Adaptations in foot coordination and variability to walking speed

The aim of this study was to investigate how walking speed affects intersegmental foot coordination dynamics across the stance phase, highlighting the foot’s functional role in gait. Using vector coding, we analysed three segment couplings: transverse shank–frontal hindfoot, frontal hindfoot–frontal forefoot, and frontal forefoot–sagittal hallux. We assessed foot coordination dynamics by analysing the nature of coordination patterns and mean coordination variability across the stance phase, using discrete analyses and continuous statistical modelling via statistical non-parametric mapping (SnPM). Faster walking altered coordination patterns, increasing pronation during early stance and supination during late stance, reflecting greater arch collapse and subsequent arch elevation, ultimately increasing arch stiffness to meet higher propulsive demands. Coordination variability was higher in early and late stance and increased with speed, suggesting more active regulation of foot coordination during transitions involving foot contact and lift-off. SnPM revealed speed-related changes in shank–hindfoot coupling during double- and single limb support and from energy absorption to generation, in hindfoot–forefoot coupling during energy transitions, and in forefoot–hallux coupling during the stance-swing transition. These findings indicate that interactions between proximal and distal foot segments modulate stiffness throughout stance, which may support efficient foot energetics during locomotion.