Control of maximal and submaximal vertical jumps.

Abstract

It was investigated to what extent control signals used by human subjects to perform submaximal vertical jumps are related to control signals used to perform maximal vertical jumps. Eight subjects performed both maximal and submaximal height jumps from a static squatting position. Kinematic and kinetic data were recorded as well as electromyographic (EMG) signals from eight leg muscles. Principal component analysis was used analyze the shape of smoothed rectified EMG (SREMG) histories. Jumps were also simulated with a forward dynamic model of the musculoskeletal system, comprising four segments and six muscles. First, a maximal height jump was simulated by finding the optimal stimulation pattern, i.e., the pattern resulting in a maximum height of the mass center of the body. Subsequently, submaximal jumps were simulated by adapting the optimal stimulation pattern using strategies derived from the experimental SREMG histories. SREMG histories of maximal and submaximal jumps revealed only minor differences in relative timing of the muscles between maximal and submaximal jumps, but SREMG amplitude was reduced in the biarticular muscles. The shape of the SREMG recordings was not much different between the two conditions, even for the biarticular muscles. The simulated submaximal jump resembled to some extent the submaximal jumps found in the experiment, suggesting that differences in control signals as inferred from the experimental data could indeed be sufficient to get the observed behavior. The results fit in with theories on the existence of generalized motor programs within the central nervous system, the output of which is determined by the setting of parameters such as amplitude and relative timing of control signals.