Influence of handrail height and fall direction on center of mass control and the physical demands of reach-to-grasp balance recovery reactions

The ability to maintain and recover center of mass (COM) and trunk control after a destabilization is critical for avoiding falls and fall-related injuries. Handrails can significantly enhance a person's ability to recover from large destabilizations, by enabling the person to grasp and apply high forces to the rail to stabilize their COM. However, the influence of handrail height and falling direction on COM control and the demands of grasping are unknown. We investigated the effect of handrail height (34, 38, 42 in.) and fall direction (forward, backward) on COM and trunk control, and the corresponding physical demands of reach-to-grasp balance reactions. Thirteen young adults were destabilized with platform perturbations, and reached to grasp a nearby handrail to recover balance without stepping. COM kinematics and applied handrail forces were collected. COM control was evaluated in terms of: (1) COM range and peak displacement, velocity and momentum in all Cartesian axes; and (2) trunk angular displacement, velocity and momentum in the roll and pitch axes. The physical demands of grasping were estimated via resultant handrail impulse. Compared to forward-directed falling, backward-directed falling was generally associated with greater peak COM and trunk angular displacement, velocity and momentum, along with greater handrail impulse. Higher handrails generally resulted in reduced peak COM and trunk angular displacement, velocity and momentum, as well as reduced handrail impulse. These results suggest that higher handrails may provide a stability advantage within the range of handrail heights tested, with better COM control achieved with lower physical demands of grasping.