The lengthening of an activated muscle is called:

The lengthening of an activated muscle is referred to as eccentric muscle action. During this type of contraction, the muscle generates tension while it is being elongated. This contraction occurs when the muscle is actively resisting a force that is causing it to stretch, such as when exerting control during a descent or lowering phase of an exercise. For instance, when performing a squat, as you lower your body, the quadriceps undergo an eccentric contraction to control the movement against the force of gravity.

Understanding this type of muscle action is crucial for personal trainers, as it plays a significant role in muscle development, injury prevention, and functional movement patterns. Eccentric actions are often associated with the elongation of the muscle in response to an external load and are also important for maximizing strength gains and enhancing performance in various physical activities.