The Effect of Initial Knee Angle on Concentric-Only Squat Jump Performance

Purpose: There is uncertainty as to which knee angle during a squat jump (SJ) produces maximal jump performance. Importantly, understanding this information will aid in determining appropriate ratios for assessment and monitoring of the explosive characteristics of athletes. Method: This study compared SJ performance across different knee angles--90 degrees, 100 degrees, 110 degrees, 120 degrees, 130 degrees, and a self-selected depth--for jump height and other kinetic characteristics. For comparison between SJ and an unconstrained dynamic movement, participants also performed a countermovement jump from a self-selected depth. Thirteen participants (M[subscript age] = 25.4 ± 3.5 years, M[subscript height] = 1.8 ± 0.06 m, M[subscript weight] = 79.8 ± 9.5 kg) were recruited and tested for their SJ performance. Results: In the SJ, maximal jump height (35.4 ± 4.6 cm) was produced using a self-selected knee angle (98.7 ± 11.2 degrees). Differences between 90 degrees,100 degrees, and self-selected knee angles for jump height were trivial (ES ± 90% CL = 90 degrees-100 degrees 0.23 ± 0.12, 90 degrees-SS -0.04 ± 0.12, 100 degrees-SS -0.27 ± 0.20; 0.5-2.4 cm) and not statistically different. Differences between all other knee angles for jump height ranged from 3.8 ± 2.0 cm (mean ± 90% CL) to 16.6 ± 2.2 cm. A similar outcome to jump height was observed for velocity, force relative to body weight, and impulse for the assessed knee angles. Conclusions: For young physically active adult men, the use of a self-selected depth in the SJ results in optimal performance and has only a trivial difference to a constrained knee angle of either 90° or 100°.