Which energy-saving strategy reduces side-to-side excursion of the COM?

Which energy-saving strategy reduces side-to-side excursion of the COM?

• A. Frontal plane hip rotation
• B. Sagittal plane ankle rotation
• C. Stance phase knee flexion
• D. Horizontal plane pelvic rotation

Answer: (A)

The main idea is how hip motion in the frontal plane can tame the sideways sway of the body's center of mass during walking. Frontal plane hip rotation (the thigh moving toward and away from midline) lets the leg swing under the body with less lateral movement of the trunk. By keeping the leg more aligned with the midline as weight shifts from one leg to the other, the center of mass travels a straighter, smaller side-to-side path, reducing the work needed to redirect momentum each step. That direct reduction in medio-lateral COM excursion is where the energy savings come from. Knee flexion during stance mainly affects shock absorption and forward progression rather than lateral sway. Ankle rotation in the sagittal plane influences rollover and propulsion, not side-to-side COM path. Pelvic rotation in the horizontal plane can aid overall progression, but it doesn’t reduce lateral COM excursion as directly as hip abduction/adduction in the frontal plane.

The main idea is how hip motion in the frontal plane can tame the sideways sway of the body's center of mass during walking. Frontal plane hip rotation (the thigh moving toward and away from midline) lets the leg swing under the body with less lateral movement of the trunk. By keeping the leg more aligned with the midline as weight shifts from one leg to the other, the center of mass travels a straighter, smaller side-to-side path, reducing the work needed to redirect momentum each step. That direct reduction in medio-lateral COM excursion is where the energy savings come from.

Knee flexion during stance mainly affects shock absorption and forward progression rather than lateral sway. Ankle rotation in the sagittal plane influences rollover and propulsion, not side-to-side COM path. Pelvic rotation in the horizontal plane can aid overall progression, but it doesn’t reduce lateral COM excursion as directly as hip abduction/adduction in the frontal plane.