Figure 2. Analysis of the effect of stepping on an inclined surface.

Grand mean ensemble averages of 18 able-bodied subjects' ankle dorsiflexion, knee flexion, Achilles' tendon force (ATF) estimate, normalized gastrocnemius medialis (GM) muscle–tendon length and GM muscle activity are presented for level, +3 deg and −3 deg inclination of the platform (thick, dashed, and dotted, respectively). The analysis window for the kinematics, force and EMG recordings is represented by the shaded areas (15–60% of stance). Stepping on the inclined surface shifts the ankle rotation at foot touch down. This has an effect on the muscle–tendon length throughout the step, illustrated here for GM. ATF estimates and muscle activity also vary concomitantly with the inclination of the platform.