Figure 1.

Trailing-limb push-off affects both sagittal plane and frontal plane dynamics. Ankle push-off generates a force (F) commonly understood to affect motions in the sagittal plane (left) but which also affects motions in the frontal plane (right). In general, the combination of push-off and gravity, with finite mediolateral displacement between the center of pressure and the center of mass (r) results in a mediolateral force at the foot (F _y), thereby contributing to mediolateral acceleration of the body (a _y). Neglecting rotational inertia about the center of mass, the effect on lateral acceleration is proportional to push-off force as $\Delta {\mathit{\text{a}}}_{\mathit{\text{y}}}=\frac{1}{m}·\frac{\mathit{\text{r}}}{L}·\Delta \mathit{\text{F}}$, where L is leg length.