Background and objective: Type of physical activity may influence morphological and muscular asymmetries in the young population. However, less is known about the size of this effect when comparing various sports. The aim of this study was to identify the degree of bilateral asymmetry (BA) and the level of unilateral ratio (UR) between isokinetic strength of knee extensors (KE) and flexors (KF) among athletes of three different types of predominant locomotion in various sports (symmetric, asymmetric and hybrid). Material and methods: The analyzed group consisted of young elite athletes (n = 50). The maximum peak muscle torque of the KE and KF in both the dominant (DL) and non-dominant (NL) lower limb during concentric muscle contraction at an angular velocity of 60°·s⁻¹ was measured with an isokinetic dynamometer. Results: Data analysis showed a significant effect of the main factor (the type of sport) on the level of monitored variables (p = 0.004). The type of sport revealed a significant difference in the bilateral ratio (p = 0.01). The group of symmetric and hybrid sports achieved lower values (p = 0.01) of BA in their lower limb muscles than those who played asymmetric sports. The hybrid sports group achieved higher UR values (p = 0.01) in both lower limbs. Conclusions: The results indicate that sports with predominantly symmetrical, asymmetrical, and hybrid types of locomotion affected the size of the BA, as well as the UR between KE and KF in both legs in young athletes. We recommend paying attention to regular KE and KF strength diagnostics in young athletes and optimizing individual compensatory exercises if a higher ratio of strength asymmetry is discovered.

The aim of this study was to examine the differences in the weekly training load between starters and non-starters classified based on the match starting line-up, with respect to the playing position and a training day. Notably, 31 young adult soccer players (age: 18.79 ± 1.04 years) competing in the 3rd Czech division were monitored across the season. The weekly training load was measured using a GPS system as follows: total distance covered (TD), high-speed running distance (HSR), sprint running distance (SR), and acceleration and deceleration distance (ACDC). We found higher values in three out of four observed variables (HSR, SR, and ACDC, excluding TD) for starters compared to non-starters (p < 0.05), with small to moderate effect sizes (d = 0.40–0.49). Differences were observed especially in players who were fullbacks, offensive midfielders, and forwards. Moreover, the largest differences were found in training prior to a match day for HSR, SR, and ACDC (p < 0.05). Non-starters experienced lower weekly external loads in offensive player positions, predominantly in high-intensity variables, which are essential for their physical performance. It seems that non-starters may experience potential under-loading in the training process. Coaches and practitioners should be aware of this potential risk and find an appropriate method to compensate for load discrepancies, particularly in terms of high-intensity activities.

The strength asymmetry of athletes as a negative health and performance factor is increasingly being researched in sports with a high load on the dominant limb when some specific unilateral movements, such as passing, jumping, and tackling, are required. This study aimed to determine the level of isokinetic strength bilateral asymmetry (BA) among knee extensors (KEs) and knee flexors (KFs) of elite youth soccer players. The sample (n = 87) consisted of three age categories of under 13 (U13), under 15 (U15), and under 17 (U17) years old. Isokinetic dynamometry was used to obtain the maximum peak torque of the KEs and KFs in the dominant and non-dominant lower limbs during concentric muscle contraction. The analysis revealed significantly lower values (p < 0.05) of BA in KEs in U17 than in younger categories, U13 and U15, and higher values (p < 0.05) of BA in KFs in the U15 category than in the U17category. The majority of the players in the U15 category (68%) reached KFs BA higher than 10% in comparison with U13 players (50%) and U17 players (28% of players) (p < 0.05). Our results showed a significant effect of age category on BA levels in young soccer players. High incidences of increased BA in the lower limbs occurred in the younger categories (U13, U15) and subsequently decreased in the later adolescent stages.

Background and Objectives: The aim of this study was to identify preseason isokinetic strength differences in the knee flexors and extensors and their ipsilateral/bilateral ratios and, furthermore, to compare the results among players who subsequently overcame a hamstring strain injury (HSI) or anterior cruciate ligament (ACL) rupture during the season and those who did not. Materials and Methods: A total of 134 professional soccer players underwent isokinetic strength assessment at a velocity of 60°·s⁻¹ (knee flexors and extensors) for the dominant and non-dominant lower limb to determine preseason peak torque values and bilateral and ipsilateral strength ratios. Subsequently, the incidence of injuries during the season was recorded, and players were divided into groups according to ACL rupture injuries (n = 10), hamstring strains (n = 10), and a control group of non-injured players who were selected on a random basis (n = 20). A retrospective approach was used to analyze and compare the preseason strength characteristics and whether some variance among groups was relevant among the injured leg and non-injured leg groups. Results: The results of our study show that low-angular velocity preseason testing did not result in a player’s HSI or ACL injury during the season. The difference between the monitored groups ranged from 1.5% to 3%. The comparison showed low evidence for significant differences. Conclusions: An angular velocity of 60°·s⁻¹ within concentric muscle contraction alone was not linked to subsequent injury of the hamstring or anterior cruciate ligament and acted as an insufficient factor of injury risk in adult professional soccer players.

Purpose : This scoping review aimed to synthesize and map the evidence on nutritional and supplementary strategies used to enhance postexercise recovery in soccer players. Specifically, it sought to (1) identify effective interventions across physical, physiological, perceptual, and biochemical outcomes; (2) describe methodological designs; and (3) highlight research gaps for future investigation. Methods : Following Cochrane and PRISMA-ScR guidelines, 4 databases (PubMed, Web of Science, Scopus, SportDiscus) were searched without date limits. Eligible studies included randomized controlled trials involving adult soccer players (≥18 y) that examined nutritional or supplementary interventions administered within 72 hours postmatch or after an exercise-induced muscle damage protocol. Data extraction, synthesis, and a risk-of-bias assessment were performed independently by 2 reviewers. Results : Eleven studies (n = 135 players) met inclusion criteria. Interventions included carbohydrates, proteins (casein, whey, and milk protein), tart cherry juice, curcumin, caffeine, and ketones. The most frequently assessed outcomes were physical (jumping, sprinting, and strength) and perceptual (muscle soreness, and well-being), while biochemical and physiological measures were less common. Curcumin (500 mg·d ⁻¹ ) and presleep casein supplementation (40 g) demonstrated beneficial effects on physical and perceptual recovery markers up to 36 hours postmatch in professional soccer players. In contrast, carbohydrates, caffeine, and milk protein showed inconsistent or negligible effects. Most studies (82%) presented a high risk of bias, small sample sizes, and heterogeneous methodologies. Conclusions : Current evidence on nutritional and supplementary recovery strategies in soccer is limited and methodologically weak. Curcumin and casein show the most promise for enhancing short-term recovery. Future research should include well-controlled trials with standardized protocols, larger samples, and inclusion of female players to inform evidence-based recovery nutrition in soccer.

Kalata, M, Lukavsky, J, Martinho, DV, Williams, CA, Konarski, JM, Zahalka, F, Malina, RM, and Maly, T. Trajectories of 10 m sprint time and countermovement jump height relative to peak height velocity in male youth soccer players. J Strength Cond Res XX(X): 000–000, 2026—To characterize the longitudinal development of 10 m sprint time and countermovement jump (CMJ) height across adolescence in youth male soccer players. Twenty academy players (10.9–16.0 years) were assessed longitudinally over 4–5 years, comprising 145 CMJ and 140 sprint observations. Age at peak height velocity (PHV) for each player was estimated from longitudinal stature records collected at 6-month intervals, by identifying the interval of maximal annual growth and noting its midpoint. Developmental trajectories were aligned relative to years from PHV (Δage) and analyzed using Generalized Additive Mixed Models. Inference was based on estimated trajectories and associated uncertainty. Countermovement jump performance followed a nonlinear trajectory, with a maximal rate of improvement occurring shortly after PHV (+0.20 years; +3.06 cm·y ⁻¹ ). By contrast, early acceleration improved at a relatively constant rate across the observed maturity interval (∼0.04 seconds·y ⁻¹ ), with no clear nonlinear feature around PHV in this data set. No significant relationship was noted between the individual CMJ and 10 m sprint gains ( r = 0.04; p = 0.80). The existence, timing, and magnitude of accelerated development of these motor skills are task-specific. Peak height velocity–aligned monitoring may help contextualize periods of more rapid CMJ development in this cohort, whereas sprint acceleration followed a more gradual trajectory across adolescence.