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. 


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