Which type of contraction occurs when a muscle lengthens while under tension?

Eccentric contraction is the type of contraction that occurs when a muscle lengthens while still generating tension. This type of contraction typically happens when a muscle is acting against a load that is greater than the force the muscle generates. During eccentric contractions, the muscle fibers elongate as the muscle exerts force. This mechanism is crucial in various activities such as slowly lowering a weight, running downhill, or descending stairs, where the muscle works to control the movement and decelerate the load. Eccentric contractions are essential for muscle development and injury prevention as they promote muscle strength and stability.

On the other hand, concentric contraction involves a muscle shortening while generating tension, isometric contraction involves a muscle generating tension without changing its length, and isokinetic contraction describes a scenario where the muscle contracts at a constant speed. These other types of contractions play important roles in muscle movement and function, but they do not involve the lengthening of the muscle under tension like eccentric contraction does.