Which muscle weakness is most associated with trunk lateral bend during stance?

• A. Weak extensors
• B. Weak abductors
• C. Weak adductors
• D. Weak flexors

Answer: (B)

The key idea is how the pelvis is kept level during single-leg stance in gait. The hip abductors on the stance leg (gluteus medius and minimus) contract to prevent the pelvis from dropping toward the swing leg. When these muscles are weak, the pelvis sags on the side opposite the stance leg. To compensate and keep the upper body balanced over the stance leg, the trunk shifts laterally toward the stance side. That trunk lateral bend during stance is a classic sign of hip abductor weakness.

Extensors mainly stabilize the trunk in the sagittal plane; weakness there tends to cause forward sag or difficulty maintaining an upright posture rather than a lateral bend. Adductors and flexors influence leg alignment and movement more in the frontal or sagittal planes of the thigh and knee, not the frontal-plane control of the pelvis during stance. So the lateral-trunk compensation points most directly to weak abductors.