Fig. 2. Joint kinematics. The thick lines show the mean ankle (left column), knee (middle column) and hip (right column) joint angles (degrees) over the stride from heel strike (0%) to heel strike (100%) of nine subjects. Data are averages of left and right legs. Each row is walking data for a single speed/step length (0.8 L^* at top to 1.4 L^* at bottom). In each subplot, curves are for unpowered (black circles), and powered walking (gray circles) and thin lines are +1 s.d. Stance is 0–60% of the stride, swing 60–100%. Ankle joint plantarflexion, knee joint extension and hip joint extension are all positive. For all joints, 0 deg. is upright standing posture.