What happens to muscles during eccentric contraction?

During eccentric contraction, muscles lengthen while actively resisting an external force. This type of contraction occurs when a muscle is under load while it is being elongated. For example, when lowering a heavy object, the muscles that control this movement—such as the biceps during the downward motion of a bicep curl—are engaged but still lengthen as the object descends.

This mechanism is fundamental for activities that involve deceleration and controlled movements, allowing for smooth transitions rather than abrupt stops or breaks. Eccentric contractions are particularly important for maintaining joint stability and can lead to increased muscle strength over time due to the high levels of tension that can be generated even at a lengthened state.