Mobile end

Punctum mobile

Definition

Muhammad A. Javaid

Most skeletal muscles are attached to bones at two ends — a fixed end and a mobile end.

  • Fixed End (Origin): This is the attachment site that remains relatively stable during muscle contraction. It is usually proximal (closer to the body’s midline or trunk) and provides a stable base from which the muscle acts.

  • Mobile End (Insertion): This is the attachment site that moves when the muscle contracts. It is typically distal (further from the body’s midline or trunk) and is drawn toward the fixed end during movement.

Example

In the biceps brachii, the scapula provides the fixed end (origin), while the radius forms the mobile end (insertion). During elbow flexion, the forearm (insertion) moves toward the shoulder (origin).

Clinical note

The distinction between fixed and mobile ends can reverse depending on the action — for example, during pull-ups, the forearm becomes the fixed end while the scapula moves, demonstrating reversal of muscle action.

References

  • Gray, H. (2016) Gray’s anatomy the anatomical basis of clinical practice. 41st edition. Edited by S. Standring. New York: Elsevier.