Modulation of muscle coordination complexity during goal-directed lateral stepping is associated with vulnerability...

Falls in community-dwelling older adults frequently occur while walking, requiring rapid regulation of whole-body biomechanics. Age-related reductions have been observed in the modulation of muscle coordination complexity in balance-challenging walking tasks. It is not known if such reductions are relevant to reactive responses to unexpected disturbances. This study aimed to determine whether modulation of muscle coordination complexity from habitual walking to goal-directed lateral stepping (GDLS) is associated with vulnerability to walking balance perturbations in older adults.

Twenty-five older adults participated in the study. Muscle coordination complexity was quantified as variability not accounted for by one motor module (VNAF1). Modulation was defined as VNAF1 during goal-directed lateral stepping minus VNAF1 during habitual walking. Vulnerability to perturbations was assessed using peak-to-peak whole-body angular momentum (WBAM) in response to lateral waist-pulls and treadmill-induced slips. Linear mixed regression models tested associations between complexity measures and perturbation-induced WBAM.

Modulation of muscle coordination complexity was significantly associated with perturbation-induced WBAM. Greater reductions in complexity during goal-directed lateral stepping were associated with reduced frontal-plane WBAM in response to lateral waist-pulls (i.e., less vulnerability). In contrast, greater reductions in complexity during goal-directed lateral stepping were associated with increased sagittal-plane WBAM in response to treadmill-induced slips. Muscle coordination complexity during habitual walking was not significantly associated with perturbation responses.

Modulation of muscle coordination complexity during balance-challenging walking tasks was associated with reactive balance responses in older adults, suggesting that modulation capacity may reflect neuromuscular control strategies relevant to both voluntary and reactive balance control.