Center-of-mass based foot placement in stumble recovery

Exploring how foot placement relates to center-of-mass kinematics after unexpected disturbances for healthy adults could improve our understanding of human balance as well as inform the design/control of assistive device interventions to reduce fall risk. Therefore, in this work a kinematic dataset of stumble recovery responses from seven healthy adults was analyzed to investigate the effects of stumble perturbations on COM state, and the COM state's relationship to various foot placement metrics. COM velocity excursion after trips was significantly higher than excursion for unperturbed swing phases, increasing linearly as the trip occurred later in swing phase. Step length/width and foot position at heel-strike after the trip both increased with COM velocity at heel-strike, though weaker fits for foot positions suggest priority to other strategies. Swing durations were substantially longer for tripped swing phases versus normal swing phases and increased with COM velocity. This is the first investigation of these relationships for stumble recovery, and their alignment (or lack thereof) with previous models provides insights into the control of balance for this common daily-life disturbance.