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.