Fig 1. Mechanisms to maintain balance during locomotion in the frontal plain.

Panel (A) shows the biomechanics of the upright body during locomotion under the simplifying inverted pendulum assumption. The horizontal CoM accelerates away from the CoP, with the magnitude of the acceleration proportional to the distance between the two. The lower panels illustrate how the CoP can be modified during walking. (B) At each new step, the lateral foot placement can be adjusted, shifting the CoP throughout the following stance phase. (C) During single stance, the CoP can be adjusted within the limits of the stance foot sole. (D) Foot placement changes are mainly accomplished by hip ab-/adduction of the swing leg, (E) lateral rolling of the stance foot by the ankle musculature.