Purpose: 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. Methods: 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. Results: 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. Conclusion: 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.
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