What type of muscle contraction occurs when a muscle lengthens under tension?

The type of muscle contraction that occurs when a muscle lengthens under tension is known as eccentric contraction. During this type of contraction, the force exerted by the muscle is less than the external load, allowing the muscle fibers to elongate while still generating tension. This typically happens when a muscle is acting to control the descent of a load, such as when lowering a weight or slowly descending on a squat.

Eccentric contractions are crucial in various activities and can lead to muscle damage and soreness, often contributing to increased strength and muscle hypertrophy over time. Understanding this type of contraction is fundamental in training regimens that aim to improve both strength and endurance.