male footballers completed a 105-minute simulated prolonged football protocol. The peroneal muscle reaction time to an ankle inversion perturbation was measured every 15 minutes by a surface electromyography system sampling at 1000 Hz. One-way repeated ANOVA with post-hoc paired t-test showed a steady upward trend starting from 48.9 ms at baseline to 57.1 ms at the end of the first half, followed by a recovery back to 50.9 ms at the start of the second half and a further delay in the last 30 minutes to 60.2 ms at the end of the protocol. Delayed peroneal muscle reaction was found after 30 minutes of the first half and 15 minutes of the second half of a football match. The risk of ankle sprain could increase in the latter minutes in each half protocol. Thus, prevention injury training strategies should focus on these specific durations in football matches. 



#5 The Football Association Injury and Illness Surveillance Study: The Incidence, Burden and Severity of Injuries and Illness in Men's and Women's International Football 

Reference: Sports Med. 2020 Dec 28;1-20. doi: 10.1007/s40279-020-01411-8. Online ahead of print. 

Authors: Bradley Sprouse, Jon Alty, Steve Kemp, Charlotte Cowie, Ritan Mehta, Alicia Tang, John Morris, Simon Cooper, Ian Varley  

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Summary: The aim was to determine the incidence and characteristics of injury and illness in English men's and women's senior and youth international football. Time-loss injuries and illnesses, alongside match and training exposure, were collected across 8 seasons (2012-2020) in youth (U15, U16, U17, U18, U19) and senior (U20, U21, U23, senior) English men's and women's international teams. Analysis of incidence, burden, and severity of injury and illness was completed. Sex-specific comparisons were made between the senior and youth groups, and across the 8 seasons of data collection. In men's international football, 535 injuries were recorded (216 senior; 319 youth) during 73,326 h of exposure. Overall, match injury incidence (31.1 ± 10.8 injuries/1000 h) and burden (454.0 ± 195.9 d absent/1000 h) were greater than training injury incidence (4.0 ± 1.0 injuries/1000 h) and burden (51.0 ± 21.8 d absent/1000 h) (both P < 0.001). In women's international football, 503 injuries were recorded (senior: 177; youth: 326) during 80,766 h of exposure and match injury incidence (27.6 ± 11.3 injuries/1000 h) and burden (506.7 ± 350.2 days absent/1000 h) were greater than training injury incidence (5.1 ± 1.8 injuries/1000 h) and burden (87.6 ± 32.8 days absent/1000 h) (both P < 0.001). In women's international football, a group × season interaction was observed for training injury incidence (P = 0.021), with the senior group recording a greater training injury incidence during the 2015-2016 season compared to the youth group (14.4 vs 5.7 injuries/1000 h; P = 0.022). There was no difference in injury severity between match and training for men's (P = 0.965) and women's (P = 0.064) international football. The findings provide a comprehensive examination of injury and illness in English men's and women's senior and youth international football. Practitioners will be able to benchmark their team's injury and illness incidence and characteristics to the match-play and training information provided in the present study. 



#6 Prospective Study of Muscle Injuries in Three Consecutive Seasons of the Brazilian Football Championship 

Reference: Rev Bras Ortop (Sao Paulo). 2020 Dec;55(6):687-694. doi: 10.1055/s-0040-1712988. Epub 2020 Sep 24. 

Authors: Gabriel Furlan Margato, Edilson Ferreira Andrade Júnior, Paulo Henrique Schmidt Lara, Jorge Roberto Pagura, Moisés Cohen, Gustavo Gonçalves Arliani

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Summary: The aim was to perform a prospective evaluation of muscle injuries that occurred during the matches of series A and B of the Brazilian Men's Football Championship from 2016 to 2018. A prospective-cohort study with data collection regarding muscle injuries that occurred during the official matches of the first and second divisions of the Brazilian Men's Soccer Championship in the 2016, 2017 and 2018 seasons. The total number of muscle injuries was of 577 throughout the 3 seasons, with a gradual and annual reduction in the incidence of injuries (219 injuries in 2016, 195 in 2017, and 163 in 2018), with a statistically significant difference between the 2016 and 2018 seasons. Muscle injuries represented approximately 35% of the total lesions. The incidence of muscle injuries was of 7.66 per 1,000 hours of play. During the 3 seasons (2016 to 2018), the most common injury was of the hamstring muscle (41.1%, 40.5%, and 33.7% respectively). Wingers were the most affected players, and the most common injury severity scale was moderate (8 to 28 days). The moment of the match with the highest incidence of injuries was in the period between 61 and 75 minutes, with an index of 19.9%, with no statistical difference in relation to the other periods of the match. There was an incidence of muscle injuries of 7.7 /1,000 h, and they occurred predominantly in home games, in defenders (wingers and centre-backs), with an average age of 28 years, mainly involving the hamstring muscles, with a moderate mean time of absence (8 to 28 days). 



#7 FIFA Sudden Death Registry (FIFA-SDR): a prospective, observational study of sudden death in worldwide football from 2014 to 2018

Reference: Br J Sports Med. 2020 Dec 23;bjsports-2020-102368. doi: 10.1136/bjsports-2020-102368.

Authors: Florian Egger, Jürgen Scharhag, Andreas Kästner, Jiří Dvořák, Philipp Bohm, Tim Meyer

Summary: The aim was to investigate the underlying causes and regional patterns of sudden death in football (soccer) players worldwide to inform and improve existing screening and prevention measures. From 2014 to 2018 cases of sudden cardiac death (SCD), survived sudden cardiac arrest (SCA) and traumatic sudden death were recorded by media monitoring (Meltwater), a confidential web-based data platform and data synchronisation with existing national Sudden Death Registries (n=16). Inclusion criteria were met when sudden death occurred during football-specific activity or up to 1 hour afterwards. Death during other activities was excluded. A total of 617 players (mean age 34±16 years, 96% men) with sudden death were reported from 67 countries; 142 players (23%) survived. A diagnosis by autopsy or definite medical reports was established in 211 cases (34%). The leading cause in players >35 years was coronary artery disease (76%) and in players ≤35 years was sudden unexplained death (SUD, 22%). In players ≤35 years the leading cause of SCD varied by region: cardiomyopathy in South America (42%), coronary artery anomaly in North America (33%) and SUD in Europe (26%). Traumatic sudden death including commotio cordis occurred infrequently (6%). Cardiopulmonary resuscitation (CPR) resulted in a survival rate of 85% with the use of an automated external defibrillator (AED) compared with 35% without. Regional variation in SCD aetiology should be verified by expansion of national registries and uniform autopsy protocols. Immediate access to an AED at training and competition sites, as well as CPR training for players, coaches and staff members, is needed to improve survival from SCA. 



#8 Injury patterns differ with age in male youth football: a four-season prospective study of 1111 time-loss injuries in an elite national academy 

Reference: Br J Sports Med. 2020 Dec 23;bjsports-2020-103430. doi: 10.1136/bjsports-2020-103430. 

Authors: Eirik Halvorsen Wik, Lorenzo Lolli, Karim Chamari, Olivier Materne, Valter Di Salvo, Warren Gregson, Roald Bahr

Summary: The purpose was to describe age group patterns for injury incidence, severity and burden in elite male youth football. Prospective cohort study capturing data on individual exposure and time-loss injuries from training and matches over four seasons (2016/2017 through 2019/2020) at a national football academy (U13-U18; age range: 11-18 years). Injury incidence was calculated as the number of injuries per 1000 hours, injury severity as the median number of days lost and injury burden as the number of days lost per 1000 hours. We included 301 players (591 player-seasons) and recorded 1111 time-loss injuries. Overall incidence was 12.0 per 1000 hours (95% CI 11.3 to 12.7) and burden was 255 days lost per 1000 hours (252 to 259). The mean incidence for overall injuries was higher in the older age groups (7.8 to 18.6 injuries per 1000 hours), while the greatest burden was observed in the U16 age group (425 days; 415 to 435). In older age groups, incidence and burden were higher for muscle injuries and lower for physis injuries. Incidence of joint sprains and bone stress injuries was greatest for players in the U16, U17 and U18 age groups, with the largest burden observed for U16 players. No clear age group trend was observed for fractures. Injury patterns differed with age; tailoring prevention programmes may be possible. 



#9 The Size and Prevalence of Bony Hip Morphology Does Not Differ Between Football Players With and Without Hip and/or Groin Pain: Findings From the FORCe Cohort 

Reference: J Orthop Sports Phys Ther. 2020 Dec 25;1-43. doi: 10.2519/jospt.2021.9622. Online ahead of print. 

Authors: Joshua Heerey, Rintje Agricola, Anne Smith, Joanne Kemp, Tania Pizzari, Matthew King, Peter Lawrenson, Mark Scholes, Kay Crossley

Summary: The aim was to compare the size and prevalence of bony hip morphology in football players' hips with and without hip and/or groin pain. 184 (290 hips; 20% women) football players (soccer and Australian football) with self-reported hip and/or groin pain (>6 months duration) and a positive FADIR test and 55 (110 hips; 25% women) control football players (no pain, negative FADIR) were recruited. For bony hip morphology, alpha angle and lateral-center-edge-angle (LCEA) were determined from anteroposterior pelvis and Dunn 45° radiographs. The alpha angle and LCEA were analyzed as continuous measures (size) and dichotomised using threshold values to determine the prevalence of bony hip morphology (cam, large cam, pincer and acetabular dysplasia). Regression analyses estimated differences in the size and prevalence of bony hip morphology between football players with and without pain. In all football players and in men, the size and prevalence of bony hip morphology did not differ between hips with and without hip and/or groin pain. In football players, cam morphology was evident in 63% hips without pain and 71% of hips with hip and/or groin pain. Women with hip and/or groin pain had larger alpha angle values than women without on the Dunn 45° view (5.9°; 95% CI: 1.2°, 10.6°, P = .014). The size and prevalence bony hip morphology appears similar in football players with and without hip and/or groin pain.



#10 Applying a holistic hamstring injury prevention approach in elite football: 12 seasons, single club study

Reference: Scand J Med Sci Sports. 2020 Dec 31. doi: 10.1111/sms.13913. Online ahead of print. 

Authors: Luis Suarez-Arrones, Fábio Yuzo Nakamura, Rafael A Maldonado, Nacho Torreno, Valter Di Salvo, Alberto Mendez-Villanueva

Summary: The aim was to investigate the preventive effect of a complex training program based on holistic hamstring health understanding in elite professional soccer players. This study involved an elite club in Europe and was conducted over 12 seasons. The last 2 seasons were the intervention period and the others were the control seasons. During the intervention period, players performed a complex program organized into different interventions throughout the week having as a priority the player health. Hamstring injuries, absenteeism, injury rates, and injury burden between the control and intervention seasons were compared using a rate ratio (RR) with 95% CI. Players had a mean exposure of 333.5±18.6 hours per season with no significant differences between the intervention and control seasons. The overall injury rate was 3 times lower during the two intervention seasons than during the previous seasons (p<0.01); the match injury rate was 2.7 times lower (p<0.01) and the training rate 4.3 times (p<0.01). Injury burden was almost 4 times lower during the two intervention seasons than during the previous seasons (p<0.01) and recurrences in the control group were 10% vs. 0% in the intervention group. Hamstring injuries were reduced ~3 times during the seasons in which elite football players were exposed to multicomponent, complex prevention training with individual approaches based on player needs, management of training load, individualized physiotherapy treatment, and planned staff communication, in comparison to the control seasons without a clearly defined and structured injury prevention intervention. 



#11 A four-week training program with the Nordic hamstring exercise during preseason increases eccentric strength of male soccer player

Reference: Int J Sports Phys Ther. 2020 Aug;15(4):571-578. 

Authors: Nathalia Trevisol de Oliveira, Thales Menezes Medeiros, Karoline Baptista Vianna, Gabriel Dos Santos Oliveira, João Breno de Araujo Ribeiro-Alvares, Bruno Manfredini Baroni

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Summary: The Nordic hamstring exercise (NHE) is an effective strategy to prevent hamstring strain injuries in soccer players. The current literature recommends a 10-week training program with three sessions per week, but the short preseason period and the congested schedule make difficult for high-performance soccer teams to apply the NHE as recommended. The purpose of this study was to examine the effect of a pragmatic NHE training program during a four-week preseason period on eccentric knee flexor strength of high-performance soccer players. This study included 25 under-20 male soccer players from a premier league club. They performed eight sessions of NHE (3 sets of 6-10 repetitions, twice a week) during the four-week preseason period. The eccentric knee flexor strength was evaluated during the NHE execution on a custom-made device, before and after the training program. The NHE training program significantly increased the players' eccentric knee flexor strength in both right (Δ = 13%; p<0.001; effect size = 0.97) and left limbs (Δ = 13%; p<0.001; effect size = 0.92). Individual analysis identified 76% of the players as responders to the NHE training program (Δ = 16%; effect size = 1.60), and 24% as non-responders (Δ = 3%; effect size = 0.24). A four-week training program with NHE performed twice a week is feasible in the real-world of high-performance soccer clubs and increases the eccentric knee flexor strength of male soccer players. 



#12 Association of Low Energy Availability and Suppressed Metabolic Status in Korean Male Collegiate Soccer Players: A Pilot Study

Reference: Am J Mens Health. Nov-Dec 2020;14(6):1557988320982186. doi: 10.1177/1557988320982186. 

Authors: Sihyung Lee, Moto Kuniko, Seungah Han, Taewoong Oh, Motoko Taguchi

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Summary: Low energy availability (EA) can impair physiological function in athletes. The purpose of this study was to investigate EA status, metabolic status, and bone metabolism with biochemical analysis in Korean male soccer players. Twelve male athletes (18-20 years) completed the study. Body composition and bone mineral density were measured using dual energy X-ray absorptiometry (DXA), while VO2 max was determined by an incremental exercise test. Blood samples were taken for bone marker and hormone analyses. Resting energy expenditure (REE) was measured using the Douglas bag method and predicted using the DXA method. Food diaries and heart rates (HR) during training were recorded, and the Profile of Mood States 2 and Eating Attitude Test 26 were completed. Group differences between low EA (LEA <30 kcal/kg FFM/d, n = 5) and high EA (HEA ≥30 kcal/kg FFM/d, n = 7) were evaluated. The mean EA of the all participants was 31.9 ± 9.8 kcal/kg FFM/d with only two participants having an EA above 45 kcal/kg FFM/d. LEA showed suppressed REE (LEA: 26.0 ± 1.7 kcal/kg/d, HEA: 28.8 ± 1.4 kcal/kg/d, p = .011) with a lower REEratio (LEA: 0.91 ± 0.06, HEA: 1.01 ± 0.05, p = .008) as well as a lower insulin-like growth factor 1 (IGF-1) level (LEA: 248.6 ± 51.2 ng/mL, HEA: 318.9 ± 43.4 ng/mL, p = .028) compared to HEA. There were no group differences in bone markers or other hormone levels. Korean male athletes exhibited low EA status with suppressed metabolism, but there was limited evidence on the effect of EA on bone metabolism, endocrine system, and psychological parameters. 



#13 Systematic review and meta-analysis of sex-based differences for concussion incidence in soccer 

Reference: Phys Sportsmed. 2021 Jan 7;1-9. doi: 10.1080/00913847.2020.1868955. Online ahead of print. 

Authors: Udit Dave, James Kinderknecht, Jennifer Cheng, Kristen Santiago, Bridget Jivanelli, Daphne I Ling

Summary: The purpose was to compare concussion incidence in male and female soccer players due to the specific concussion-causing activity. PubMed, EMBASE, and Cochrane Library were searched for studies published between January 2000 and February 2020. Search terms included 'sex,' 'gender,' 'sex differences,' 'brain injury,' 'sports,' 'athletes,' 'incidence,' 'epidemiology,' 'symptoms,' and 'injury rate.' Studies that contained data on concussion incidence in soccer and featured comparisons by sex and soccer activity were included. Studies that were not written in English, contained data on non-sports-related concussions, or were conference abstracts were excluded. Six studies were included in this meta-analysis, each of which contributed the number of concussions in males and females for a specific soccer activity. Concussion incidence rates were calculated using athlete-exposures as the denominator and a rate ratio was measured by dividing the concussion rate among female soccer players by the rate among male soccer players. Female soccer players were shown to have a greater rate of concussions from heading [1.65 (95% CI: 1.35, 2.03, p < 0.001)] and goalkeeping [1.63 (95% CI: 1.22, 2.17, p = 0.001)]. There were 3 studies comparing sex differences for general play. While the pooled rate ratio was statistically significant [1.51 (95% CI: 1.12, 2.04), p = 0.007], this result was largely driven by 1 study. Concussion incidence rates were significantly higher in female soccer players compared to male players while heading. There is also some evidence to suggest that the incidence is higher for female goalkeepers. Soccer coaches and health care providers need to recognize this sex difference when coaching or treating players. 



#14 Magnetic resonance imaging of midtarsal sprain: Prevalence and impact on the time of return to play in professional soccer players 

Reference: Eur J Radiol. 2020 Dec 24;135:109491. doi: 10.1016/j.ejrad.2020.109491. Online ahead of print. 

Authors: Miriam T Leiderer, Goetz H Welsch, Isabel Molwitz, Kai-Jonathan Maas, Gerhard Adam, Peter Bannas, Frank Oliver Henes 

Summary: Ankle sprain is a common injury in professional soccer, but to date midtarsal sprain has not been investigated in this context. The purpose of this study was to determine the prevalence of midtarsal sprain by MRI and to assess its impact on the time of return to play in professional soccer players. We included 52 professional soccer players who underwent 59 MRI examinations after acute ankle trauma between January 2012 and September 2019. Images were retrospectively reviewed in consensus by two radiologists for assessment of midtarsal sprain and ankle sprain. Ligaments were graded as i) normal, ii) partial tear, or iii) complete tear. Time to return to play (RTP) for each athlete was retrieved from team medical records. A Kruskal-Wallis test and Dunn's pairwise tests were used to calculate differences in RTP time between groups with i) isolated midtarsal sprain, ii) isolated lateral ankle sprain, and iii) combined midtarsal and lateral ankle sprain. MRI revealed isolated ankle sprain in 24 of 59 MRI examinations (40.6 %). Acute midtarsal ligament injury was present in 15 examinations (25.4 %). Four of the 15 examinations (26.7 %) had isolated midtarsal injuries and eleven of the 15 examinations (73.3 %) had concomitant ankle sprain. RTP time was 39 days (range 9-70 days) for isolated midtarsal sprain. RTP time was significantly higher for athletes with combined ankle and midtarsal sprain (47 days, range 15-74 days) when compared to athletes with isolated ankle sprain (24 days, range 2-59 days) (p = .019). Our MRI study reveals that midtarsal sprain is a frequent injury in professional soccer players with ankle sprain. Midtarsal ligament findings on MRI combined with evidence of lateral ankle sprain is associated with a longer time of return to play compared to isolated lateral ligament injuries. 



#15 Whole and peak physical characteristics of elite youth female soccer match-play 

Reference: J Sports Sci. 2020 Dec 30;1-10. doi: 10.1080/02640414.2020.1868669. Online ahead of print. 

Authors: Alice Harkness-Armstrong, Kevin Till, Naomi Datson, Stacey Emmonds

Summary: This study quantified whole and peak physical characteristics of Under (U)14 and U16 elite youth female soccer, and compared by position and age-group. Data was collected using 10 Hz GPS units from 431 match observations, during 50 matches involving 201 players (U14 n = 93; U16 n = 108) representing Regional Talent Centres in The Football Association's Girl's England Talent Pathway League. Whole match data were reported as absolute and relative; total (TD), high-speed running (HSR; ≥3.46 m·s-1), very high-speed running (VHSR; ≥5.29 m·s-1), and sprinting (SPR; ≥6.26 m·s-1) distance, and maximum velocity. Moving average analysis determined peak data (1-10 minute durations). Linear mixed models established position-specific differences. U16s covered greater; absolute distance at all speeds (small-moderate ESs; p < 0.001); relative VHSR and SPR m·min-1 (small-moderate ESs; p < 0.001); peak TD and HSR m·min-1 (small ESs) across several peak-durations, and VHSR m·min-1 (small ESs; p < 0.001) across all peak-durations compared to U14s. Position-specific differences were observed across all positions between and within both age-groups, identifying whole and peak physical characteristics are age- and position-dependent within elite youth female soccer match-play. Findings may facilitate informed coaching practices and training programme design, talent identification and development processes. 



#16 Concurrent validity, inter-unit reliability and biological variability of a low-cost pocket radar for ball velocity measurement in soccer and tennis 

Reference: J Sports Sci. 2020 Dec 30;1-8. doi: 10.1080/02640414.2020.1868090. Online ahead of print. 

Authors: Alejandro Hernández-Belmonte, Alejandro Sánchez-Pay

Summary: This study aimed to analyse the (i) concurrent validity, (ii) inter-unit reliability, and (iii) biological variability of a low-cost device called Pocket radar. Eleven men recreational soccer players performed 6 kicks to a soccer ball, whereas 13 men recreational tennis players conducted 10 shots to a tennis ball. All executions were simultaneously measured by two Pocket units and the Stalker radar (reference criterion). The within-subject variation among the executions was used for the biological variability analysis. The level of agreement and magnitude of errors included the intraclass correlation coefficient (ICC), Pearson's correlation coefficient (r), bias, and the smallest detectable change (SDC). A good agreement (ICC ≥ 0.98, r ≥ 0.98) and very low magnitude of error (SDC ≤ 7.70 km·h-1, bias ≤ 3.19 km·h-1) were found between both Pocket units and the Stalker, in soccer and tennis. Inter-unit analysis found limited technical errors (SDC ≤ 5.49 km·h-1, bias ≤ -0.93 km·h-1) and nearly perfect agreement (ICC = 0.99, r ≥ 0.98) in both sessions. These technical errors were lower than the variations due to the biological variability, in soccer (SDC = 2.47 km·h-1 vs. SDC ≥ 8.6 km·h-1) and tennis (SDC = 5.49 km·h-1 vs. SDC ≥ 21.95 km·h-1). These findings suggest the Pocket radar as a valid and highly sensitive tool for BV measurement. 






Associations Between Variations in Accumulated Workload and Physiological Variables in Young Footballers Over the Season

This study sought to analyse the relationship between in-season training workload with changes in aerobic power (VO2max), maximum and resting heart rate (HRmax and HRrest), linear sprint medium (LSM) and short test (LSS) in U16 soccer players. An additional aim was to explain changes in fitness levels during the in-season through regression models, considering accumulated load, baseline levels, and peak height velocity (PHV) as predictors.





How did three consecutive matches with extra time affect physical performance? A case study of the 2018 football Men’s World Cup

How did three consecutive matches with extra time affect physical performance? A case study of the 2018 football Men’s World Cup





Latest research in football - week 9 - 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 The Effect of Preparatory Posture on Goalkeeper's Diving Save Performance in Football 

Reference: Front Sports Act Living. 2019 Aug 21;1:15. doi: 10.3389/fspor.2019.00015. eCollection 2019. 

Authors: Rony Ibrahim, Idsart Kingma, Vosse de Boode, Gert S Faber, Jaap H van Dieën

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Summary: Identifying the optimal preparatory posture of football goalkeepers can be very relevant for improving goalkeepers' diving save performance, and coaching practices of technical and strength and conditioning coaches. This study aimed to analyse the effect of different starting stance widths and knee flexion angles on movement time, center of mass (CoM) trajectory and velocity in goalkeepers' diving saves. Ten elite goalkeepers performed dives from preferred (PT) and imposed postures, by altering knee angle (45, 75, and 90°) and stance width (50, 75, and 100% of leg length) independently, at the starting position. Repeated measures ANOVA showed a main effect of preparatory posture on dive time (p < 0.01). Pairwise comparisons showed that the fastest dive movement time was observed when goalkeepers started from a stance width of 75% (SW75). CoM traveled a larger distance between contralateral and ipsilateral peak ground reaction forces in SW75 than PT (p < 0.05). The goalkeepers were also more efficient in SW75, as a smaller countermovement and vertical velocity range were observed during high and low dives, respectively, from SW75 than PT (p < 0.05). Thus, diving from a position with wider stance width than the preferred one leads to shorter movement time, and a faster and more direct CoM trajectory toward the ball. 



#2 Role of tattoos in football: Behavioral patterns and success-analysis of the FIFA World Cup 2018

Reference: Clin Dermatol. Nov-Dec 2020;38(6):788-792. doi: 10.1016/j.clindermatol.2020.04.006.

Authors: Simon M Mueller, Michael Bayer, Mattia Antenna, Stefan Gysin

Summary: Epidemiologic studies suggest that individuals with tattoos are more extroverted, aggressive, and more likely to take risks than individuals with no tattoos. Whether these personality traits affect athletic performance is uncertain. We compared behavioral patterns and rates of success of football players at the International Federation of Association Football (FIFA) World Cup 2018 by tattoo status. In this cross-sectional study, 32.7% of football players had visible tattoos (241 of 736), mostly on their arms (97.1%). Footballers with tattoos played longer on average (208 versus 160 minutes; P < .001), received more cards (.38 versus .27; P < .001), and committed more fouls per player (2.64 versus 2.2; P < .001). Players with tattoos attempted more shots at goal (P = .016), but without higher goal success (P = .204). The higher number of disciplinary events (being whistled for fouls and given yellow or red cards) and longer playing time of football players with tattoos may reflect personality traits reported in nonathletic individuals with tattoos, such as dominance, extroversion, aggressiveness, and willingness to take risks. 



#3 Angular Velocity, Moment, and Power Analysis of the Ankle, Knee, and Hip Joints in the Goalkeeper's Diving Save in Football

Reference: Front Sports Act Living. 2020 Feb 28;2:13. doi: 10.3389/fspor.2020.00013. eCollection 2020. 

Authors: Rony Ibrahim, Idsart Kingma, Vosse de Boode, Gert S Faber, Jaap H van Dieën 

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Summary: The aim of this study was to identify biomechanical characteristics of goalkeeper's diving performance in football. Lower extremity joints powers, moments, and angular velocities, were investigated in seven elite goalkeepers diving to save balls, shot from a ball canon to unanticipated heights (high and low) and sides (right and left). Our result showed that there was a proximal-to-distal sequence for each leg in timing of peak joints powers (p < 0.05). Hip extensors produced the largest (p < 0.05) peak moment, the contralateral (relative to dive side) peak was significantly larger than the ipsilateral one for high (4.56 ± 1.02 N·m·kg-1, and 3.52 ± 0.79 N·m·kg-1) and low dives (3.52 ± 0.79 N·m·kg-1, and 2.52 ± 0.56 N·m·kg-1). The ankle plantar flexors produced the second largest peak moment (p < 0.05), and the peak ipsilateral ankle power and angular velocity were the largest (p < 0.05) of all joints, during high (1,502 ± 338 W, and 14.73 ± 1.36 rad·s-1) and low dives (868 ± 263 W, and 14.14 ± 3.09 rad·s-1). Strength and conditioning coaches need to focus on hip extensors and ankle plantar flexors, and for specificity in power training that should elicit triple extension of the lower limbs' joints in a proximal-to-distal sequence. 



#4 Referee Bias in Professional Football: Favoritism Toward Successful Teams in Potential Penalty Situations 

Reference: Front Sports Act Living. 2020 Feb 27;2:19. doi: 10.3389/fspor.2020.00019. eCollection 2020. 

Authors: Martin Kjeøen Erikstad, Bjørn Tore Johansen

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Summary: Past studies have indicated that multiple factors may influence sport referees' decisions, such as pressure from spectators and athletes' reputation. Grounded in the social impact theory framework, this study examined whether Norwegian Premier League (NPL) referees are biased by a team's success when awarding penalties. Using video footage (similar to video assistant referees), an expert panel (EP) of four NPL referees evaluated all potential penalty situations (N = 43) involving either of two successful teams during an entire NPL season. Fifty-five potential penalty situations from matches without successful teams were also rated. Overall, the match referees identified 73.3% (22 of 30) of the EP-identified penalties during matches without successful teams. Successful teams were awarded 110% (11 of 10) of the EP-identified penalties, while their opponents were awarded 12.5% (1 of 8). Chi square statistic revealed that successful teams were more likely to receive an incorrect penalty compared with their opponents, and less likely to be denied a penalty they should have been awarded. These findings indicate that referees' decisions may be unintentionally biased by a team's success, extending our knowledge about how football referees may be influenced by social forces. 



#5 Large Reductions in Match Play Physical Performance Variables Across a Professional Football Season With Control for Situational and Contextual Variables

Reference: Front Sports Act Living. 2020 Oct 15;2:570937. doi: 10.3389/fspor.2020.570937. eCollection 2020. 

Authors: Matthew Springham, Sean Williams, Mark Waldron, Darren Burgess, Robert Usher Newton

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Summary: This investigation examined match play physical performance across a professional football season using a multicamera computerized tracking system. A linear mixed-effects model, controlling for situational and contextual variables, identified decreases in team average total distance (TD): season quarter 1 (Q1) (11,047 m) > season quarter 2 (Q2) (10,473 m) (P = 0.002; ES = Small), season quarter 3 (Q3) (10,449 m) (P < 0.001; ES = Moderate), and season quarter 4 (Q4) (10,385 m) (P < 0.001; ES = Moderate); work rate (WR): Q1 (115 m/min) > Q3 (108 m/min) (P < 0.001; ES = Moderate), Q4 (107 m/min) (P < 0.001; ES = Moderate); Q2 (109 m/min) > Q4 (107 m/min) (P = 0.003; ES = Small); high-speed running distance (HSR): Q1 (1,051 m) > Q2 (813 m) (P = 0.006; ES = Small); number of high-speed runs (NHSR): Q1 (87) > Q2 (65) (P < 0.001; ES = Small), Q3 (64) (P = 0.002; ES = Small); sprint distance (SD): Q1 (202 m) > Q4 (130 m) (P < 0.001; ES = Moderate), Q2 (179 m) > Q3 (165 m) (P = 0.035; ES = Small), Q4 (130 m) (P < 0.001; ES = Moderate) and number of sprints (NS): Q1 (20.4) > Q3 (10.2) (P < 0.001; ES = Moderate), Q4 (8.3) (P < 0.001; ES = Large); Q2 (14.9) > Q3 (10.2) (P < 0.001; ES = Moderate), Q4 (8.3) (P < 0.001; ES = Large). Within-position changes were observed for WR: Q1 (122 m/min) > Q4 (113 m/min) (P = 0.002; ES = Large) in central midfielders and for NS: Q1 > Q3 in wide defenders (21.7 vs. 10.8) (P = 0.044; ES = Large) and central midfielders (18.1 vs. 8.3) (P = 0.002; ES = Large); Q1 > Q4 in central defenders (13.1 vs. 5.3) (P = 0.014; ES = Large), wide defenders (21.6 vs. 7.1) (P < 0.001; ES = Very Large), central midfielders (18.1 vs. 8.5) (P = 0.005; ES = Large), and wide midfielders (20.8 vs. 12.2) (P = 0.012; ES = Large); Q2 > Q3 in central midfielders (16.9 vs. 8.3) (P = 0.002; ES = Large) and Q2 > Q4 in wide defenders (16.3 vs. 7.1) (P = 0.005; ES = Very Large), central midfielders (16.9 vs. 8.5) (P = 0.004; ES = Large), and wide midfielders (20.8 vs. 12.2) (P = 0.007; ES = Large). The match-play physical performance was reduced across the competitive season. The most notable reductions were observed in wide defenders, central midfielders, and wide midfielders in sprint performance indices. 



#6 Origins of Relative Age Effects in Youth Football-A Nationwide Analysis 

Reference: Front Sports Act Living. 2020 Dec 3;2:591072. doi: 10.3389/fspor.2020.591072. eCollection 2020. 

Authors: Michael Romann, Eva Rüeger, Mirjam Hintermann, Raphael Kern, Oliver Faude 

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Summary: Relative age effects (RAEs) refer to the overrepresentation of players born earlier in the selection year compared to late-born players within the same age category. To date, the origins and mechanisms of RAEs are still unclear. To evaluate the development of RAEs in terms of age group and selection level, we analyzed data of all registered child and adolescent football players in Switzerland. Age category, selection level, and birthdate from all licensed 101,991 Swiss child and youth football players assigned to a specific team [9,149 girls (9.0%) and 92,842 boys (91.0%); age range: 4.6-19.6 years] were analyzed. Additionally, out of 1,128 clubs, 54 clubs provided their documented waiting lists (1,224 players). Birthdate distributions were split by age category, sex, and birth quarter (Q1 = January to March, Q4 = October to December). RAEs were calculated using odds ratios (Q1 vs. Q4) with 95% confidence intervals (95% CI). We found small RAEs among U8 players (OR 1.44 [95% CI 1.31, 1.59]) and U10 (OR 1.24 [95% CI 1.16, 1.32]). The RAE was negligible in all other age categories, independent of gender. In children's football, 5,584 (71.3%) teams performed selections. In teams without selection, there were no obvious RAEs. However, teams with selections for the same age category showed small RAEs with an overrepresentation of Q1 athletes in the first team (OR = 1.29 [95% CI 1.24, 1.35]) and inverse RAEs with an underrepresentation of Q1 athletes in the last team (OR = 0.85 [95% CI 0.82, 0.89]). Only small RAEs were observed on the waiting lists for the U8 (OR = 1.48 [1.13, 1.95]). RAEs have a small, but consistent effect on participation in Swiss children's football at the grassroots level. Contrary to expectations, no inverse RAEs were found on the waiting lists. Nonetheless, first time coach selections seem to be the origin of RAEs. To protect young athletes from discrimination, RAE biases should be analyzed and eliminated at all stages of sport participation, selection, and dropout situations. Modifications to the organizational structure of sport and athlete development systems are recommended to prevent RAE-related discrimination in youth sports. 



#7 Asymptomatic Degenerative Changes in the Lumbar Spine Among Professional Soccer Players 

Reference: Spine (Phila Pa 1976). 2021 Jan 15;46(2):122-128. doi: 10.1097/BRS.0000000000003726. 

Authors: Eduard Bezuglov, Artemii Lazarev, Arseniy Petrov, Alesia Brodskaia, Anastasiya Lyubushkina, Kamila Kubacheva, Evgeny Achkasov, Vladimir Nikolenko

Summary: The aim of this study was to evaluate the actual prevalence of degenerative spinal changes and their association with age in a cohort of professional soccer players. Presently, there are data that athletes have more degenerative changes than nonathletes; however, the research examining the prevalence of degenerative spinal conditions among professional elite soccer players is scarce. Professional male soccer players were included in the study (n = 40, average age 26,6 ± 4,5 years, average height 18 ± 0.07 m, weight 76.7 ± 7.1 kg). Lumbosacral spine MRI scanning at the L1-S1 level has been performed. Two radiologists with at least 7 years of experience of working with athletes evaluated all images independently of each other. 92.5% (n = 37) of soccer players had ≥1 spinal degenerative condition. Thirty-five percent (n = 14) of players had three to five, and 50% (n = 20) had six or more conditions. The average age of players who had six or more conditions was significantly higher than those who had zero to five or three to five conditions-28.1 ± 4.8 years versus 25.1 ± 3.6 years (P = 0.029), and 24.8 ± 3.6 years, respectively.Kruskal-Wallis test has shown no association between the number of degenerative conditions and weight (P = 0.98) as well as body mass index (P = 0.99). The age was associated with degenerative changes (P = 0.008).Disc desiccation was the most common pathologic condition, which was found in 82.5% of athletes. Facet joint arthropathy and spondylosis were present in 70, and 50% of the studied lumbar spine MRI scans, respectively. The spondylolysis prevalence of 20% was noted. Elite professional soccer players demonstrate a high prevalence of asymptomatic degenerative lumbar spinal degenerative changes, which are significantly associated with age. These conditions might lead to the development of symptomatic lower back pain, given the high-intensity exercise required in professional soccer. It is presently unclear what measures might be applied for the primary prevention of these degenerative spinal conditions.Level of Evidence: 4. 



#8 Covid-19 Has Turned Home Advantage Into Home Disadvantage in the German Soccer Bundesliga 

Reference: Front Sports Act Living. 2020 Nov 5;2:593499. doi: 10.3389/fspor.2020.593499. eCollection 2020. 

Authors: Markus Tilp, Sigrid Thaller

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Summary: The main factors for home advantage (HA), quantified by the number of points won at home expressed as a percentage of all points, are believed to be crowd support, territoriality, familiarity, and travel fatigue. In 2020, the German Soccer Bundesliga interrupted its championship due to the Covid-19 pandemic after 25 rounds and the last nine rounds were played without audience. This unique situation allowed studying the effect of spectators on the team's performance and the referee's decisions. We hypothesized a decrease in HA and a more balanced distribution of fouls and disciplinary cards in the games without audience (GWOA) compared to the games with audience (GWA). We evaluated n = 223 GWA and n = 83 GWOA of the season 2019/20 and all games of the preceding season 2018/19 to analyze the distribution of game outcomes (wins, losses, and draws) and HA. We analyzed the number of fouls, disciplinary cards, and penalty kicks. We found significant differences in HA between GWA (HA = 54.35%) and GWOA (HA = 44.1%) as well as GWOA and games of 2018/19 (HA = 57.63%). The distribution of game outcomes in GWOA did not differ from GWA but differed significantly from 2018/19 (p = 0.031). The distribution of fouls showed a significant difference to equal distribution in GWA [home: 2,595 (48.56%); away: 2,749 (51.44%)] but not in GWOA [home: 1,067 (50.54%); away: 1,044 (49.46%)]. In the GWOA, we counted 178 (51.1%, home) and 170 (48.9%, away) cards, representing a significant difference in the distribution to GWA [home: 405 (44.85%); away: 498 (55.15%)]. The number of red cards differed significantly from an equal distribution for GWA (14 home and 28 away) but not for GWOA (eight home and seven away). In the last nine rounds without audience, we observed more home losses (36) than home wins (27). Hence, the Covid-19 lock-down led to a home disadvantage. One reason for this surprising result could be that the home team is missing an important familiar aspect when playing in their empty stadium without social support from their home audience. Furthermore, both teams know about the HA thus the away team could be more motivated in this unusual situation. 



#9 Effect of Practicing Soccer Juggling With Different Sized Balls Upon Performance, Retention, and Transfer to Ball Reception 

Reference: Motor Control. 2016 Oct;20(4):337-49. doi: 10.1123/mc.2015-0026. Epub 2016 Aug 19. 

Authors: Olav Raastad, Tore Kristian Aune, Roland van den Tillaar

Summary: The aim of this study was to investigate if making the skill acquisition phase more difficult or easier would enhance performance in soccer juggling, and if this practice has a positive intertask transfer effect to ball reception performance. Twenty-two adolescent soccer players were tested in juggling a soccer ball and in the control of an approaching ball at a pre, post and retention test. The participants were randomly divided in a small ball size and bigger ball size training group that both trained four times per week for 6 weeks. At the post and retention test both groups enhanced performance in soccer juggling test with no difference between groups and no increase in ball reception performance at these tests. It was concluded that about intra task transfer and retention of soccer juggling skills, it does not matter if you increase (small balls) or decrease the difficulty (larger balls) when using the same amount of practice time within the skill acquisition phase in soccer juggling. In addition that for ball juggling and ball reception (inter task) these two tasks differ too much in afferent information and movement characteristics that no positive transfer between these two skills no positive intertask transfer can be expected. 



#10 Acute effects of small-sided games combined with running drills on internal and external loads in young soccer players 

Reference: Biol Sport. 2020 Dec;37(4):375-381. doi: 10.5114/biolsport.2020.96943. Epub 2020 Jul 5. 

Authors: Yusuf Köklü, Hamit Cihan, Utku Alemdaroğlu, Alexandre Dellal, Del P Wong

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Summary: The purpose of this study was to compare the effects of regular small-sided games (SSGreg) and SSGs combined with running drills (SSGcom) on players' internal and external loads. Eighteen young male soccer players (average age: 18.2 ± 0.5 years) participated in 3 vs. 3 and 4 vs. 4 games, under both SSGreg and SSGcom conditions. SSGreg bouts were played for 4 minutes without additional running drills, while SSGcom bouts consisted of 3 min 30 s SSG and 15 s running before and after the bout, making the duration of each bout 4 minutes. During all SSGs, measurements of heart rate (HR) responses as well as distances covered in four different speed zones - walking (WLK), low-intensity (LIR), moderate-intensity (MIR) and high-intensity running (HIR) - were recorded. Technical characteristics were monitored during the SSGs, and the rating of perceived exertion (RPE) and blood lactate (La-) responses were determined at the end of each SSG condition. Compared to the SSGreg in both 3 vs. 3 and 4 vs. 4 formats, the SSGcom condition resulted in higher La- and RPE responses (p < 0.05), greater distance covered at MIR and HIR speeds and greater total distance (p < 0.05). The results of this study show that replacing 30 s within the 4-min bouts of SSGs (both 3- and 4-a-side) by 2 x 15 s of running drills is effective in increasing internal (La- and RPE) and external loads (MIR and HIR) without a significant decrease in total passes and successful passes in young soccer players. 



#11 Are There Differences in Concentric Isokinetic Strength Performance Profiles between International and Non-International Elite Soccer Players? 

Reference: Int J Environ Res Public Health. 2020 Dec 23;18(1):E35. 

doi: 10.3390/ijerph18010035. 

Authors: Robert Śliwowski, Jakub Marynowicz, Monika Grygorowicz, Andrzej Wieczorek, Łukasz Jadczak

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Summary: The purpose of this study is to evaluate the differences in concentric isokinetic strength characteristics of the knee extensor and knee flexor musculature between international (IL) and non-international level (N-IL) soccer players. The second aim is to establish strength symmetry status in knee muscles for dominant (DL) and non-dominant (NDL) legs for both within and between groups. 100 male top elite soccer players (IL: n = 36, age = 27.5 ± 3.4 years and N-IL: n = 64, age = 27.7 ± 6.4 years) underwent concentric isokinetic strength tests, using a Biodex System 3 dynamometer. Results indicate that statistically significant differences between groups were noted for peak torque of hamstrings (PT-H), hamstrings/quadriceps (H/Q) ratio, and total work of hamstrings (TW-H), where mean values for the IL were similarly higher than for the N-IL group (p = 0.006, p < 0.001, and p = 0.012, respectively). Our results also showed statistically significant differences for peak torque of quadriceps (PT-Q), PT-H, total work of quadriceps (TW-Q) and TW-H between legs, where mean values noted for the DL were higher than for the NDL for both groups (p = 0.021, p < 0.001, p = 0.006, and p = 0.004, respectively). Additional results show that IL players presented more symmetrical strength between legs than N-IL. The results of this study indicate that that the greatest differences in isokinetic strength performance across players at different soccer levels relate to the hamstring muscle. As a result, systematic strength training of these muscle groups is strongly recommended. 



#12 Internal (Factorial) Validity of the ANAM using a Cohort of Woman High-School Soccer Players 

Reference: Arch Clin Neuropsychol. 2020 Dec 29;acaa120. doi: 10.1093/arclin/acaa120. Online ahead of print. 

Authors: Joseph J Glutting, Adam Davey, Victoria E Wahlquist, Marley Watkins, Thomas W Kaminski

Summary: Computerized neuropsychological testing is a cornerstone of sport-related concussion assessment. Female soccer players are at an increased risk for concussion as well as exposures to repetitive head impacts from heading a soccer ball. Our primary aim was to examine factorial validity of the Automated Neuropsychological Assessment Metrics (ANAM) neuropsychological test battery in computing the multiple neurocognitive constructs it purports to measure in a large cohort of interscholastic female soccer players. Study participants included 218 interscholastic female soccer players (age = 17.0±0.7 year; mass = 55.5±6.8 kg; height = 164.7±6.6 cm) drawn from a large (850+) prospective database examining purposeful heading from four area high schools over a 10-year period. The ANAM-2001 measured neurocognitive performance. Three methods were used to identify integral constructs underlying the ANAM: (a) exploratory factor analysis (EFA), (b) first-order confirmatory factor analysis (CFA), and (c) hierarchical CFA. Neuropsychological phenomena measured by the ANAM-2001 were best reproduced by a hierarchical CFA organization, composed of two lower level factors (Simple Reaction Time, Mental Efficiency) and a single, general composite. Although the ANAM was multidimensional, only the composite was found to possess sufficient construct dimensionality and reliability for clinical score interpretation. Findings failed to uphold suppositions that the ANAM measures seven distinct constructs, or that any of its seven tests provide unique information independent of other constructs, or the composite, to support individual interpretation. Outcomes infer the ANAM possesses factorial-validity evidence, but only scores from the composite appear to sufficiently internally valid, and reliable, to support applied use by practitioners. 



#13 SOS to the Soccer World. Each Time the Preseason Games Are Less Friendly 

Reference: Front Sports Act Living. 2020 Dec 18;2:559539. doi: 10.3389/fspor.2020.559539. eCollection 2020. 

Authors: Julio Calleja-Gonzalez, Carlos Lalín, Francesc Cos, Diego Marques-Jimenez, Pedro E Alcaraz, Antonio José Gómez-Díaz, Tomás T Freitas, Juan Mielgo Ayuso, Irineu Loturco, Xavi Peirau, Ignacio Refoyo, Nicolas Terrados, Jaime E Sampaio 

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#14 Changes in sprint performance and sagittal plane kinematics after heavy resisted sprint training in professional soccer players

Reference: PeerJ. 2020 Dec 15;8:e10507. doi: 10.7717/peerj.10507. eCollection 2020. 

Authors: Johan Lahti, Toni Huuhka, Valentin Romero, Ian Bezodis, Jean-Benoit Morin, Keijo Häkkinen 

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Summary: Sprint performance is an essential skill to target within soccer, which can be likely achieved with a variety of methods, including different on-field training options. One such method could be heavy resisted sprint training. However, the effects of such overload on sprint performance and the related kinetic changes are unknown in a professional setting. Another unknown factor is whether violating kinematic specificity via heavy resistance will lead to changes in unloaded sprinting kinematics. We investigated whether heavy resisted sled training (HS) affects sprint performance, kinetics, sagittal plane kinematics, and spatiotemporal parameters in professional male soccer players. After familiarization, a nine-week training protocol and a two-week taper was completed with sprint performance and force-velocity (FV) profiles compared before and after. Out of the two recruited homogenous soccer teams (N = 32, age: 24.1 ± 5.1 years: height: 180 ± 10 cm; body-mass: 76.7 ± 7.7 kg, 30-m split-time: 4.63 ± 0.13 s), one was used as a control group continuing training as normal with no systematic acceleration training (CON, N = 13), while the intervention team was matched into two HS subgroups based on their sprint performance. Subgroup one trained with a resistance that induced a 60% velocity decrement from maximal velocity (N = 10, HS60%) and subgroup two used a 50% velocity decrement resistance (N = 9, HS50%) based on individual load-velocity profiles. Both heavy resistance subgroups improved significantly all 10-30-m split times (p < 0.05, d = - 1.25; -0.62). Post-hoc analysis showed that HS50% improved significantly more compared to CON in 0-10-m split-time (d = 1.03) and peak power (d = 1.16). Initial maximal theoretical horizontal force capacity (F0) and sprint FV-sprint profile properties showed a significant moderate relationship with F0 adaptation potential (p < 0.05). No significant differences in sprinting kinematics or spatiotemporal variables were observed that remained under the between-session minimal detectable change. With appropriate coaching, heavy resisted sprint training could be one pragmatic option to assist improvements in sprint performance without adverse changes in sprinting kinematics in professional soccer players. Assessing each player's initial individual sprint FV-profile may assist in predicting adaptation potential. More studies are needed that compare heavy resisted sprinting in randomized conditions. 



#15 Reliability assessment of the functional movement screen for predicting injury risk in Japanese college soccer players 

Reference: J Phys Ther Sci. 2020 Dec;32(12):850-855. doi: 10.1589/jpts.32.850. Epub 2020 Dec 11. 

Authors: Takayuki Miyamori, Masashi Nagao, Yu Shimasaki, Takayuki Okazaki, Naoki Akiyoshi, Hirofumi Nishio, Yuji Takazawa, Masafumi Yoshimura

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Summary: This study aimed to assess the reliability of the Functional Movement Screen and explore whether this evaluation tool can predict the risks of personal injuries in Japanese soccer players. Seventy-five Japanese college soccer players who participated in our 1 year prospective cohort study underwent a Functional Movement Screen assessment. Demographic data, athletic characteristics, and types and frequency of injuries sustained, were analyzed with the assessment results. There was no significant difference in the mean Functional Movement Screen composite scores between genders. Although the Functional Movement Screen showed excellent inter-rater reliability (0.92), low overall internal consistency (0.35) was observed. A maximum score of 3 in straight leg raise occurred in 94% of the females and was considered a ceiling effect. None of the cut-off point scores of the Functional Movement Screen were associated with the number of overall injuries, lower limb injuries, and traumatic injuries, or time to return to play. The Functional Movement Screen composite score of ≤15 represented the maximum sensitivity of 76.92% and specificity of 34.78% with 0.56 in the area under the curve. Functional Movement Screen composite scores do not have sufficient sensitivity and specificity for predicting injuries in Japanese college soccer players. 






Optimal Pretaper Phase on Physical Match Performance in Professional Soccer

The aim was to investigate the optimal pretaper duration on match running performance in a professional soccer team.






Eyes-Open Versus Eyes-Closed Somatosensory Motor Balance in Professional Soccer Players With Chronic Ankle Instability

The aim was to compare an eyes-open versus an eyes-closed balance training protocol in professional soccer players with chronic ankle instability





Latest research in football - week 8 - 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 Lack of Abdominal Stability and Control as a Possible Contributor to Rectus Femoris Avulsion Fracture in the Adolescent Soccer Player: A Case Report 

Reference: Pediatr Phys Ther. 2021 Jan 1;33(1):E15-E22. doi: 10.1097/PEP.0000000000000773. 

Authors: Chelsea Lasky-McFarlin, Mae Thomas, Jennifer Newman, Deborah Thorpe 

Summary: The purpose was to describe evaluation and physical therapy treatment for an athlete who is male and 13 years old with healing bilateral rectus femoris avulsion fractures. Fractures of the anterior inferior iliac spine may be linked to poor abdominal stability in soccer athletes who are male and an adolescent. The development and use of an abdominal stability screening tool could be an efficient and effective way to determine fracture risk and guide prevention programs. Following 8 weeks of conservative physical therapy treatment, the athlete met all goals and returned to pain-free soccer activities without residual impairments. Four months following discharge, he reported full participation in soccer competition without complications. This case illustrates that abdominal weakness is a potential risk factor for anterior inferior iliac spine avulsion fracture. Screening for abdominal weakness and incorporating preventative programs into training regimens is recommended to prevent anterior inferior iliac spine injuries in this population. 



#2 Urinary N-Terminal Fragment of Titin Reflects Muscle Damage After a Soccer Match in Male Collegiate Soccer Players 

Reference: J Strength Cond Res. 2020 Dec 17;Publish Ahead of Print. doi: 10.1519/JSC.0000000000003923.

Authors: Yoko Tanabe, Kazuhiro Shimizu, Emi Kondo, Mikinobu Yasumatsu, Daisuke Nakamura, Hiroyuki Sagayama, Hideyuki Takahashi 

Summary: Previous studies have demonstrated that noninvasive urinary N-terminal fragment of titin (U-titin) concentration highly correlates with serum creatine kinase (CK) activity, a classic invasive muscle damage marker. This finding indicates that U-titin could be used to estimate muscle damage. However, these results were achieved using a laboratory-based eccentric exercise model. Therefore, it remains unclear whether U-titin is useful for evaluating muscle damage occurring in field sports events. As a result, we evaluated whether U-titin concentration closely relates to serum CK activity after a soccer match. Seventeen collegiate soccer players (age: 20 ± 1 year; height: 172 ± 6 cm; body mass: 65 ± 5 kg; Yo-Yo intermittent recovery test level 2, 1,135 ± 196 m) completed a test match (2 halves of 45 minutes separated by 15 minutes of normal half-time). U-titin concentration, serum CK activity, countermovement jump performance, and muscle soreness were assessed 2 hours before the match and 30 minutes, 24 hours, and 48 hours after the match. U-titin concentrations and CK activity similarly increased at 24 hours and returned to the baseline value at 48 hours after the match. Moreover, the percentage of changes in U-titin concentration from baseline after the match significantly and positively correlated with serum CK activity (r = 0.82, p < 0.05). These results suggest that the noninvasive marker U-titin can be used to assess muscle damage conditions in field sports events, such as soccer matches. 



#3 Elite Soccer Players do Not Cover Less Distance in the Second Half of the Matches When Game Interruptions Are Considered 

Reference: J Strength Cond Res. 2020 Dec 17;Publish Ahead of Print. doi: 10.1519/JSC.0000000000003935.

Authors: Ezequiel Rey, Anton Kalén, Miguel Lorenzo-Martínez, Roberto López-Del Campo, Fabio Nevado-Garrosa, Carlos Lago-Peñas 

Summary: This study aimed to analyze quantitative differences in the physical demands of male elite soccer players between the first and second halves during official matches, accounting for effective playing time (the duration of play after subtracting the game interruptions) and playing positions. A total of 4,249 individual match observations of 412 outfield players competing in the Spanish first division league (LaLiga) were undertaken during the 2018-2019 season, using a computerized tracking system (TRACAB, Chyronhego, New York, NY). The players were classified into 5 positional roles: central defenders (CD), external defenders (ED), central midfielders (CM), external midfielders (EM), and forwards (F). The main results showed that in contrast to those observed when total playing time was considered, independent of playing position, there were no significant differences on high-speed running (HSR) (5.5 ± 2.4 vs. 5.5 ± 2.4 m·min-1) and sprint (5.3 ± 3.3 vs. 5.4 ± 3.3 m·min-1) distances between the first and second halves in professional soccer players when the effective playing time was considered. However, differences in match running performance at HSR and sprint distances between the first and second halves were dependent on players' playing position. Whereas ED and EM maintained HSR and sprint efforts during the second half, CD and CM significantly increased (p < 0.001) the distance covered at sprint during the second period of the match. Contrarily, F were unable to maintain their HSR (6.2 ± 2.3 vs. 5.9 ± 3.3 m·min-1) and sprint (7.0 ± 3.5 vs. 6.5 ± 3.4 m·min-1) match running performances during the second half. Such findings demonstrate that total playing time could overestimate fatigue-induced performance declines. Thus, effective playing time and playing position should be taken into account when interpreting the match running performance of professional soccer players. 



#4 Sprint and jump performances in highly trained young soccer players of different chronological age: Effects of linear vs. change-of-direction sprint training 

Reference: J Exerc Sci Fit . 2021 Apr;19(2):81-90. doi: 10.1016/j.jesf.2020.10.003. Epub 2020 Nov 13. 

Authors: Thomas Pavillon, Claire Tourny, Abderraouf Ben Aabderrahman, Iyed Salhi, Sghaeir Zouita, Mehdi Rouissi, Anthony C Hackney, Urs Granacher, Hassane Zouhal

Summary: The aim of this study was to examine the effects of two different sprint-training regimes on sprint and jump performances according to age in elite young male soccer players over the course of one soccer season. Players were randomly assigned to two training groups. Group 1 performed systematic change-of-direction sprints (CODST, U19 [n = 9], U17 [n = 9], U15 [n = 10]) while group 2 conducted systematic linear sprints (LST, U19 [n = 9], U17 [n = 9], U15 [n = 9]). Training volumes were similar between groups (40 sprints per week x 30 weeks = 1200 sprints per season). Pre and post training, all players performed tests for the assessment of linear and slalom sprint speed (5-m and 10-m), countermovement jump, and maximal aerobic speed performance. For all physical fitness measures, the baseline-adjusted means data (ANCOVA) across the age groups showed no significant differences between LST and CODST at post (0.061 < p < 0.995; 0.0017 < d < 1.01). The analyses of baseline-adjusted means for all physical fitness measures for U15, U17, and U19 (LST vs. CODST) revealed no significant differences between LST and CODST for U15 (0.213 < p < 0.917; 0.001 < d < 0.087), U17 (0.132 < p < 0.976; 0.001 < d < 0.310), and U19 (0.300 < p < 0.999; 0.001 < d < 0.049) at post. The results from this study showed that both, LST and CODST induced significant changes in the sprint, lower limbs power, and aerobic performances in young elite soccer players. Since no significant differences were observed between LST and CODST, the observed changes are most likely due to training and/or maturation. Therefore, more research is needed to elucidate whether CODST, LST or a combination of both is beneficial for youth soccer athletes' performance development. 



#5 Biological Maturity Status in Elite Youth Soccer Players: A Comparison of Pragmatic Diagnostics With Magnetic Resonance Imaging 

Reference: Front Sports Act Living. 2020 Dec 15;2:587861. doi: 10.3389/fspor.2020.587861. eCollection 2020. 

Authors: Daniel Leyhr, Dennis Murr, Lajos Basten, Katrin Eichler, Thomas Hauser, Dennis Lüdin, Michael Romann, Giuseppe Sardo, Oliver Höner

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Summary: The influence of biological maturity status (BMS) on talent identification and development within elite youth soccer is critically debated. During adolescence, maturity-related performance differences within the same age group may cause greater chances of being selected for early maturing players. Therefore, coaches need to consider players' BMS. While standard methods for assessing BMS in adolescents are expensive and time-consuming imaging techniques (i.e., X-ray and MRI), there also exist more pragmatic procedures. This study aimed to evaluate commonly used methods to assess BMS within a highly selected sample of youth soccer players. A total of N = 63 elite male soccer players (U12 and U14) within the German Soccer Association's talent promotion program completed a test battery assessing BMS outcomes. Utilizing MRI diagnostics, players' skeletal age (SAMRI) was determined by radiologists and served as the reference method. Further commonly used methods included skeletal age measured by an ultrasound device (SAUS), the maturity offset (MOMIR), and the percentage of adult height (PAHKR). The relation of these alternative BMS outcomes to SAMRI was examined using different perspectives: performing bivariate correlation analyses (1), modeling BMS as a latent variable (BMSlat) based on the multiple alternative diagnostics (2), and investigating individual differences in agreement (3). (1) Correlations of SAMRI and the further BMS variables ranked from r = 0.80 to r = 0.84 for the total sample and were lower for U12 (0.56 ≤ r ≤ 0.66), and U14 (0.61 ≤ r ≤ 0.74) (2). The latent structural equation modeling (SEM) (R 2 = 51%) revealed a significant influence on BMSlat for MOMIR (? = 0.51, p <0.05). The additional contribution of PAHKR (? = 0.27, p = 0.06) and SAUS (? = -0.03, p = 0.90) was rather small (3). The investigation of individual differences between the reference method and alternative diagnostics indicated a significant bias for MOMIR (p <0.01). The results support the use of economical and time-efficient methods for assessing BMS within elite youth soccer. Bivariate correlation analyses as well as the multivariate latent variable approach highlight the measures' usefulness. However, the observed individual level differences for some of the utilized procedures led to the recommendation for practitioners to use at least two alternative assessment methods in order to receive more reliable information about players' BMS within the talent promotion process. 



#6 Longitudinal Physical Development of Future Professional Male Soccer Players: Implications for Talent Identification and Development? 

Reference: Front Sports Act Living . 2020 Oct 21;2:578203. doi: 10.3389/fspor.2020.578203. eCollection 2020. 

Authors: Chris Saward, Mark Hulse, John G Morris, Heita Goto, Caroline Sunderland, Mary E Nevill

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Summary: The present study examined if elite youth male association football (soccer) players aged 8-19 y (n = 2,875) from the English talent development system, who ultimately achieved professional status differed in stature, body mass, and physical performance (20-m sprint speed, slalom agility speed, vertical counter-movement jump with arm swing jump height, multistage fitness test distance) compared with their non-professional peers. The study also examined the longitudinal pattern of development of stature, body mass, and physical performance, and if this was different between future professionals and non-professionals, while considering the effects of playing position. Multilevel modeling of the 8,898 individual (player-occasion) data points suggested that from age 12.0, the future professionals performed better in a vertical counter-movement jump with arm swing test and slalom agility test than future non-professionals, and improved at a faster rate, so that by age 18.0 the differences in vertical counter-movement jump with arm swing and slalom agility performance were 1.7 cm (p < 0.001, d = 0.3) and 0.14 s (p < 0.001, d = 0.5), respectively. In addition, future professionals were faster (by 0.02-0.04 s on the 20-m sprint, p < 0.001, d = 0.2) and ran further in the multistage fitness test (by 47 m, p = 0.014, d = 0.2) than future non-professionals throughout their development, but there were no differences in stature or body mass during development between the groups. Whereas, multistage fitness test performance improved linearly with age, the development of all other physical characteristics was non-linear. There were inter-individual differences in the development of all characteristics, and there were differences between playing positions in the development of all characteristics. Thus, in summary, future professionals jump higher, are more agile, faster, and more endurance fit than future non-professionals as they age, and the pattern of development is different in professionals and non-professionals for vertical jumping and slalom agility performance. 



#7 Female Youth Soccer Participation and Continued Engagement: Associations With Community Size, Community Density, and Relative Age 

Reference: Front Sports Act Living. 2020 Sep 18;2:552597. doi: 10.3389/fspor.2020.552597. eCollection 2020. 

Authors: Kristy L Smith, Patricia L Weir 

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Summary: Environmental context can impact youth engagement in sport and athlete development. Previous work has examined the population size of the birthplace of elite athletes; commonly known as the birthplace or community size effect. Community density has also been recognized as an important variable. Exact estimates for the ideal community characteristics and a thorough understanding of the underlying mechanisms has been somewhat elusive. Existing studies are cross-sectional in nature and there is evidence to suggest that significant variation exists within imposed categories. An athlete's birthdate position in a similar-age cohort can also impact development and has been associated with (dis)advantages resulting from subtle age differences (i.e., the relative age effect); it remains unknown if this variable is associated with population density. The objective of this study was to establish longitudinal participation trends among female youth soccer players in Ontario Canada, with consideration of community size, community density, and relative age. Within-category variation and associations between the variables were assessed. Registration entries at age 10 years (n = 9,826) and 16 years (n = 2,305) were isolated for analysis. Odds ratio analyses were conducted within each community size and density category for all 10 year old registrants; 95% confidence intervals were obtained. This procedure was repeated for all registrants at 16 years of age using the expected distribution at age 10 years to examine continued engagement. Findings suggest medium-sized communities (i.e., 10,000-249,999 inhabitants) provide the best odds of participation and continued engagement. Less densely populated communities (i.e., 50-<400 population/km2) appeared to be ideal for facilitating participation at age 10 years, but not for engagement at age 16 years. However, within-category variation was evident when each community was inspected individually. Consistent with previous attempts to find an association between community size and the relative age effect, there did not appear to be an association between community density and birth quartile distribution. Observations from this study show that community size and community density are truly unique and separate variables. Future studies should consider the underlying contributions to both low and high participation and continued engagement, while being mindful of within-category variation. 



#8 Endurance Capacities in Professional Soccer Players: Are Performance Profiles Position Specific? 

Reference: Front Sports Act Living. 2020 Sep 18;2:549897. doi: 10.3389/fspor.2020.549897. eCollection 2020. 

Authors: Stefan Altmann, Rainer Neumann, Alexander Woll , Sascha Härtel

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Summary: The aim of this study was to investigate position-specific endurance performance of soccer players. 136 professional players competing in the 1st and 2nd division in Germany were divided into the positional groups goalkeepers (GK), central defenders (CD), wingers (WI), central midfielders (CM), and forwards (FW). All players performed an incremental treadmill test with blood lactate sampling until exhaustion with the following endurance parameters being obtained: Fixed aerobic threshold (v2mmol/l), fixed anaerobic threshold (v4mmol/l), individual aerobic threshold (vLT), individual anaerobic threshold (vIAT), and maximum velocity (vmax). Results revealed significant differences between GK and all outfield playing positions for all endurance parameters (p ≤ 0.03; ES 0.87-2.19). No significant differences among outfield playing positions were evident for any of the parameters. However, trends were found in favor of the CM compared to the WI (p = 0.11; ES = 0.68) and the FW (p = 0.06; ES = 0.47) relating to vLT as well as in favor of the CM compared to the WI (p = 0.10; ES = 0.56) relating to vIAT. Findings suggest that goalkeepers possess the lowest endurance capacity compared to other playing positions. While outfield players in general showed similar endurance performance, CM seem to possess the highest aerobic capacity of all positions as indicated by all lactate-based thresholds, however, with only small to moderate ES. These findings could lead one to question the appropriateness of current endurance training regimes to prepare all players adequately for their positional match-running demands. Indeed, endurance training of players should be specific to their match-running demands. However, it remains unknown to what extent these demands are position or player specific. 



#9 Player Monitoring in Professional Soccer: Spikes in Acute:Chronic Workload Are Dissociated From Injury Occurrence 

Reference: Front Sports Act Living. 2020 Jul 8;2:75. doi: 10.3389/fspor.2020.00075. eCollection 2020. 

Authors: Luis Suarez-Arrones, Borja De Alba, Mareike Röll, Ignacio Torreno, Sarah Strütt, Kathrin Freyler, Ramona Ritzmann

Summary: This study aimed to determine whether spikes in acute:chronic workload ratio (ACWR) are associated with injury incidence, and to examine the differences in external load due to greater or lesser exposure to matches and the long-term effects of the load during a chronic seasonal period. Fifteen professional soccer players belonging to the squad of a European Champions League club were enrolled in this study. External training and match load were assessed from all athletes using a global positioning system (GPS). We calculated the uncoupled ACWR for 10 consecutive competitive microcycles. Injuries were identified and determined by the days of absence. The differences in external load were determined using a linear mixed-model approach. In addition to the null hypothesis testing, the effect size was calculated. Thirteen athletes who did not suffer an injury exceeded several times the critical threshold of an ACWR > 1.5. This is equivalent to 1 player exceeding the critical threshold for ACWR in total distance (TD), 2 players for ACWR at distance covered above moderate speed (MSD), 2 players for ACWR at distance covered above high speed (HSD), 2 players for ACWR at distance covered above very high speed (VHSD), and 2 players for ACWR in DC at sprint per week. One athlete experienced a non-contact muscle strain injury and another a contact -injury manifested as a concussion; both athletes document an ACWR <1.5 within the 4 weeks prior to the injury event. Players with lesser participation in official games covered lower TD (-19.6%, very-large ES), MSD (-24.8%, very-large ES), HSD (-25.1%, moderate ES), VHSD (-25.5%, moderate ES), and DC at sprint (-30.6%, moderate ES) over the course of the 10-weeks period in comparison with the players with greater participation in official games. The present study demonstrated that spikes in the ACWR were not related to a subsequent injury occurrence in professional soccer players. Differences in participation in official games caused significant imbalances in the chronic external loads between players in a squad, which should be minimized in training sessions in order to prevent substantial changes in workload for those who usually do not play. 



#10 Biomarkers Correlate With Body Composition and Performance Changes Throughout the Season in Women's Division I Collegiate Soccer Players 

Reference: Front Sports Act Living. 2020 Jul 2;2:74. doi: 10.3389/fspor.2020.00074. eCollection 2020. 

Authors: Bridget A McFadden, Alan J Walker, Michelle A Arent, Brittany N Bozzini, David J Sanders, Harry P Cintineo, Marissa L Bello, Shawn M Arent

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Summary: The purpose of this study was to evaluate the effects of a competitive soccer season on biomarkers and performance metrics in order to determine the correlation between changes in biomarkers, body composition, and performance outcomes. Twenty-one Division 1 female collegiate soccer players were monitored throughout the 16-week season. Player workload was measured using heart rate and Global Position Satellite systems at all practices and games. Performance testing, including vertical jump, VO2max, and 3-repetition maximum testing for bench press, squat and deadlift, occurred prior to pre-season and immediately post-season. Blood draws occurred prior to preseason and every 4-weeks thereafter, following a game. Body composition was assessed prior to the start of season (week 0) and weeks 6, 10, 14, and 17 (post-season). Delta area under the curve was calculated for biomarkers and body composition variables to account for seasonal changes adjusted for baseline. Pearson-product moment correlations were used to assess relationships with significance set at p < 0.05. Trends were considered p ≤ 0.10. No significant time main effects were seen for anabolic biomarkers (p > 0.05). Significant time effects were seen for catabolic biomarkers throughout the season (p = 0.001). No changes in body weight, VO2max, vertical jump, and deadlift occurred. Squat and bench press improved (p = 0.01 and p = 0.02, respectively) with a decline in percent body fat (p = 0.03) and a trend for increased fat free mass (p = 0.09). Additionally, total cortisol (TCORT) negatively correlated with fat free mass (r = -0.48; p = 0.03) and positively correlated with VO2max (r = 0.47; p = 0.04). A trend was shown for a positive correlation between both TCORT and free cortisol (FCORT) and percent body fat (r = 0.39; r = 0.40; p = 0.08, respectively). IGF-1 and growth hormone positively correlated to deadlift (r = 0.57; P = 0.02 and r = 0.59; p = 0.03), whereas creatine kinase showed a trend for a positive correlation with deadlift (r = 0.49; p = 0.06). IL-6 negatively correlated with bench press (r = -0.53; p = 0.03). These findings support a relationship between biomarkers, performance outcomes, and body composition. Biomarker monitoring may be useful to detect individual player's physiological response to an athletic season and may help provide insights in efforts to optimize performance outcomes. 



#11 The Effects of Cold Water Immersion on the Recovery of Drop Jump Performance and Mechanics: A Pilot Study in Under-20 Soccer Players 

Reference: Front Sports Act Living. 2020 Mar 31;2:17. doi: 10.3389/fspor.2020.00017. eCollection 2020. 

Authors: Adam Kositsky, Janne Avela

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Summary: Cold water immersion (CWI) is a popular method used for enhancing recovery from exercise. However, the efficacy of this approach is inconclusive and studies investigating variables contributing to overall performance are scarce. Additionally, few studies have investigated the recovery of stretch-shortening cycle (SSC) performance after a fatiguing SSC task. The SSC occurs naturally in human locomotion and induces a recovery pattern different from isolated muscle contractions (e.g., pure eccentric exercise). Therefore, the main aim of this study was to investigate the effects of a single CWI on jumping performance and mechanics after exhaustive SSC exercise. On a sledge apparatus, 10 male under-20 soccer players (age 18-20 years) performed five sets of 20 maximal drop jumps (DJ) followed by continuous submaximal rebounding. Subjects were equally randomized into a passive recovery control (CON) or CWI group (10 ± 0.5°C for 20 min). Prior to, upon completion of, and at 24 and 48 h follow-ups, subjects performed maximal DJs recorded with a high-speed video camera. Blood samples were taken and subjective muscle soreness was measured. Rebound jump height was impaired immediately after exercise, although significant only for CWI (CON: -12.4 cm, p = 0.083; CWI: -9.9 cm, p = 0.009). The CWI group demonstrated significant recovery of jump height at 24 h (+6.3 cm, p = 0.031) and 48 h (+8.9 cm, p = 0.002) compared to post-exercise. Ankle joint stiffness was decreased for CWI (-2.1 to -2.5 Nm/°, p = 0.005-0.041). Creatine kinase activity was similarly increased for both groups at 24 and 48 h, while there was also no group effect in muscle soreness (p ≥ 0.056). This pilot study demonstrates the potential for CWI to slightly enhance the recovery of DJ performance. However, this occurred in parallel with reduced ankle joint stiffness, signifying that jumps were performed with less efficiency, which would not be favorable for repeated SSC actions. While this should be confirmed with a larger sample size, this highlights the potential for CWI to be detrimental to the mechanical properties of the ankle joint. Therefore, future recovery intervention studies should concomitantly investigate variables contributing to performance, rather than just overall performance itself. 



#12 Moving Advertisements Systematically Affect Gaze Behavior and Performance in the Soccer Penalty Kick 

Reference: Front Sports Act Living. 2020 Jan 14;1:69. doi: 10.3389/fspor.2019.00069. eCollection 2019. 

Authors: Gareth Paterson, John van der Kamp, Geert Savelsbergh

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Summary: The aim of the current study was to investigate whether a moving advertisement positioned behind the goal area would influence the visual attention of participants performing a soccer penalty kick, and, whether this would an effect on subsequent motor performance. It was hypothesized that if the (moving) advertisement would function as a distractor, then this would result in non-specific disruptions in penalty performance measures, especially affecting aiming location and precision. Alternatively, it was reasoned that, in line with the Dunker illusion, the moving advertisement would systematically affect perception of target location, resulting in changes in penalty performance and aiming that are specific for the direction of motion of the advertisement. To test these hypotheses, we investigated the gaze behavior and kicking performance of intermediate skilled soccer players taking penalty kicks in three differing advertisement conditions, namely no advertisement, a stationary advertisement, and a moving advertisement. The latter condition consisted of an advertisement moving from left to right and an advertisement moving from right to left. Results showed that a moving advertisement placed behind the goal area indeed caught the visual attention of soccer penalty kickers using a goalkeeper-dependent kicking strategy. Participants kicking performance tended to be less variable within the no advertisement condition compared to the moving advertisement condition. In addition, systematic, direction-specific effects on aiming were found when comparing conditions in which the advertisement moved in opposite directions. This pattern of findings indicate that the accuracy of the penalty kick is impacted by task-irrelevant contextual information. 



#13 Sprint performance in football (soccer) players with and without a previous hamstring strain injury: An explorative  cross-sectional study

Reference: Int J Sports Phys Ther. 2020 Dec;15(6):947-957. doi: 10.26603/ijspt20200947. 

Authors: Lasse Ishøi, Kristian Thorborg, Per Hölmich, Kasper Krommes 

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Summary: Hamstring strain injuries are common in many sports. Following a hamstring injury, deficits in peak and explosive strength may persist after return to sport potentially affecting sprint performance. Assessment of repeated-sprint ability is recognized as an important part of the return to sport evaluation after a hamstring injury.Purpose: This purpose of this exploratory cross-sectional study was to compare sprinting performance obtained during a repeated-sprint test between football players with and without a previous hamstring strain injury. Forty-four fully active sub-elite football players, 11 with a previous hamstring strain injury during the preceding 12 months (cases; mean age, SD: 25.6 ± 4.4) and 33 demographically similar controls (mean age, SD: 23.2 ± 3.7), were included from six clubs. All players underwent a repeated-sprint test, consisting of six 30-meter maximal sprints with 90 seconds of recovery between sprints. Sprint performance was captured using high-speed video-recording and subsequently assessed by a blinded tester to calculate maximal sprint velocity, maximal horizontal force, maximal horizontal power, and mechanical effectiveness. A significant between-group difference was seen in favor of players having a previous hamstring injury over 6 sprints for maximal velocity (mean difference: 0.457 m/s, 95% CI: 0.059-0.849, p = 0.025) and mechanical effectiveness (mean difference: 0.009, 95% CI: 0.001-0.016, p = 0.020). Repeated-sprint performance was not impaired in football players with a previous hamstring strain injury; in fact, higher mean maximal sprinting velocity and better mechanical effectiveness were found in players with compared to without a previous hamstring injury. The higher sprinting velocity, which likely increases biomechanical load on the hamstring muscles, in previously injured players may increase the risk of recurrent injuries. 



#14 Worst case scenario match analysis and contextual variables in professional soccer players: a longitudinal study 

Reference: Biol Sport. 2020 Dec;37(4):429-436. doi: 10.5114/biolsport.2020.97067. Epub 2020 Jul 10. 

Authors: José M Oliva-Lozano, Daniel Rojas-Valverde, Carlos D Gómez-Carmona, Víctor Fortes, José Pino-Ortega

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Summary: This study aimed to describe the worst-case scenarios (WCS) of professional soccer players by playing position in different durations and analyse WCS considering different contextual variables (match half, match location and match outcome). A longitudinal study was conducted in a professional soccer team. Data were collected from different WCS durations in the total distance (TD), high-speed running distance (HSRD), and sprinting distance (SPD). A mixed analysis of variance was performed to compare different WCS durations between playing positions and contextual variables, making pairwise comparisons by Bonferroni post hoc test. Positional differences were found for TD (p < 0.01, ? p 2 = 0.02), HSRD (p < 0.01, ? p 2 = 0.01) and SPD (p < 0.01, ? p 2 = 0.02). There was a significant interaction when comparing WCS by match half in TD (F = 6.1, p < 0.01, ? p 2 = 0.07) but no significant differences in HSRD (p = 0.403, ? p 2 = 0) or SPD (p = 0.376, ? p 2 = 0). A significant interaction was identified when comparing WCS by match location in TD (F = 51.5, p < 0.01, ? p 2 = 0.14), HSRD (F = 19.15, p < 0.01, ? p 2 = 0.05) and SPD (F = 8.95, p < 0.01, ? p 2 = 0.01) as well as WCS by match outcome in TD (F = 36.4, p < 0.01, ? p 2 = 0.08), HSRD (F = 13.6, p < 0.01, ? p 2 = 0.04) and SPD (F = 7.4, p < 0.01, ? p 2 = 0.02). Positional differences exist in TD, HSRD, and SPD in match-play WCS, and contextual variables such as match half, match location and match outcome have a significant impact on the WCS of professional soccer players. 



#15 Accelerometry-based variables in professional soccer players: comparisons between periods of the season and playing positions 

Reference: Biol Sport. 2020 Dec;37(4):389-403. doi: 10.5114/biolsport.2020.96852. Epub 2020 Jul 10. 

Authors: Filipe Manuel Clemente, Rui Silva, Rodrigo Ramirez-Campillo, José Afonso, Bruno Mendes, Yung-Sheng Chen

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Summary: The aim of this study was to provide reference data of variation in external training loads for weekly periods within the annual season. Specifically, we aimed to compare the weekly acute load, monotony, and training strain of accelerometry-based measures across a professional soccer season (pre-season, first and second halves of the season) according to players' positions. Nineteen professional players were monitored daily for 45 weeks using an 18-Hz global positioning system to obtain measures of high metabolic load distance (HMLD), impacts, and high intensity accelerations and decelerations. Workload indices of acute load, training monotony, and training strain were calculated weekly for each of the measures. The HMLD had greater training strain values in the pre-season than in the first (p ≤ 0.001; d = 0.793) and second halves of the season (p ≤ 0.001; d = 0.858). Comparisons between playing positions showed that midfielders had the highest weekly acute load of HMLD (6901 arbitrary units [AU]), while central defenders had the lowest (4986 AU). The pre-season period was associated with the highest acute and strain load of HMLD and number of impacts, with a progressive decrease seen during the season. In conclusion, coaches should consider paying greater attention to variations in HMLD and impacts between periods of the season and between players to individualize training accordingly. 



#16 Biomechanical measures during two sport-specific tasks differentiate between soccer players who go on to anterior cruciate ligament injury and those who do not – a prospective cohort analysis

Reference: Int J Sports Phys Ther. 2020 Dec;15(6):928-935. doi: 10.26603/ijspt20200928. 

Authors: Celeste Dix, Amelia Arundale, Holly Silvers-Granelli, Adam Marmon, Ryan Zarzycki, Lynn Snyder-Mackler 

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Summary: Decelerating and cutting are two common movements during which non-contact anterior cruciate ligament (ACL) injuries occur in soccer players. Retrospective video analysis of ACL injuries has demonstrated that players are often in knee valgus at the time of injury. The purpose was too determine whether prospectively measured components of valgus collapse during a deceleration and 90 ° cut can differentiate between collegiate women's soccer players who go on to non-contact ACL injury. 51 NCAA women's soccer players completed motion analysis of a deceleration and 90 ° before the competitive season. Players were classified as Injured (noncontact ACL injury during the season) or Uninjured at the end of the season. Differences between groups for peak hip adduction, internal rotation, and knee abduction angles, and knee valgus collapse were analyzed with a MANOVA. Four non-contact ACL injuries were reported at the end of the season. There was a significant difference between groups for hip adduction angle during the 90 ° cut (p = 0.02) and deceleration (p = 0.03). Players who went on to ACL injury were in more hip adduction. Hip adduction angle is larger in players who go on to ACL injury than those who do not during two sport-specific tasks. The components of knee injury prevention programs that address proximal control and strength are likely crucial for preventing ACL injuries. 






Seasonal training and match load and micro-cycle periodization in male Premier League academy soccer players

The aim was to assess on pitch external loading of English Premier League (EPL) academy soccer players (U12-U18 age groups) over an entire competitive season.





The World’s Most Valuable Soccer Teams

Forbes has released its bi-annual list of the 20 most valued soccer teams.


The list includes nine teams from the English Premier League, four from the Italian Serie A, three from the Spanish La Liga, two from the German Bundesliga and one from each the Netherlands and France.

There is no real surprise inside the top ten, as the “usual” big teams are present. Ajax and Leicester premiered inside the top 20.


The revenues and operating income listed are for the 2019-2020 season in US dollar.


1. Barcelona

Value: $4.76 billion

Revenue (2020): $792 million

Operating Income (2020): $62.2 million

Debt Value: 6%


2. Real Madrid

Value: $4.75 billion

Revenue (2020): $792 million

Operating Income (2020): $92 million

Debt Value: 6%


3. Bayern Munich

Value: $4.215 billion

Revenue (2020): $703 million

Operating Income (2020):