Light touch and center of mass stability during treadmill locomotion

Purpose: To study the contributions of light fingertip touch on an earth-referenced object to body stability during treadmill locomotion. Method: Twenty young healthy adults were tested in two blocks of five testing conditions while walking on the treadmill at 3 km/h. In each condition, subjects were tested with eyes open (EO) and with eyes closed (EC). In each block, four separate conditions of heavy (H) or light (L) touch to either a left or to a right force sensor mounted on the respective side rail, as well as one condition of no touch (N), were randomly applied. The 3D positions of the center of mass (COM) and the midpoint of the posterior aspect of each leg were monitored via a kinematic ultrasonic system, while the anterior–posterior (AP) acceleration of the COM was measured with a uniaxial linear accelerometer. Results: Light touch had a similar stabilizing effect as vision and as heavy touch on COM sway. Thus, COM sway and AP acceleration were comparable in conditions of eyes open and eyes closed as long as touch was applied. Conversely, without vision and touch, subjects drifted backwards, with complete disruption of the coordinated stepping pattern. Conclusions: Somatosensory fingertip input from an external reference provides spatial orientation, which, similar to vision, enables the sustaining of body stability during treadmill walking.