Acute Jump Performance Responses Following Isometric Squats Performed at Full and Half Squat Depths

Aim: The aim of this study was to determine the influence of squat depth during an isometric conditioning activity on the magnitude and time course of acute changes in countermovement jump (CMJ) performance. Methods: In a parallel-group design, twenty-four resistance-trained males performed three 4-s maximal voluntary contractions using either a maximal-depth squat or a half-squat (~90° knee angle). CMJ height was assessed before the conditioning activity and at 3, 6, 9, and 12 min post-activation. Data were analyzed using a two-way mixed-model ANOVA, and simple linear regression analyses were performed to examine whether relative strength, training experience, and weekly training volume were associated with the magnitude of CMJ performance changes. Results: A significant main effect of time was observed for CMJ performance (F = 7.81, p < 0.001, ηp2 = 0.26). Post hoc comparisons showed significantly greater CMJ performance at 6 min (p < 0.001; ES = 0.96) and 9 min (p = 0.008; ES = 0.80) compared with baseline. In addition, CMJ performance at 6 min (p = 0.021; ES = 0.71) and 9 min (p = 0.028; ES = 0.69) was significantly greater than at 3 min post-activation, whereas no significant differences were observed between baseline and 3 min or 12 min. No significant main effect of squat depth (F = 0.003, p = 0.958, ηp2 < 0.001) or time × squat depth interaction (F = 0.58, p = 0.650, ηp2 = 0.03) was found. Conclusions: These findings indicate that squat depth during maximal isometric conditioning activity did not significantly influence either the magnitude or the temporal pattern of post-activation changes in CMJ performance. Greater CMJ values were observed 6–9 min after the conditioning activity, suggesting that, within the tested protocol, recovery timing may be of greater practical importance than squat depth when implementing isometric conditioning strategies to enhance jump performance.