Kinematic and motor coordination of the inner and outer limb in running while turning

Curved running presents specific mechanical demands on the musculoskeletal system and relies on a multi-level coordination of the lower limb to regulate efficient and precise movements. When a subject runs on a curve, the velocity of the body's centre of mass must be deflected laterally and the body must rotate along a vertical axis to match its orientation to the new direction of movement. This study observed the joint and neuromuscular coordination adjustments of the inner and outer limbs during curved running and its comparison to straight-line running. We supported the hypothesis that the inner and outer limbs would adopt distinct functional roles to accommodate lateral forces.

We recorded the ground reaction force, kinematic motion and muscular activity of eleven recreational male runners on two different radii of curvature at speeds ranging from 7 to 19 km h^-1. The joint coordination in frontal and sagittal planes, and muscular activity and spinal motoneuron output were analysed. Each lower limb played a distinct role in curved running, and coordination was limb specific with key traits separating either limb.

The inner limb primarily managed lateral redirection of the body, relying on increased joint compliance and enhanced muscular activation in the hip abductors to accommodate the greater lateral forces. In contrast, the outer limb contributed more to propulsion and stabilisation to drive forward motion.

This study's results provide insight into how humans modulate limb mechanics and coordination to maintain stability and performance in curved trajectories, with potential applications in sports and rehabilitation.