Preserved coordination structure and distance-related changes in task-variable stabilization: A PCA-UCM analysis of inter-joint synergies during a 10-km run.

BACKGROUND

Endurance running performance depends on how multi-joint synergies distribute control across propulsion, absorption, and stability, yet process-level evidence on the along-distance evolution of inter-joint coordination during long runs remains scarce.

METHODS

Fifteen trained runners completed a constant-speed 10-km treadmill run. PCA was used to extract inter-joint synergy features across the 1-10 km segments. UCM was then applied to relate synergy variability to fluctuations in COM fore-aft (AP) velocity.

RESULTS

The first three principal components consistently explained the majority of variance: PC1 (ankle-driven distal propulsion), PC2 (hip-dominant proximal stabilization/propulsion), and PC3 (ankle-knee cross-plane coupling). With increasing distance, the contribution of distal rotational DOFs (e.g., left-ankle internal/external rotation) decreased, whereas hip loadings remained stable. UCM showed VUCM ≈ 0.180-0.190 (stable), VORT rising from 0.013 at 1 km to 0.029 at 10 km, and a large but slightly declining synergy index ΔV (0.75-0.88) as load accumulated; a VORT peak / ΔV trough emerged around 6 km.

CONCLUSIONS

Across the 10-km run, coordination structure remained largely preserved, whereas VORT increased and ΔV decreased, indicating a modest distance-related increase in task-variable-affecting variability and a reduction in UCM-based synergy strength.