The relationship between isokinetic performance of hip and knee and jump performance in university rugby players

OBJECTIVE: The aim of this study was to investigate how isokinetic lower limb strength and velocity of knee and hip extension correlate to vertical jump performance in university team rugby players. METHODS: Twenty asymptomatic university team rugby players performed a maximal vertical jump test, in which the vertical displacement was measured from maximum standing reach height to maximal height attained from a countermovement jump. A dynamometer assessed the maximal isokinetic strength and velocity of hip and knee extension in the dominant leg. Peak torque was measured when participants moved at angular velocities of 60 and 120°/s for hip extension, and 120 and 240°/s for knee extension. The highest velocity achieved during isokinetic hip and knee extension up to a maximum level of 360°/s was recorded. RESULTS: Moderately strong correlations were found between knee extension strength and vertical jump height, particularly when testing at faster angular velocities of 240°/s (R=0.609, p=0.002). There was also a significant moderate correlation between maximum knee extension speed and vertical jump height (R=0.540, p=0.007). CONCLUSIONS: The results suggest that focusing on strength/power training of the knee extensors at a high speed may result in improved vertical jump performance.