What is the term for the shortening of a muscle?

The term for the shortening of a muscle is concentric contraction. During this type of contraction, the muscle generates enough force to overcome resistance, resulting in muscle fibers shortening as they contract. This action is commonly observed during activities such as lifting weights, where the muscle's flexion leads to movement toward the body's center.

In contrast, eccentric contraction occurs when a muscle lengthens while still under tension, typically when lowering a weight. Isometric contraction involves a muscle generating force without changing its length, meaning there is no movement despite the muscle being actively engaged. Co-contraction refers to the simultaneous activation of agonist and antagonist muscle groups to stabilize a joint, which does not specifically relate to muscle shortening. Therefore, concentric contraction is the precise term that describes the process of muscles shortening during movement.