During terminal stance and pre-swing, the GRF is positioned where relative to the knee axis?

During terminal stance and pre-swing, the GRF is positioned where relative to the knee axis?

• A. Posterior to the axis
• B. Anterior to the axis
• C. Directly through the hip
• D. Medial only

Answer: (A)

During late stance, as the body moves toward toe-off, the line of action of the ground reaction force moves behind the knee joint axis. When the GRF is posterior to the knee axis, the moment it creates tends to extend the knee, aiding propulsion and initiating toe-off. That posterior position best explains why the knee experiences an external extension moment in terminal stance and pre-swing. If the GRF were anterior to the knee axis, it would produce an external knee flexion moment (opposing extension). If the force acted directly through the knee axis, the external moment would be near zero. The notion of being “medial only” isn’t a typical descriptor for the knee’s sagittal-plane moment in this phase.

During late stance, as the body moves toward toe-off, the line of action of the ground reaction force moves behind the knee joint axis. When the GRF is posterior to the knee axis, the moment it creates tends to extend the knee, aiding propulsion and initiating toe-off. That posterior position best explains why the knee experiences an external extension moment in terminal stance and pre-swing.

If the GRF were anterior to the knee axis, it would produce an external knee flexion moment (opposing extension). If the force acted directly through the knee axis, the external moment would be near zero. The notion of being “medial only” isn’t a typical descriptor for the knee’s sagittal-plane moment in this phase.