How is the function of a muscle affected by active insufficiency?

Active insufficiency refers to the inability of a muscle to generate effective tension and produce movement when it is excessively shortened. This phenomenon occurs in biarticular muscles, which cross two joints, and it is most evident during positions where the muscle is fully contracted or fatigued at both joints it crosses.

When a biarticular muscle, such as the hamstrings or the rectus femoris, is shortened over both joints simultaneously, it reaches a point where it can no longer generate sufficient force to produce movement. This inability to contract further while in an overly shortened position leads to decreased functional capacity of the muscle, resulting in diminished force production.

Understanding active insufficiency is crucial for physical therapy practices, as it helps in tailoring rehabilitation exercises that avoid positions leading to this condition, thereby optimizing muscle function and performance during therapeutic activities.