Define eccentric contraction.

Eccentric contraction is characterized by the muscle lengthening while generating force. This type of contraction occurs when the muscle is under tension while it is being elongated, typically when resisting or controlling the movement of an external force. For example, during the lowering phase of a bicep curl, the bicep muscle is actively lengthening while still exerting force to control the descent of the weight. This is significant in activities such as walking, running, and weightlifting, as eccentric contractions can contribute to muscle growth and strength due to the greater mechanical tension applied to the muscle fibers.

The other answers do not accurately describe eccentric contraction; one suggests that the muscle shortens, which describes concentric contraction, while another states that there is no movement, referring to isometric contraction. The statement regarding only fast-twitch fibers is misleading, as both slow-twitch and fast-twitch fibers can undergo eccentric contraction. Understanding these distinctions helps in the application of kinesiology principles in fields like rehabilitation and sports performance training.