External torques during gait are generated by which mechanism?

External torques during gait are generated by which mechanism?

• A. Air resistance
• B. Only voluntary muscle contraction
• C. Ground reaction forces applied under the foot
• D. Only passive ligaments

Answer: (C)

External torques during gait come from forces outside the body acting on it, mainly the ground reaction forces at the foot–ground contact. When you push against the ground, the ground pushes back with a reaction force. Because this force often doesn’t line up with a joint’s center, it creates a moment arm that produces a rotational effect about the joint—an external torque. Air resistance at walking speeds is negligible, and voluntary muscle contraction generates internal torques, not external ones. Passive ligaments merely resist motion and help stabilize joints; they don’t create external torques. So the external torque most clearly comes from ground reaction forces under the foot.

External torques during gait come from forces outside the body acting on it, mainly the ground reaction forces at the foot–ground contact. When you push against the ground, the ground pushes back with a reaction force. Because this force often doesn’t line up with a joint’s center, it creates a moment arm that produces a rotational effect about the joint—an external torque. Air resistance at walking speeds is negligible, and voluntary muscle contraction generates internal torques, not external ones. Passive ligaments merely resist motion and help stabilize joints; they don’t create external torques. So the external torque most clearly comes from ground reaction forces under the foot.