What does the term "eccentric" describe in muscle actions?

The term "eccentric" specifically refers to a type of muscle contraction where the muscle lengthens while still generating force. This occurs when a muscle is under tension but is being elongated, typically while resisting an external load or force. For example, during activities like lowering a weight or controlling descent during a squat, the muscles involved are actively engaging in an eccentric contraction as they control the movement and resist the force of gravity.

Eccentric contractions are crucial for activities like braking movements and decelerating the body during physical tasks. This contrasts with other types of contractions such as concentric, where the muscle shortens, and isometric, where the muscle length does not change, both of which describe different states of muscle action. Understanding the nature of these contractions is essential for developing effective training protocols that target muscle strength and control.