Abstract
Sensory-motor deficits associated with below-knee amputation impair reactions to external perturbations. As such, below-knee prosthesis users rely on proactive control strategies to maintain locomotor stability. However, there are trade-offs (metabolic, comfort, etc.) associated with proactive strategies. We hypothesize that because proactive control strategies are costly, prosthesis users and non-impaired participants will use a priori knowledge (timing, direction) of an impending lateral perturbation to make specific gait adaptations only when the timing of the perturbation is known and the adaptation can be temporally-limited. This hypothesis was partially supported. When the perturbation timing was predictable, only prosthesis users, and only on their impaired side, increased their lateral margin of stability during the steps immediately preceding the perturbation when perturbation direction was either unknown or known to be directed towards their impaired side. This strategy should reduce the likelihood of requiring a corrective step to maintain stability. However, neither group exhibited substantial proactive adaptations compared to baseline walking when perturbation timing was unpredictable, independent of perturbation direction knowledge. The absence of further proactive stabilization behaviors observed in prosthesis users in anticipation of a certain but temporally unpredictable perturbation may be partially responsible for impaired balance control.
Highlights
BKPUs appear to make only small anticipatory gait adaptations when repeatedly exposed to discrete but temporally-unpredictable lateral perturbations[22]
When BKPUs anticipate a temporally-unpredictable perturbation with a known recoverable magnitude as employed in the study by Sturdy et al.[22], choosing to maintain their preferred gait pattern would help avoid those costs associated with further proactive adaptations to increase stability
The purpose of this study was to quantify the effects of a priori spatiotemporal information of a discrete, lateral perturbation on proactive locomotor strategies employed by non-impaired controls and BKPUs walking with passive prosthetic components
Summary
BKPUs appear to make only small anticipatory gait adaptations when repeatedly exposed to discrete but temporally-unpredictable lateral perturbations[22]. When BKPUs anticipate a temporally-unpredictable perturbation with a known recoverable magnitude (i.e., below the threshold which would result in a fall) as employed in the study by Sturdy et al.[22], choosing to maintain their preferred (already cautious) gait pattern would help avoid those costs associated with further proactive adaptations to increase stability. Knowing the timing of a perturbation during continuous walking would allow proactive strategies to be temporally-restricted to only the steps immediately preceding the perturbation rather than incurring an ongoing cost every step Knowledge of both timing and direction could encourage even more focused adaptions to prepare for an impending perturbation. The purpose of this study was to quantify the effects of a priori spatiotemporal information of a discrete, lateral perturbation on proactive locomotor strategies employed by non-impaired controls and BKPUs walking with passive prosthetic components (i.e., no active joint control). Our results from studying the effects of contextual perturbation information on proactive strategies of BKPUs and their differences compared to non-impaired individuals would enhance understanding of the mechanisms used by BKPUs to maintain locomotor stability
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