Differential temporal responses of heel strike and toe off during split-belt locomotor adaptation

Human walking must maintain temporal coordination while adapting to perturbations. However, it remains unclear whether different gait events show similar or distinct temporal responses during adaptive walking. Using split-belt treadmill walking as a model of asymmetric temporal perturbation, we examined inter-event timing variability for heel strike (HS) and toe off (TO) in healthy young adult males.

Variability was quantified as the coefficient of variation (CV) of inter-event intervals during baseline walking, early adaptation, and late adaptation. To assess perturbation-related temporal responses, we also calculated baseline-referenced changes in variability (ΔCV) and their magnitude (|ΔCV|).

HS exhibited higher absolute timing variability across walking phases and larger baseline-referenced changes during split-belt walking. In contrast, TO showed comparatively lower variability and smaller deviations from baseline in the present analysis. Double-support time symmetry was also altered during early adaptation and partially recovered later, indicating concurrent reorganization of whole-gait temporal coordination.

These findings suggest that gait events do not contribute uniformly to temporal adjustment during split-belt walking. Event-specific analysis of baseline-referenced variability may therefore provide a useful perspective for describing temporal responses to locomotor perturbation.