Determining the Threshold of Unweighting in Squat Jumps: A Study on Jump Height and Unweighting Amplitude.

Abstract: Agar-Newman, DJ, Funk, S, Cavin, E, Geneau, MC, Tsai, MC, and Klimstra, M. Determining the threshold of unweighting in squat jumps: a study on jump height and unweighting amplitude. J Strength Cond Res 39(3): 295-299, 2025-Squat jumps (SJs), involving only an upward propulsive phase, are commonly used in athletic assessment and research. Unfortunately detecting an unweighting phase before the upward propulsive phase is typically done subjectively by observing the athlete or inspecting the force-time trace, and there is no clearly established threshold of unweighting for a valid SJ. This reliance on subjectivity to determine a valid SJ has the potential to result in misleading findings or incorrect training interventions. Therefore, the aim of this study was to determine at what threshold of unweighting does SJ height increase. To answer this question, 56 female athletes, mean (±SD) body mass (BM) 76.26 ± 12.40 kg, height 1.68 ± 0.06 m, age 22.23 ± 1.47 years performed 936 SJs, under 4 different external loads. Squat jumps were divided into 6 separate groups based on the amplitude of unweighting relative to BM and an analysis of covariance was run with jump height as the dependent variable, unweighting group as the fixed factor, and external load as a covariate. There was a significant difference in jump height (F (5,930) = 13.65, p < 0.01) between unweighting groups while controlling for external load. Post hoc testing using Dunnett test showed that all SJ unweighting thresholds >2% BM (p < 0.01) resulted in an increased jump height from the threshold of ≤1% BM. Therefore, to maintain the validity of SJs as a measure, a threshold of 2% BM for unweighting amplitude is recommended. Adhering to this threshold will eliminate subjectivity in identifying valid SJs and potentially enable practitioners to automate the process using algorithms.