Comparison of Different Take-off Thresholds When Assessing Vertical Jump Performance.

Abstract

Reliably determining vertical jump (VJ) take-off on a force plate is crucial when identifying performance-related biomechanical factors. Therefore, the purpose of this study was to compare several take-off thresholds (20 N, 10 N, 5 N, 1 N, five standard deviations above an unloaded force plate (5SD), and peak residual force (PkRes) produced when the force plate was unloaded) in terms of jump height (JH), movement time (MT), reactive strength index modified (RSImod), net impulse (netIMP), and propulsive impulse (prIMP). Twenty-one participants performed five countermovement VJs on a force plate. All thresholds were reliable with intraclass correlations ≥ 0.835 and coefficient of variation < 10%. Our results show significant differences across the different take-off thresholds for JH, MT, RSImod, netIMP, and prIMP. However, these differences were considered trivial based on effect sizes. While differences in these thresholds may not be practically meaningful, practitioners are encouraged to consider the noise in the force-time signal and select an appropriate threshold that matches PkRes within their given environment.