Adaptability of the human stride cycle during split-belt walking

Abstract

The adaptation of leg movements to split-belt conditions was studied during treadmill walking in 10 healthy subjects. Four different belt speeds (0.5/1.0/1.5/2.0 m/s) were offered in all possible combinations for the left and right leg. All subjects automatically adapted to split-belt conditions. Although in all subjects and in all conditions the adaptation of leg movements within the stride cycle resulted in a walking pattern, the stepping pattern in conditions with extreme speed differences could be best described as limping. Regardless of the speed combination offered to the left and right leg, the adaptation to differences in left and right belt speed always involved: (1) Changes in stride cycle duration. The stride frequency in split-belt conditions was always intermediate to the values found during normal walking at speeds corresponding to the left and right belt speeds. There was a tendency towards the normal value of the faster belt, however. (2) An asymmetrical adaptation of the amplitude of leg movements. The support length of a leg generally tended towards the normal value for the speed offered to this leg. Thus, within the same cycle duration, the leg on the faster moving belt always made larger amplitudes than the slower leg. (3) An altered timing of support, swing and double support durations within the stride cycle. An increase in the relative duration of the support phase of the slower leg and the swing phase of the faster leg allowed for the larger amplitude of leg movements of the faster leg. Contrary to the asymmetric adaptation in support and swing durations the adaptation in the durations of both double support periods were more or less symmetric. The results of this split-belt walking study point to a high degree of flexibility in the relative timing of leg movements during walking. It is argued that the adaptation to split-belt conditions involves the tuning of low level coordinative mechanisms to the specific task requirements during split-belt walking by means of the afferent feedback resulting from the movement pattern.