Effects of Load on Lower Extremity Joint Kinetics and Kinematics during Hexagonal Barbell Jump Squats

Strength and conditioning coaches often recommend athletes perform loaded jumps with an external load that maximizes peak power output to improve performance. However, there is debate regarding the training load that maximizes acute total body power, and power at individual lower extremity joints. The purpose of this study was to investigate lower extremity kinetic and kinematic variables across a spectrum of loads during jump squats using a hexagonal barbell. Participants performed jumps with a range of loads from 10% to 60% of hexagonal barbell deadlift estimated 1-repetition maximum (e1RM), as well as an unloaded countermovement jump. Using cameras and force plates, lower extremity angles, velocities, moments, powers, as well as total body power, were assessed for each jump. As load increased, there was a decrease in power at the total body level and the hip, but ankle power increased. All joint moment magnitudes increased with load, and flexion angle and velocity at the hip and knee decreased with load. Results suggest that increasing load impacts kinetic and kinematic variables and alters the jumping task, and that the majority of these changes occur when loading exceeds approximately 20-30% 1RM. Further, knee kinetics measures were most strongly related to total body power.