Fig. 2. Joint kinematics. Thick curves are nine subject mean ankle, knee and hip joint kinematics for unpowered walking from the beginning of practice session 3 (black) and powered walking at the beginning of practice session 1 (light gray) and end of practice session 3 (dark gray). Thin curves are +1 s.d. and match colors for means. Curves are the stride average of left and right legs and are plotted from heel-strike (0%) to heel-strike (100%). Stance is 0% to 60% of the stride, swing 60% to 100%. For all joints, zero degrees is upright standing posture. Ankle plantarflexion, knee extension and hip extension are positive.