Which type of muscular contraction occurs when the muscle shortens?

The type of muscular contraction that occurs when the muscle shortens is called concentric contraction. During a concentric contraction, the muscle generates force while it is actively shortening; this typically happens when lifting a weight or moving against resistance.

For example, when performing a bicep curl, as you lift the weight towards your shoulder, your biceps are undergoing concentric contraction. This shortening allows for movement and is essential in many exercises that focus on building strength and power.

In contrast, the other types of muscular contractions mentioned do not involve shortening the muscle. Isometric contractions occur when the muscle generates force without changing length, often while holding a position like a plank. Eccentric contractions happen when the muscle lengthens while under tension, such as when you lower the weight back down in a bicep curl. Isotonic contractions refer to muscle contractions with a change in length, but this term collectively covers both concentric and eccentric contractions, making it less specific than simply saying concentric for when a muscle shortens.