A control strategy for the execution of explosive movements from varying starting positions

1. Humans can execute explosive movements such as jumping and hitting an object irrespective of the starting position from which these movements have to be initiated; in fact, variability of kinematic parameters has been shown to decrease in the course of the movement. 2. We address the question of whether it is necessary to adapt the stimulation pattern of the muscles to such variations in starting position or whether the stabilizing effect of intrinsic muscle properties is such that one single muscle stimulation pattern might be used for a wide range of starting positions. 3. Specifically, we address this question for maximum-height human vertical squat jumping, using an approach based on mathematical modeling and computer simulation. The stimulation pattern of the muscles is the input of the model and the resulting movement is the output. 4. The optimal stimulation pattern for a starting position in the middle of the range of starting positions considered does not lead to adequate performance for other starting positions in that range. 5. However, a muscle stimulation pattern can be found that does result in close to optimal achievement for a wide range of starting positions. This muscle stimulation pattern, which is not optimal for any specific starting position, may be considered as "control that works" as opposed to "optimal control." 6. The latter muscle stimulation pattern also leads to adequate behavior for "new" starting positions both within and outside the range considered.