During loading response, the ankle GRF falls relative to the ankle axis in which direction?

During loading response, the ankle GRF falls relative to the ankle axis in which direction?

• A. Posterior to the axis
• B. Anterior to the axis
• C. Superior to the axis
• D. Medial to the axis only

Answer: (A)

The key idea is how the ground reaction force (GRF) relates to the joint axis. In loading response, the line of action of the GRF passes behind the ankle joint axis (posterior to it). When a vertical force acts behind the axis of rotation, it tends to rotate the foot into plantarflexion about the ankle. So the external moment at the ankle during this phase is plantarflexion, which the body then modulates with the ankle muscles as the tibia advances over the foot.

The key idea is how the ground reaction force (GRF) relates to the joint axis. In loading response, the line of action of the GRF passes behind the ankle joint axis (posterior to it). When a vertical force acts behind the axis of rotation, it tends to rotate the foot into plantarflexion about the ankle. So the external moment at the ankle during this phase is plantarflexion, which the body then modulates with the ankle muscles as the tibia advances over the foot.