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To assess the inter-machine reliability of the Biodex System 3 Pro and Cybex Humac Norm Model 770 dynamometers for knee extensor and knee flexor peak torque measurements in isometric, concentric and eccentric tests. Randomized/crossover. Exercise Research Laboratory, Federal University of Rio Grande do Sul (Brazil). 25 healthy male subjects. Isometric, concentric and eccentric knee extensor and knee flexor peak torques recorded in the same test procedure performed on both isokinetic dynamometers. One-way ANOVA, intraclass correlation coefficient (ICC), standard error of measurement (SEM) and coefficient of variation (CV) were used to verify significant differences, relative and absolute reliability between devices. No significant differences were found between tests performed on Biodex and Cybex (p > 0.05). ICC values indicated a high to very high reproducibility for isometric, concentric and eccentric peak torques (0.88–0.92), and moderate to high reliability for agonist-antagonist strength ratios (0.62–0.73). Peak torque did not show great difference between dynamometers for SEM (3.72–11.27 Nm) and CV (5.27–7.77%). Strength ratios presented CV values of 8.57–10.72%. Maximal knee extensor and knee flexor tests performed in isometric (60° of knee flexion), concentric and eccentric modes at 60°/s in Biodex and Cybex dynamometers present similar values. •Knee extensor/flexor tests were performed using Biodex and Cybex isokinetic dynamometers.•Isometric peak torque measures were similar between devices.•Concentric and eccentric peak torque measures were similar between devices.•Conventional and functional ratios were similar between devices.

Purpose The purpose of this study was to assess if differences in hamstring strength, hamstring-to-quadriceps (H:Q) strength ratio, and biceps femoris long head (BF LH ) fascicle length exist between male and female professional football (soccer) players. Methods One-hundred professional footballers participated in this cross-sectional study: 50 men and 50 women. Ultrasound images of BF LH muscle and isokinetic dynamometry tests were performed. Results Men were stronger than women for hamstring concentric (2.01 ± 0.21 Nm/kg vs. 1.55 ± 0.23 Nm/kg; p  < 0.001; large effect size, 2.08) and eccentric (2.87 ± 0.45 Nm/kg vs. 2.39 ± 0.32 Nm/kg; p  < 0.001; large effect size, 1.23) peak torques. There was no sex-related difference for H:Q conventional ratio (concentric/concentric; 0.55 ± 0.06 vs. 0.55 ± 0.07); but women presented greater H:Q functional ratio (eccentric/concentric; 0.78 ± 0.12 vs. 0.85 ± 0.09; p  = 0.003; moderate effect size, 0.66). Men and women presented similar BF LH fascicle length: 0.24 ± 0.05 vs. 0.23 ± 0.05 (values normalized by muscle length). Conclusions Among the muscular factors assessed in this study, men presented stronger hamstring muscles, women presented greater H:Q functional ratio, and there was no sex-related differences for H:Q conventional ratio or BF LH fascicle length.

To describe the changes in hip adductor strength of professional women's football players over a season. One-season prospective study. Facilities of a national first division club. Professional women's football players. Maximum hip adductor isometric strength in the long-lever and short-lever positions at four timepoints: early preseason, early season, mid-season, and end-season. Twenty-two players completed the study. Hip adductor strength values in early preseason (134 ± 29 N in the long-lever position and 317 ± 68 N in the short-lever position) were significantly lower than in the early season (171 ± 29 N and 363 ± 54 N) and mid-season (163 ± 23 N and 369 ± 53 N). By the end of the season (150 ± 19 N and 345 ± 39 N), strength values had significantly declined from both early and mid-season levels. Visual inspection of individual athletes' strength evolution over time reveals heterogeneous responses, with some players showing trajectories opposite to the group at specific time points. Hip adductor strength increased from the preseason to the start of the women's football national league, remained stable during the first half of the league, but slightly declined in the second half. The heterogeneous responses among athletes underscore the importance of individualized monitoring throughout the season. •Hip adductor strength increased from the preseason to the early season.•Hip adductor strength remained stable during the first half of the national league.•Hip adductor strength slightly declined in the second half of the national league.•Players' strength evolution over time reveals heterogeneous responses.

This study aimed at verifying the effect of a football match on the eccentric knee flexor strength of male professional players along a 72-h period. Quasi-experimental study. Football club facilities. Fifteen players were assessed in four timepoints: 24 h before, immediately after, 48 h and 72 h after the match. The eccentric knee flexor strength was assessed during the Nordic hamstring exercise execution. Players presented a significant strength reduction immediately after match (Δ = 12%; p = 0.001; large effect size, d = 1.10), and did not recover their strength capacity within a 48 h-period (Δ = 6%; p = 0.011; moderate effect size, d = 0.57). At 72 h after the match, strength was similar to baseline levels (Δ = 3.5%; p = 0.122; small effect size, d = 0.34). Secondarily, individual response analysis considered a player ‘fully recovered’ when his strength deficit compared to the baseline measure was lower than the measurement coefficient of variation (i.e., <5%). Only 6 (40%) and 9 (60%) players were ‘fully recovered’ at 48 h and 72 h after the match, respectively. Professional football players experienced an immediately post-match drop on the eccentric knee flexor strength, and significant strength deficits persisted for a 48-h period. Some players were not recovered at 72 h after the match. •Eccentric knee flexor strength was reduced immediately after a professional football match.•Significant eccentric knee flexor strength deficits persisted at 48 h after match.•Players demonstrated individual post-match recovery profiles.

Purpose Given the controversial use of the Acute:Chronic Workload Ratio (ACWR) in determining the availability of soccer players for training and matches, this study aimed at verifying how many professional soccer players had an ACWR above 1.5 (considered a ‘danger zone’) immediately before the exposure (training or match) in which they sustained a hamstring muscle injury. Methods Forty-eight male soccer players of a professional team were monitored through global positioning system (GPS) in this 2-season retrospective study (10 participated in both seasons and 38 in a single season). The ACWR of total distance, high-speed running distance, very high-speed running distance, and the number of actions performed >19 km/h were calculated before all hamstring injuries and included in the analysis. Results Twenty players sustained hamstring injuries. There was no time effect on the group’s daily workload or the average workload over the 4 weeks before the injury ( p  > 0.05). Fifteen players (i.e., 75%) had ACWR below 1.5 for the four GPS metrics immediately before the training or match in which they sustained a hamstring injury. Five players (25%) were classified in the ‘danger zone’ (i.e., ACWR > 1.5) for the very high-speed running distance; 3 of these players were also in the ‘danger zone’ for high-speed running distance and the number of actions >19 km/h, and 2 players for the total distance. Conclusion Since three-quarters of the hamstring injuries affecting professional soccer players were preceded by ACWR values below 1.5 in all GPS metrics, it is prudent for medical/coaching staff exercise caution when considering the ACWR ‘danger zone’ as the primary metric for determining player availability for training or matches.

Background Muscular responses to training programs with the Nordic hamstring exercise (NHE) have been widely investigated to understand its preventive effects on muscle strain injury. Conversely, little is known about muscular responses to the stiff-leg deadlift (SLD), an exercise that preferably activate the biceps femoris long head, precisely the knee flexor muscle most commonly injured. Aims The aim of the current study was to verify the effect of training programs using the NHE or the SLD on muscle architecture, strength, and functional performance of well-trained rugby players. Methods Twenty-three male rugby union players completed a 5-week training program using either the NHE ( n  = 12) or the SLD ( n  = 11). Biceps femoris long head muscle architecture, hamstring and quadriceps isokinetic peak torques, and countermovement jump performance were assessed before and after the training program. Results There was no significant group-by-time interaction for any outcome ( p  > 0.05). NHE group experienced higher percent increases than SLD group for biceps femoris fascicle length (~ 14% vs. ~ 6%; p  = 0.015). Within-group analysis indicated that NHE group presented greater effect sizes for muscle architecture outcomes, hamstring eccentric peak torque and hamstring-to-quadriceps functional ratio; conversely, SLD group presented greater effect sizes for hamstring concentric peak torque and countermovement jump height. Conclusions The NHE should preferably be used to enhance the hamstring eccentric strength and the biceps femoris fascicle length (our primary outcomes, supported by previous studies as risk factors for hamstring strain injury), while the SLD favor improvements in hamstring concentric strength and jump performance.

Background Female soccer players have a higher anterior cruciate ligament (ACL) injury rate than male players, possibly due to sex-specific intrinsic risk factors. The Landing Error Scoring System (LESS) and the Step-Down Test (SDT) have been used for screening the ACL injury risk, but the performance of adult soccer players in these field-based tests remains unclear. Purpose To compare the performance of well-conditioned male and female soccer players on two field-based tests for screening the ACL injury risk: the LESS and the SDT. Methods Sixty-seven soccer players from first state division teams were part of this study: 36 men (20 ± 1 years) and 31 women (21 ± 2 years). All players had no ACL injury history, and performed both tests in their clubs’ facilities. Results No significant difference between groups was found for total score on the LESS [male = 2.56 ± 1.25 (2.14; 2.98); female = 2.81 ± 1.64 (2.21; 3.41); p  = 0.779] or the SDT [male = 2.61 ± 1.02 (2.26; 2.96); female = 2.97 ± 0.95 (2.62; 3.32); p  = 0.280]. A greater percentage of females counted “errors” related to knee medialization and trunk-flexion displacement during LESS execution, while males failed more often in relation to foot positioning. Distribution of “errors” on the SDT was similar between sexes. Conclusions Male and female professional soccer players presented similar total scores in the LESS and the SDT. However, female players seem to present some landing features potentially harmful to the ACL (related to dynamic knee valgus and poor trunk-flexion displacement) more often than males. Level of evidence 3a.