The effect of running speed on lower limb coordination variability and movement regularity during barefoot running in overweight adults.

Whether the elevated injury risk in overweight runners reflects excessively regular, over-constrained coordination or insufficiently stable coordination remains unclear. It was hypothesised that body mass and running speed interact to alter lower limb coordination during barefoot running. Overweight (n = 18) and normoweight (n = 14) adults ran barefoot at 6, 8, 10, and 12 km/h. Stance-phase mechanics were analysed using spatial coordination variability (CV), temporal approximate entropy (ApEn), and peak plantar pressure. A distinct speed-dependent transition was observed in the overweight cohort. During propulsive phases at moderate speeds, overweight runners exhibited lower sagittal plane CV and more regular movement patterns (lower ApEn at 8 km/h; p < 0.05). Conversely, at higher speeds, this pattern reversed: overweight individuals demonstrated significantly greater thigh-shank CV during early stance at 12 km/h (p = 0.008) and higher ApEn across multiple joints at 10 km/h, including knee abduction/adduction (p = 0.007). Mechanically, the overweight group exhibited consistently higher heel pressures (35.21 vs. 27.40 N/cm2; p = 0.014) and a larger speed-related increase in forefoot pressure (Group × Speed interaction: p = 0.005). These findings indicate that excess body mass is associated with a speed-dependent shift from more constrained coordination and greater temporal regularity at moderate speeds towards more variable and less regular coordination at higher speeds. Faster running speeds may therefore impose greater coordinative demands on overweight runners, and the underlying mechanisms warrant further investigation.