Shoulder muscles contain areas with poor blood flow. Tissues with good blood circulation are more successful and faster in repairing themselves. The area where the blood circulation is weak and the shoulder muscles adhere to the bone deteriorates and degenerates with age.
This region, especially in overhead activities, can also be compressed by the bone (acromion) and can be torn over time. It can be seen more frequently in athletes who do overhead movements frequently, but activities that routinely use the shoulder joint, such as cleaning windows, washing cars, and painting, can also cause shoulder muscle tears. Again, falling on the shoulder can cause a tear in this muscle group.