The contribution of light touch sensory cues to corrective reactions during treadmill locomotion.

The arms play an important role in balance regulation during walking. In general, perturbations delivered during walking trigger whole-body corrective responses. For instance, holding to stable handles can largely attenuate and even suppress responses in the leg muscles to perturbations during walking. Particular attention has been given to the influence of light touch on postural control. During standing, lightly touching a stable contact greatly reduces body sway and enhances corrective responses to postural perturbations, whereas light touch during walking allows subjects to continue to walk on a treadmill with the eyes closed. We hypothesized that in the absence of mechanical support from the arms, sensory cues from the hands would modulate responses in the legs to balance disturbing perturbations delivered at the torso during walking. To test this, subjects walked on a treadmill while periodically being pulled backwards at the waist while walking. The amplitude of the responses evoked in tibialis anterior to these perturbations was compared across 4 test conditions, in a 2 × 2 design. Subjects either (a) lightly touched or (b) did not touch a stable contact, while the eyes were (c) open or (d) closed. Allowing the subjects to touch a stable contact resulted in a reduction in the amount of fore-aft oscillation of the body on the treadmill, which was accompanied by a reduction in the ongoing electromyographic activity in both tibialis anterior and soleus during undisturbed walking. In contrast, the provision of touch resulted in an increase in the amplitude of the evoked responses in tibialis anterior to the backward perturbations that was more evident when subjects walked with the eyes closed. These results indicate that light touch provides a sensory cue that can be used to assist in stabilizing the body while walking. In addition, the sensory information provided by light touch contributes to the regulation of corrective reactions initiated by balance disturbances encountered during walking.