What is the nonmoving (fixed) portion of the muscle called?

The nonmoving, or fixed, portion of a muscle is referred to as the origin. This part of the muscle remains anchored to a stable structure, typically a bone, allowing the muscle to generate force and movement at its other end, called the insertion. When the muscle contracts, it pulls the insertion towards the origin, resulting in movement at the joint where the muscle crosses. Understanding the roles of origin and insertion is crucial in anatomy and physical rehabilitation because it helps explain how muscles work in concert to produce movement and maintain stability, particularly during activities that require strength and coordination.