What type of muscle action occurs when muscles shorten?

When muscles shorten during a contraction, the type of muscle action that is occurring is known as concentric contraction. In this action, the muscle generates force while simultaneously decreasing in length, allowing for movements like lifting weights or climbing.

For example, during a bicep curl, as you lift the weight towards your shoulder, your bicep muscles shorten, performing a concentric contraction. This is essential for various athletic movements and everyday activities.

In contrast, isometric contractions involve the muscle generating force without changing its length, which occurs when the muscle exerts force against an immovable object. Weakened muscle action is not a defined term in muscle physiology and does not describe a specific contraction type. Eccentric contractions occur when muscles lengthen under tension, typically when lowering a weight or controlling movement against gravity. Understanding these differences is crucial in biomechanics and training program design.