Stance phase knee flexion reduces upward COM displacement by doing what to the functional length of the leg?

Stance phase knee flexion reduces upward COM displacement by doing what to the functional length of the leg?

• A. Lengthening it maximally
• B. Moving it laterally only
• C. Shortening it slightly
• D. Fixing it at full extension

Answer: (C)

Knee flexion during stance shortens the leg’s functional length, which lowers the body’s center of mass and reduces how much it rises as you move over the stance limb. A shorter leg acts like a lower “shaft” for the body's weight, dampening vertical motion. If the leg were lengthened or kept fully extended, the limb would project further vertically and allow a larger upward displacement of the center of mass. Lateral movement doesn’t meaningfully change vertical length, so it wouldn’t achieve the same reduction. Shortening it slightly best explains the reduced upward COM displacement.

Knee flexion during stance shortens the leg’s functional length, which lowers the body’s center of mass and reduces how much it rises as you move over the stance limb. A shorter leg acts like a lower “shaft” for the body's weight, dampening vertical motion. If the leg were lengthened or kept fully extended, the limb would project further vertically and allow a larger upward displacement of the center of mass. Lateral movement doesn’t meaningfully change vertical length, so it wouldn’t achieve the same reduction. Shortening it slightly best explains the reduced upward COM displacement.