Which type of muscle contraction involves muscle shortening?

Muscle contraction that involves muscle shortening is categorized as concentric contraction. During a concentric contraction, the muscle generates force while shortening, typically occurring when the muscle's fibers contract and pull on the bones to create movement. This type of contraction is often seen when lifting weights or performing activities where the muscle must overcome resistance, such as during a bicep curl when the elbow flexes.

In contrast, isometric contractions refer to muscle activation where the muscle length remains constant while generating force, as seen when holding a weight in a fixed position. Eccentric contractions involve the muscle lengthening while still generating force, which often occurs when lowering weights or controlling movements against gravity. Isokinetic contractions involve controlling the speed of contraction through a full range of motion against a variable resistance, and are typically utilized in rehabilitation settings.

Therefore, the distinct nature of concentric contraction—where the muscle actively shortens to produce movement—clearly identifies it as the correct option in this context.