Fig 9. Effect of weakened dorsiflexors and hip abductors on motion tracking.

Left: Weakening the ankle dorsiflexors caused ankle plantarflexion to increase during early stance and swing (orange) compared to the experimental ankle angle (gray) and the normal tracking solution (black curves, white skeleton). The tibialis anterior force is normalized by the normal max isometric force of the muscle, F_iso. Right: Weakening the hip abductors resulted in a reduced hip adduction angle (green) during stance compared to the experimental hip adduction angle (gray) and the normal tracking solution (black). As shown in the skeleton graphic, increased trunk sway was observed (green) compared to the normal tracking solution (white). The force in the gluteus medius, a primary hip abductor, was nearly reduced to zero across the gait cycle.