Anticipatory control in the initiation of a single step under biomechanical constraints in humans

It is generally known that both the duration and amplitude parameters of the anticipatory postural adjustments (APA) in the sagittal plane co-vary with the progression velocity in step or gait initiation. The purpose of this study is to elucidate how the duration and/or amplitude parameters of the APA are associated with the performance of the initiation of a single step forward in cases where the step displacement of the center of body mass are strictly regulated. Seven male subjects performed the initiation of a single step at two speeds (as fast as possible, F; normal speed, N). The APA amplitudes in the F condition showed significantly higher values than those in the N, while the APA durations showed no significant difference between the F and N conditions under the biomechanical constraints. The present results suggest that the central nervous system might scale the APA amplitudes and durations according to the intended forward velocity and the forward displacement of the center of body mass in step initiation, respectively.