Which contraction lengthens the muscle under tension?

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

Answer: (C)

The key idea is how muscles behave as they generate force while changing length. When a muscle produces force but lengthens as it does so, that’s an eccentric contraction. This happens, for example, when you slowly lower a weight or brake your body as you descend in a squat—the muscle is under tension and lengthening at the same time. By contrast, a concentric contraction shortens the muscle as it contracts (like lifting a weight), an isometric contraction keeps the length the same while contracting (holding a position), and tonic contraction refers to a constant, baseline level of muscle tone rather than a movement type. So the correct concept is eccentric contraction, where the muscle lengthens under tension.