Whole-body kinematic adaptations to running on an unstable, irregular, and compliant surface.

The goal of this study was to investigate whole-body kinematic adaptations when running on an unstable, irregular, and compliant surface in comparison to running on asphalt. We hypothesised that the gait pattern (H1) and its stride-to-stride variability (H2) would be affected by the unstable surface but that variability related to some movement features would be reduced over multiple testing days indicative of gait optimisation (H3). Fifteen runners ran on a woodchip and asphalt track on five testing days while their whole-body movements were captured using inertial motion capture and examined using joint angle and principal component analysis. Joint angles and stride-to-stride variability in eight principal running movements were subjected to surface by day analyses of variance. The woodchip track compared to asphalt resulted in (H1) a more crouched gait pattern including more leg flexion and forward trunk lean and (H2) higher stride-to-stride variability in most investigated principal running movements. However, (H3) stride-to-stride variability did not systematically change over testing days. Running on an unstable, irregular, and more compliant surface leads to the adoption a gait pattern and control strategy that are more robust against disturbances caused by the surface but may pose certain risks for overuse injury in trail runners.