Proactive modifications to walking stability under the threat of large, anterior or posterior perturbations

Biomechanically, fall likelihood after a walking perturbation may be influenced by: (1) the pre-perturbation state of stability (i.e., "initial conditions") and (2) how well someone responds to a perturbation (i.e., "recovery skill"). Anteroposterior walking stability must be modifiable—ideally while preserving gait speed—to be a target for fall-prevention interventions. We investigated if neurotypical adults could proactively modulate the pre-perturbation walking state of stability represented by anteroposterior stability margins. Eleven neurotypical adults walked on a treadmill at three speeds with and without anterior or posterior perturbations. We measured the margin of stability anteriorly at mid-swing and posteriorly at foot strike for pre-perturbation left and right steps. A repeated-measures factorial ANOVA evaluated main effects and interactions of walking speed, perturbation type, and limb. With posterior perturbation threats, posterior margin of stability increased at foot strike (p < 0.01) compared to that with no perturbations. With anterior perturbation threats, anterior margin of stability decreased at mid-swing during stance on the dominant limb compared to the dominant limb with no perturbations (p < 0.01). With any perturbation threat, step lengths shortened (p < 0.01) and step rates increased (p < 0.01). At slow speeds with posterior perturbation threats, double-support time decreased (p = 0.04). Proactive modifications to stability margins are indeed possible in a neurotypical population within a given walking speed. Consequently, anteroposterior stability may be a feasible target for fall-prevention interventions by targeting decreased step lengths or increased step rates. Beneficial modifications appear to be dependent upon measure direction and gait phase.