(1) Background: The objective of the study was to check the relationship between laterality, amount of muscle mass (MM), and selected strength parameters on lower extremities and assessment of asymmetry like a result of training. (2) Methods: The screened sample consisted of soccer players (n = 65, age = 16.0 ± 1.2 years). The legs were assessed for MM, height of reflection on a force plate, and power over 30 s Wingate anaerobic test (WAnT). The relationships between the individual parameters and age dependence were assessed using a correlation analysis. The differences between the dominant and non-dominant leg were assessed using the t-test. (3) Results: A relationship between the jump height and the mean 30 s power in WAnT (r = 0.375, p ˂ 0.01) and between the amount of MM and the absolute power of the individual legs in WAnT (r = 0.695-0.832, p ˂ 0.01) was proved. A relationship between the take-off force and the MM, or between the MM and the relative power during a velocity force load was not found. (4) Conclusions: The amount of MM in young soccer players does not affect take-off force or strength power in WAnT. The more specific the movement is, the lower the effect on the achieved power output of the concerned MM. Differences in the performance between the dominant and non-dominant leg decrease with duration of the training.

Department of Mathematics Faculty of Education University of South Bohemia 371 15 České Budějovice Czech Republic

Department of Sports Studies Faculty of Education University of South Bohemia 371 15 České Budějovice Czech Republic

Sports Motor Skills Laboratory Faculty of Sports Physical Training and Education Charles University 165 52 Prague Czech Republic

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