What is active insufficiency?

Active insufficiency occurs when a muscle is unable to shorten further due to being in a fully shortened position, which means the muscle cannot generate effective tension to produce movement at the joint. This phenomenon typically happens in two-joint muscles, where the muscle is maximally contracted across one joint, which reduces its ability to produce force at the other joint it spans.

For example, in the case of the biceps brachii, when someone attempts to flex their elbow while their shoulder is also fully flexed, the biceps may be at a point where it cannot shorten anymore. This results in decreased power or weakness in the elbow flexion because the muscle is stretched across both joints. Understanding active insufficiency is critical for physical therapist assistants to facilitate appropriate rehabilitation exercises and ensure optimal muscle performance during activities.