Which contraction lengthens under opposing force?

• A. Isotonic contraction
• B. Eccentric
• C. Concentric
• D. Isometric

Answer: (B)

The scenario describes eccentric contraction. In this type, the muscle produces force while it lengthens, usually when an external load causes the limb to move downward or slow a descent. For example, lowering a weight during a bicep curl—the biceps lengthen as they resist the force of gravity. This is why it’s the best answer: the defining feature is lengthening under an opposing force.

Concentric contractions shorten the muscle as it works against a load, isometric contractions keep the muscle length the same under load, and isotonic refers to contractions with a constant external resistance that can involve both shortening and lengthening phases but doesn’t specify lengthening under opposing force by itself.