The insertion of a muscle refers to the point where the muscle attaches to the bone that it moves. In contrast to the origin, which is the fixed attachment point that does not move when the muscle contracts, the insertion site moves during muscle contraction. This characteristic is crucial for understanding how muscles work to produce movement at joints.
For instance, consider the biceps brachii muscle in the upper arm. Its origin is at the shoulder, while its insertion is on the radius bone of the forearm. When the biceps contracts, it pulls on the radius, bending the elbow and allowing the forearm to move upwards. Therefore, recognizing the insertion as the movable attachment helps in grasping how muscular movements function and how they are coordinated during various physical activities.