Dynamics of pushing

A standing individual can use several strategies for modulating pushing for ce magnitude. Using a static model, researchers have shown that the efficac y of those strategies varies considerably. In the present article, the auth ors propose a human motor control dynamic model for analyzing transients th at occur when an individual is asked to modulate force magnitude. According to the model, the impedances of both the upper and the lower limbs influen ce the time course of force variations and foot placement has a profound ef fect on pushing force dynamics. With a feet-together posture, the center of pressure has a limited range of motion and changes in force may be precede d by initial changes in the opposite direction; that is, to decrease force, an individual must first increase force. When the feet are placed apart, i ndividuals can move the center of pressure over a much larger range, thereb y modulating pushing force magnitude, without reversing behavior, over a la rger range of force magnitudes. Therefore, the best way to control pushing force at the hand may be by using the foot.