Which type of muscle contraction is characterized by the muscle lengthening under tension?

The correct choice is eccentric contraction, which is specifically defined as a type of muscle contraction where the muscle lengthens while under tension. This occurs, for example, when a muscle is working to control movement against the force of gravity, such as lowering a weight. During this process, the muscle fibers are activated to maintain tension while essentially elongating, which helps to control the descent smoothly and maintain stability.

Eccentric contractions are important for various physical activities, including running and jumping, where muscles are required to lengthen under load to facilitate controlled movement and prevent injury. They also play a critical role in muscle hypertrophy and strength training, as eccentric loading is known to create more micro-tears in the muscle fibers, leading to greater repair and adaptation over time.

In contrast, isometric contractions occur when the muscle generates force without changing its length, concentric contractions happen when the muscle shortens while generating force, and dynamic contractions can refer to both concentric and eccentric actions but do not specifically describe the lengthening aspect.