On the Basis for Stumble Recovery Strategy Selection in Healthy Adults

Abstract

Healthy adults employ one of three primary strategies to recover from stumble perturbations - elevating, lowering, or delayed lowering. The basis upon which each recovery strategy is selected is unknown. Though strategy selection is often associated with swing percentage at which the perturbation occurs, swing percentage does not reliably predict strategy selection; it is not a physical quantity; and it is not strictly a real-time measurement. The objective of this work is to better describe the basis of strategy selection in healthy individuals during stumbles, and in particular to identify a set of real-time measurable, physical quantities that better predict strategy selection, relative to swing percentage. To do this, data from a prior stumble experiment was reanalyzed. A set of biomechanical measurements at/after the perturbation were taken and considered in a 2-stage classification structure to find the set of features that best explained the strategy selection process. For Stage 1 (decision between initially elevating or lowering of the leg), the proposed model correctly predicted 99.0% of the strategies used, compared to 93.6% with swing percentage. For Stage 2 (decision between elevating or delayed lowering of the leg), the model correctly predicted 94.0% of the strategies used, compared to 85.6% with swing percentage. This model uses dynamic factors of the human body to predict strategy with substantially better accuracy than swing percentage, even in mid-swing, and at multiple speeds, giving potential insight into human physiology and informing the design of fall-prevention interventions.

Factors leading to falls in transfemoral prosthesis users: a case series of sound-side stumble recovery responses

“…Five of the six transfemoral prosthesis users fell at least once in this study, while none of the seven healthy control participants fell in [14,24]. These results substantiate the high fall prevalence relative to healthy adults reported in retrospective studies [1-4, 7, 41, 42], highlighting that stumbles to the sound limb should not be overlooked when considering interventions for fall prevention.…”

“…Finally, the recovery strategy used after each perturbation was reported as one of the three previously characterized recovery strategies from healthy adult stumble studies: elevating, lowering, or delayed lowering. Strategies were determined based on the trajectory of the swing foot after perturbation (as in [13,14,24]): in the elevating strategy, the foot lifts up and over the obstacle after contact with the obstacle; in the lowering strategy, the foot lowers to the ground behind the obstacle after contact with the obstacle; in the delayed lowering strategy, the foot initially elevates (i.e., shows upward motion) before elevation is abandoned and the foot subsequently lowers to the ground without clearing the obstacle. Refer to the legend of Fig.…”

“…Data from a previous healthy adult stumble study [14,24] were used for comparison to the responses of transfemoral prosthesis users. Seven healthy adults underwent a similar protocol using the same experimental apparatus, in which each participant experienced approximately 28 obstacle perturbations while walking at 1.1 m/s.…”

“…Although not exactly speed-matched with the experiments described here, these data nonetheless provide insights regarding which metrics correspond to successful recovery responses, and thus better illustrate prospective deficiencies in responses that result in a fall. Another experiment was also conducted in which a single healthy adult participant repeated the protocol at a walking speed of 0.8 m/s [24]. The healthy participants were wearing the same marker set, and motion capture and GRF data were processed identically to the transfemoral prosthesis user dataset.…”

“…For healthy adults, such responses have been found to differ as a function of various factors, including (1) swing phase at which the perturbation occurs and (2) age of the participants. Regarding (1), recovery strategy selected depends on the dynamic state of the human body at the perturbation [24], factors that vary depending on when in swing phase the perturbation occurs. Regarding (2), older adults fall more often, which has been attributed to delayed and decreased muscle activation in the response [16,19,25,26].…”