Voluntary and involuntary adaptation of walking to temporal and spatial constraints

The effects of voluntary adaptations of the walking pattern were studied in 10 healthy subjects. These subjects had to adapt their walking pattern to external cues that resulted in either temporal or spatial constraints on walking. The results show that whereas the normal walking pattern in each subject was characterized by a stable linear relationship between step frequency and step length, the adaptation of walking to external cues resulted in two different modes of walking: frequency modulation with a constant amplitude of leg movements in rhythmic walking, and amplitude modulation with a constant frequency of leg movements in walking with visually guided step length. The relative timing of support, swing, and double-support phases was remarkably different between the two conditions; only with changes in step length a change in the relative timing of these phases could be observed. The different modes of walking could not be explained by the nature of the constraints imposed by the instruction to adapt the walking pattern to the external cues. It can be concluded that the way step frequency and step length are controlled involuntarily varies with the employed voluntary strategies. The different modes of walking suggest the existence of specific supraspinal influences on lower level pattern generating mechanisms. The involuntary adaptation of the relative timing within the stride cycle may result from the interaction between (low level) central processes and the dynamics of the movement.