Relationship of Isokinetic Leg Press Force with Jumping Performance and 1RM in the Squat

Muscle strength and power are important requirements in many sports. The correlation of jumping performance as manifestation of muscle power and squatting one-repetition maximum (1RM) has been shown in several investigations. Correlations with maximum force in a linear isokinetic leg press are still pending. Since different testing devices produce different relationships and rotational isokinetic measurements show conflicting results, further evidence is needed.

We investigated the correlation of isokinetic leg press force at 0.1 m/s and 0.7 m/s with squat 1RM and jumping performance in different vertical jumps.

The results show medium to strong, significant correlations for isokinetic force at 0.1 m/s with squat- and countermovement-jump performance, whereas isokinetic force at 0.7 m/s showed strong, significant correlations for both jumping tests. Drop jump performance (dropping heights: 20, 30, 40, and 50 cm, respectively) reveals weak to medium, significant correlations with isokinetic force at 0.1 m/s and weak, significant correlations with isokinetic force at 0.7 m/s. Squat 1RM displays strong relationships to isokinetic force with greater coefficients regarding higher movement speed in the isokinetic condition.

The maximum strength of the leg extensors displays a basic requirement for vertical jumping with great motion in knee- and hip-joints and should be considered in training programs. For vertical jumps that are mainly generated via ankle motion, maximum strength of knee- and hip-extensors plays an indirect role to guarantee for performance-enhancing mechanisms. Additionally, in strength testing, different manifestations of strength performance should carefully be taken into account.