Which movement primarily reduces side-to-side COM displacement?

Which movement primarily reduces side-to-side COM displacement?

• A. Frontal plane hip rotation
• B. Sagittal plane knee flexion
• C. Transverse plane hip rotation
• D. Ankle dorsiflexion

Answer: (A)

Managing side-to-side motion of the body's center of mass relies primarily on movements that control the pelvis and hip in the frontal plane. When the hip moves in this plane—abduction and adduction—the pelvis and thigh can shift laterally to keep the center of mass over the base of support as weight transfers from one leg to the other. This frontal-plane hip action directly counteracts lateral sway, reducing mediolateral COM displacement. In contrast, knee flexion in the sagittal plane mainly affects forward progression and leg length during stepping, not side-to-side stability. Rotation in the transverse plane changes twisting of the hip and trunk but doesn’t directly minimize lateral COM excursions. Ankle dorsiflexion also operates mostly in the sagittal plane, influencing forward movement and foot clearance rather than mediolateral balance.

Managing side-to-side motion of the body's center of mass relies primarily on movements that control the pelvis and hip in the frontal plane. When the hip moves in this plane—abduction and adduction—the pelvis and thigh can shift laterally to keep the center of mass over the base of support as weight transfers from one leg to the other. This frontal-plane hip action directly counteracts lateral sway, reducing mediolateral COM displacement.

In contrast, knee flexion in the sagittal plane mainly affects forward progression and leg length during stepping, not side-to-side stability. Rotation in the transverse plane changes twisting of the hip and trunk but doesn’t directly minimize lateral COM excursions. Ankle dorsiflexion also operates mostly in the sagittal plane, influencing forward movement and foot clearance rather than mediolateral balance.