Which type of contraction involves the muscle lengthening while still producing tension?

Eccentric contraction is characterized by the muscle lengthening while still generating tension. This type of contraction typically occurs when a muscle is actively controlled while it is being stretched. For instance, when lowering a weight during a bicep curl, the bicep muscle elongates as it gradually releases the hold on the weight, while still engaging and maintaining tension. This mechanism plays a crucial role in controlling movement and stabilizing the joints.

Unlike isometric contractions, where the muscle generates force without changing its length, and concentric contractions, where the muscle shortens as it contracts, eccentric contractions specifically focus on lengthening under tension. Isokinetic contractions involve muscle contractions that occur at a constant speed, usually with specialized equipment, and do not specifically pertain to lengthening while producing tension. Hence, eccentric contraction is the correct answer, as it distinctly describes the scenario in which muscles lengthen under load while still creating tension.