During loading response, the GRF falls where relative to the hip axis?

During loading response, the GRF falls where relative to the hip axis?

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

Answer: (A)

During loading response the location of the ground reaction force (GRF) relative to the hip joint center determines the external moment you see at the hip. When the bodyweight vector from the GRF passes in front of the hip joint center, it creates an external hip flexion moment. The hip extensors (like the gluteus maximus and hamstrings) then work to counteract that flexion and keep the pelvis and thigh stabilized as the leg accepts weight. So, the GRF being anterior to the hip axis means a flexion tendency at the hip during loading response, which is resisted by hip extensors to control forward progression and maintain stability. If the GRF were posterior to the axis, it would produce an extension moment, which is not the typical pattern emphasized in loading response. Medial or lateral positions relate to frontal-plane effects (abduction/adduction) rather than the sagittal-plane flexion/extension currently described.

During loading response the location of the ground reaction force (GRF) relative to the hip joint center determines the external moment you see at the hip. When the bodyweight vector from the GRF passes in front of the hip joint center, it creates an external hip flexion moment. The hip extensors (like the gluteus maximus and hamstrings) then work to counteract that flexion and keep the pelvis and thigh stabilized as the leg accepts weight.

So, the GRF being anterior to the hip axis means a flexion tendency at the hip during loading response, which is resisted by hip extensors to control forward progression and maintain stability. If the GRF were posterior to the axis, it would produce an extension moment, which is not the typical pattern emphasized in loading response. Medial or lateral positions relate to frontal-plane effects (abduction/adduction) rather than the sagittal-plane flexion/extension currently described.