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-age = 25.4 +/- 3.5 years, M-height = 1.8 +/- 0.06m, M-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 degrees or 100 degrees.