摘要：Purpose: The purpose of research was to compare strength parameters of lower limbs (knee extensors and flexors) and their asymmetries (bilateral and unilateral) in elite and sub-elite professional soccer players. Material and method: The screened sample was composed of two professional soccer teams. The first team (Team 1 – elite professional players, n = 28, age = 24.31 ± 4.79 years) was a leader of the first Czech league the second team (Team 2 – sub-elite professional players, n = 24, age = 26.19 ± 3.67 years) was a leader of the second Czech league. Maximum peak torque (PT) and derived parameters (bilateral ratio [Q:Q and H:H] and unilateral ratio [H:Q]) were evaluated using Cybex isokinetic dynamometer at three angular velocities (60, 180, 300 °·s -1 ) for the dominant (DL) and non-dominant leg (NL) during the knee flexion (KF) and extension (KE) in concentric contraction. The four-way mixed-design ANOVA, Student's t-test and Cohen "d" index of effect size were used for statistical analyses. Results: The factor of P (performance) revealed a significant effect on the level of isokinetic strength of lower limbs in soccer players (F (1.596) = 91.74, p < 0.01, η 2 = 0.14). The factors of L (laterality) did not significantly influence the level of thigh muscular strength of lower extremities in soccer players (F (1.596) = 2.47, p > 0.05, η 2 = 0.01). The factor of the tested muscle group (KE, KF) showed a significant effect on the compared bilateral differences (F (1.288) = 11.13, p < 0.01, η 2 = 0.04). Post-hoc tests also showed significantly higher (p < 0.01) values of the bilateral deficit in KF compared to KE. A significant effect was also found in the unilateral ratio of the lower limbs (H:Q) on the basis of comparison of the performance criterion (F (1.288) = 15.51, p < 0.01, η 2 = 0.05) and angular velocity of movement (F (2.288) = 5.56, p < 0.01, η 2 = 0.04). The unilateral ratio (H:Q) was significantly higher in both the dominant and non-dominant limbs in favour of the higher performance Team 1 in comparison to Team 2 (H:Q ratio dominant limb: F (1.144) = 5.87, p < 0.05, η 2 = 0.04; non-dominant limb: F (1.144) = 11.21, p < 0.01, η 2 = 0.07). Discussions and conclusions: The results of the study suggest that more than 50 % of players have at least one strength asymmetry regardless of their performance level. Elite professional players have greater muscular strength of KE and KF, especially at higher angular velocity. Concerning sub-elite players, we found a lower unilateral H:Q ratio. The results of the study point to worse preparedness of KF (performance and prevention perspective) in the sub-elite players. Maladaptive effects in terms of different kinds of body strength asymmetries represent a potential risk of a player's injury; therefore the detected asymmetries should be systematically monitored and compensated using specific exercises
