Weak hip extensors may cause which trunk posture after initial contact?

Weak hip extensors may cause which trunk posture after initial contact?

• A. Anterior trunk lean
• B. Posterior trunk lean
• C. Pelvic rotation
• D. Increased knee flexion

Answer: (B)

When the leg is in early stance, gravity creates a flexion moment at the hip that the hip extensors must counteract to keep the trunk upright. If these extensors are weak, a backward (posterior) lean of the trunk shifts the body's center of mass behind the hip joint, so gravity provides an external extension moment at the hip. This reduces the demand on the weak hip extensors and helps maintain stance stability after initial contact. That compensatory posterior trunk lean best explains the postural change seen with hip extensor weakness.

When the leg is in early stance, gravity creates a flexion moment at the hip that the hip extensors must counteract to keep the trunk upright. If these extensors are weak, a backward (posterior) lean of the trunk shifts the body's center of mass behind the hip joint, so gravity provides an external extension moment at the hip. This reduces the demand on the weak hip extensors and helps maintain stance stability after initial contact. That compensatory posterior trunk lean best explains the postural change seen with hip extensor weakness.