Which type of contraction occurs when lifting a weight and the muscle is shortening?

A concentric contraction occurs when the muscle shortens while generating force, such as when lifting a weight. This type of contraction is fundamental in movements where the muscle is actively working against resistance to cause movement. For instance, when performing a bicep curl, as the weight is lifted towards the shoulder, the bicep muscle shortens to produce the lift, demonstrating a concentric contraction.

In contrast, eccentric contractions involve the muscle lengthening while still under tension, such as when lowering a weight. Static contractions maintain muscle length without the muscle changing size, often experienced when holding a weight in a fixed position. Plyometric contractions are quick stretches followed by contractions and typically involve jumping or explosive movements. Each term defines a specific type of muscle action, with concentric being characterized by shortening under load, making it the correct choice for this question.