Reactive stepping responses to novel slip-like gait perturbations in older adults with mild cognitive impairment: An experimental laboratory study

Older adults with mild cognitive impairment (OAwMCI) show reactive stepping deficits compared to cognitively intact older adults (CIOA) when unannounced perturbations occur. However, these findings were derived from stance perturbation paradigms, whereas most real-life falls occur while walking (e.g., slips). This study compared responses to a novel slip-like perturbation (backward loss of balance) during treadmill walking in OAwMCI vs. CIOA, including kinematic outcomes (margin of stability (MOS), center of mass position (COMx) and velocity (COMv), step length, trunk angle) and muscle synergy structures extracted from lower limb EMG data from 8 muscles (bilateral biceps femoris, vastus lateralis, medial gastrocnemius, tibialis anterior). There were no differences in pre-slip gait characteristics between groups (p > 0.05), although OAwMCI showed significantly lower MOS and more posterior COMx than CIOA at post-slip recovery touchdown (p < 0.05). Five clustered synergies were identified during reactive stepping, including both stance limb-dominant and stepping limb-dominant synergies. Three synergies were highly similar between groups (r > 0.966), while two synergies showed lower structural similarity (r < 0.768), and generally indicated greater intra-limb contribution (muscles on the same limb) in OAwMCI. These findings suggest that OAwMCI may experience impaired reactive stepping responses to slip-like perturbations during walking, which we postulate could be related to altered neuromuscular control (e.g., different muscle synergy structures) or sensorimotor processing/integration deficits, which are often reported in this population and could potentially impair perturbation perception.