Recovery strategies during trip-like support surface perturbations while walking in older adults with mild cognitive impairment.

Older adults with mild cognitive impairment (OAwMCI) fall 2 × more than cognitively intact older adults (CIOA), possibly due to impaired reactive stepping. However, most studies in OAwMCI have focused on slip-like perturbations (backward loss of balance), rather than trip-like perturbations (forward loss of balance). This study examined reactive stepping strategies following a novel support surface perturbation during treadmill walking, and compared fall rate, margin of stability (MOS), step length, and trunk angle between OAwMCI and CIOA during unperturbed walking (i.e., pre-trip) and recovery stepping (i.e., post-trip). As an exploratory analysis, muscle synergies were also extracted from bilateral lower limb EMG data from perturbation onset to recovery touchdown. After trip onset, most participants took a lowering-like step with the swing limb, followed by a forward recovery step with the contralateral (43% CIOA, 58% OAwMCI) or ipsilateral limb (57% CIOA, 42% OAwMCI). Pre-trip outcomes were similar between groups (p > 0.05), and there was no significant difference in fall rate between OAwMCI (92%) and CIOA (78%). However, OAwMCI showed higher MOS at recovery touchdown compared to CIOA (p = 0.011) regardless of the limb used for reactive stepping. During both stepping strategies, 2-3 muscle synergies showed low structural similarity between OAwMCI and CIOA. These results indicate that reactive stepping responses in OAwMCI may be less effective for restoring COM stability after trip-like perturbations, potentially due to deficits in sensorimotor integration or selection/execution of motor commands. Reactive balance deficits could potentially interfere with reactive stepping in multiple directions and contribute to increased fall risk.