Final answer:
An eccentric contraction is the muscle action that involves lengthening of the muscle fibers while attenuating force. It occurs during activities such as lowering a weight in a gym exercise, which contrasts with muscle shortening seen in concentric contractions.
Step-by-step explanation:
The type of muscle contraction/action that attenuates force through muscle fiber lengthening is known as an eccentric contraction. In an eccentric contraction, the muscle lengthens as it maintains tension, such as when lowering a weight in a slow and controlled manner.
This contrasts with concentric contractions where the muscle shortens, and isometric contractions where the muscle length does not change. Eccentric contractions are important in both movement and body balance. An example of eccentric contraction is when you lower a hand weight down slowly, causing the biceps brachii to increase in length even as it controls the descent of the weight.