Effects of unexpected underfoot perturbations during turning on measures of mediolateral stability and corresponding recovery strategies.

Humans regularly walk across uneven terrain, which demands reactive control strategies to maintain forward progress and stability. While reactive control during walking has been well described during straight gait, it is unclear how reactive control differs during turning gait. Because turning is asymmetrical, perturbations to the inside and outside limbs may elicit different reactive adjustments. This study investigates how unexpected underfoot perturbations alter stability measures during turning and how individuals alter their foot placement to maintain stability after such perturbations. Seven healthy adults completed walking trials around a circular track while wearing mechanized shoes that pseudo-randomly delivered underfoot perturbations to either the inside or outside limb. We calculated mediolateral margin of stability corrected for centripetal acceleration (ML MoSC), step width and step length from kinematic data. Linear mixed effects models compared the effects of perturbation type (inversion versus eversion) and perturbed limb (inside versus outside) for each outcome measure. ML MoSC was affected by both perturbation type and perturbed limb, with larger changes observed during eversion and outside limb perturbations. Changes to step width and step time during two recovery steps after each perturbation were primarily influenced by the perturbed limb - outside limb perturbations elicited consistent changes during two recovery steps compared with one altered step after inside limb perturbations. Perturbations to the outside limb during turning disrupted gait longer than perturbations to the inside limb. This difference across perturbed limb may indicate that outside steps are more important than inside ones for maintaining and recovering stability during turning.