Human resilience to forward falls: adaptation and transfer of stability control

Scoping fall resilience requires knowledge of factors enabling the neuromotor system to transfer stability control between different postural perturbations. This thesis addressed this objective in comprising three different studies on adults across the lifespan. The first study examined the intra- and inter-session reliability of recovery performance across 97 participants at several research centres using two different protocols of a clinical assessment method (lean-and-release task) simulating sudden anterior stability loss, i.e. gradual increase to maximal forward-lean angle vs. predefined lean angle. Independent of the protocol used and participants’ age, reliable assessment of common stability recovery performance parameters using the lean-and-release task could be confirmed. The second study used single exposures to both lean-and-release and a treadmill-based gait trip to investigate the association of recovery performance between unpractised perturbations. We revealed that recovery performance in one task could not significantly explain performance in the other task, indicating limited transfer of fall-resisting skills for anterior perturbations. The third study examined factors (particularly practising stability recovery responses with different perturbation magnitudes) that could elicit or limit transfer to unpractised perturbations. Participants walking on a treadmill were exposed to eight trip perturbations of either low or high magnitude or walked unperturbed (control group). To investigate transfer to unpractised anterior perturbations following walking tasks, all participants underwent a lean-and-release task and an overground trip. Adaptation in stability to repeated gait-perturbations did not lead to enhanced stability recovery in the lean-and-release task but did improve overground trip performance, independent of the practised perturbation magnitude. Lower limb joint angle differences between treadmill- and lean-and-release perturbations for the swing phase of recovery steps were more prolonged and greater as opposed to the comparison of the two gait perturbation tasks. In conclusion, the current work indicates that practising stability control enhances human resilience to unpractised perturbations which is not necessarily dependent on the perturbation magnitude but may partly be subject to similarity in motor response patterns between tasks.