Which contraction involves the muscle lengthening under tension?

• A. eccentric
• B. concentric
• C. isometric
• D. isotonic

Answer: (A)

Lengthening under tension describes an eccentric contraction. In this type, the muscle remains active and produces force while it lengthens, typically controlling the lowering or deceleration of a movement. This happens when the external resistance is greater than the muscle’s shortening capacity, so the muscle lengthens as it tethers the movement rather than lifting it. Think of lowering a dumbbell in a bicep curl or the down phase of a squat—the muscle is working and generating force, but it’s lengthening rather than shortening.

Concentric contractions shorten the muscle while producing force, so that wouldn’t fit. Isometric contractions keep the muscle the same length while generating force, which also isn’t it. Isotonic contractions involve a change in length under a constant load and can include both shortening and lengthening phases, but the key feature asked about is the lengthening while under tension—that’s eccentric.