Fig. 7. Hip joint moment, angle and power during single footfalls for three representative strides during a steady-speed run, a moderate acceleration and a high acceleration (mean acceleration during stance=0.13 m s^-2, 2.31 m s^-2, and 4.47 m s^-2 respectively). Angles and moments are measured as indicated in Fig. 1. The area under the positive power curve represents work done at the joint, while the area above the negative region of the power curve is work done on the joint.