Expectations may be for both legs to function identically during single- and double-leg vertical jumps. However, several reasons might prevent this from occurring. The goals of this investigation were twofold: assess the presence of side-to-side jump height differences during single-leg jumps in a homogenous group of healthy subjects and determine if those with a jump height asymmetry possessed consistent biomechanical differences during single- and double-leg jumps. Thirteen men and 12 women with competitive volleyball experience volunteered for the study. Significance was assessed at p < 0.05. The men jumped significantly higher than the women in all conditions and possessed differences in several anthropometric, kinematic, and kinetic parameters. Based on a three-jump average, all subjects had one leg that they could jump higher with (the dominant leg, DL). The men generated significantly greater maximum ground reaction forces and ankle joint powers on their DL whereas the women had no differences during the single-leg jumps. The only side-to-side differences that existed during the double-leg jumps were in the average ground reaction forces during propulsion. These findings suggest that equality of single-leg jump performance is the exception rather than the norm, with identification of consistent biomechanical attributes difficult within a group. Furthermore, any differences are not likely to cross over to other tasks, with men and women utilizing slightly different jump techniques.
The authors are with Health and Exercise Science, Colorado State University, Fort Collins, CO.