Which muscle action occurs when lengthening a muscle under tension?

The action of lengthening a muscle under tension is referred to as eccentric contraction. This occurs when a muscle generates force while being elongated, typically as it controls the descent of a load or a movement against gravity. For example, during a bicep curl, as the arm lowers the weight back to the starting position, the bicep muscle lengthens while still being engaged, demonstrating eccentric contraction.

This type of muscle action is crucial in various physical activities and plays a significant role in preventing injury, enhancing muscle strength, and improving performance. Eccentric contractions are especially important for activities such as descending stairs, slowing down after a sprint, or during the lowering phase of a squat. Understanding this action can help trainers design more effective strength training and rehabilitation programs that incorporate varied muscle actions to build overall muscle resilience.