Which type of muscle contraction involves lengthening of the muscle?

The type of muscle contraction that involves the lengthening of the muscle is eccentric contraction. During an eccentric contraction, the muscle produces force while it is being elongated, typically occurring when the muscle is under tension while gradually lengthening against a load. This can be observed in activities such as lowering a weight in a controlled manner or descending stairs, where the muscle must control the motion while it lengthens.

In contrast, isometric contractions occur when the muscle generates force without changing its length, such as holding a position against a stationary object. Concentric contractions involve the muscle shortening while generating force, as seen when lifting a weight. Isokinetic contractions happen at a constant speed throughout the range of motion but can involve both lengthening and shortening phases depending on the movement.