Effect of load positioning on the kinematics and kinetics of weighted vertical jumps.

One of the most popular exercises for developing lower-body muscular power is the weighted vertical jump. The present study sought to examine the effect of altering the position of the external load on the kinematics and kinetics of the movement. Twenty-nine resistance-trained rugby union athletes performed maximal-effort jumps with 0, 20, 40 and 60% of their squat 1RM, with the load positioned as follows: 1) on the posterior aspect of the shoulder using a straight barbell (SBJ); and 2) at arms length using a hexagonal barbell (HBJ). Kinematic and kinetic variables were calculated through integration of the vertical ground reaction force data using a forward dynamics approach. Performance of the HBJ resulted in significantly (p < 0.05) greater values for jump height, peak force, peak power and peak rate of force development, compared to the SBJ. Significantly (p < 0.05) greater peak power was produced during the unloaded jump compared to all trials where the external load was positioned on the shoulder. In contrast, significantly (p < 0.05) greater peak power was produced when using the hexagonal barbell combined with a load of 20% 1RM compared to all other conditions investigated. The results suggest that weighted vertical jumps should be performed with the external load positioned at arms length rather than on the shoulder when attempting to improve lower-body muscular performance