Abstract
The aim of the present study was to determine the relationship between vertical jump performance and the isokinetic strength of the knee extensors in professional soccer players at the end of the of the competition period, after the detraining period (before the initiation of the preparatory period) and after the completion of the preparatory period. Eighteen professional soccer players participated in the present study. The peak jumping height (of the squat and counter movement jumps on an Ergojump device) was used as indicator of vertical jump performance. The subjects also performed three submaximal and three maximal isokinetic efforts of the knee extensors at angular velocities of 60 and 180°/s. Pearson product moment correlation analyses were conducted to determine the relationship between isokinetic strength and jumping parameters. The significance level was set at p < 0.05. The analysis indicated that jumping height was moderately correlated with the knee torques at the test velocities after the competition and preparatory period.