Effect of Different Levels of Assisted Jumping on Countermovement Unloading Force and Velocity

Abstract

PURPOSE: The purpose of this study was to investigate the effect of elastic band assistance on VJ CM unloading force and velocity. METHODS: Thirty recreationally trained college men and women (M=15, W=15) completed three VJ testing sessions consisting of five conditions: 0%, 10%, 20%, 30%, and 40% body weight reduction (BWR). In all BWR conditions, subjects wore a full body harness while attached to two elastic cords suspended from the ceiling and performed three maximal VJ's with CM and arm swing on a force plate. In addition, a linear velocity transducer was attached to the subject's hip to determine the velocity-time curve. Percent unloading from body weight to minimal CM force and maximal CM velocity at each condition were recorded for analysis. RESULTS: Results indicated there were no sex by condition interactions (p>.05), but there were significant (p<.05) main effects for condition for both force and velocity. Countermovement unloading percentages were not different between 0% (64.62+22.51%) and 10% (70.75+14.41%), or between 20% (77.05+15.71%) and 30% (81.08+15.48%), or between 30% and 40% (83.88+13.79) BWR. Both 30% and 40% were greater than 10% and 0%, but only 40% was greater than 20%. CM velocities under all elastic conditions were significantly faster than 0% (0%=.99+.25 m/s, 10%=1.19+.26 m/s, 20%=1.24+.30 m/s, 30%=1.29+.26 m/s, 40%=1.23+.17 m/s). Only 30% was significantly faster than 10%. CONCLUSIONS: These data suggest that assisted jumping alters countermovement mechanics. Therefore, future research should investigate the chronic effects of assisted jumping on normal bodyweight VJ performance.