Energy analysis of human stumbling: the limitations of recovery.

This study has analyzed the segmental energy changes in the recovery from a stumble induced during walking on a treadmill. Three strategies emerged according to the behavior of the perturbed limb, elevating, lowering, and delayed lowering. These three strategies showed different changes in the segmental energy with respect to normal gait. In the elevating strategy, the energy loss induced by the stumble was restored during the perturbed step and reached normal levels during the recovery step. The largest energy changes occurred in the lowering and delayed lowering strategies during the double stance (DS) phase. Moreover, in some of these trials there was energy absorption during the double stance phase for several strides after the perturbation. The most challenging perturbations had longer duration or occurred at mid-swing, triggering delayed lowering or lowering strategies, because more strides and larger energy changes were needed to recover, suggesting a trade-off between stability and energy efficiency.