Isokinetic torques and kicking maximal ball velocity in young soccer players

The purpose of this study is to assess if there is any correlation between isokinetic testing and field performance of young soccer players. The isokinetic peak torques of the knee extensor muscles in sitting position (T(KE)), and those of the hip flexor muscles in standing position (T(HF)) were measured in 24 junior soccer players. Four angular velocities (ω = 1.05, 3.14, 4.19, 5.23 rad · s-1 or 60, 180, 240, 300 deg · s-1) were used for the knee extensors and three (1.05, 3.14, 4.19 rad · s-1) for the hip flexors. On the field the subjects were asked to kick a stationary soccer ball as fast as possible against a barrier and the mean linear velocity over a 10 m path (v) was measured. T(KE) of the non dominant limb were higher than those of the opposite one at the three highest ω (p < 0.05). On the contrary the T(HF) of the dominant limbs were higher than those of the contralateral, at the two highest ω. When the ball was kicked by the dominant or non dominant limbs, the mean values and standard deviations (±SD) of v were 23.6 (±2.5) and 21.4 (±2.6) m · s-1. Torques and v were always positively correlated to each other; however, only in few cases was this relationship statistically significant. In conclusion the isokinetic torques do not seem to be good predictors of v, one of the several factors which determine the global performances of the soccer players.