Fig. 5. The moment arm of the ground reaction force (R; Fig. 1) averaged over the step did not change with acceleration at the ankle or tarsometatarsal–phalangeal (TMP) joint. Hip moment arm increased with acceleration (y=0.0061x+0.069, r²=0.23, P<0.001). Mean moment arms during knee extension (green) and knee flexion (blue) were measured separately. Only the mean flexion moment arm at the knee changed significantly with acceleration. Linear regression for the knee flexion moment arm was y=–0.0070x–0.029, r²=0.27, P<0.05.