The pectoralis (pec) major muscle is the large, fan-shaped muscle across the chest. The pectoralis minor muscle is a much smaller muscle underneath the pec major. The pec major attaches in many places. There are separate attachments along the breastbone, collarbone, and into the upper arm (humerus).

Depending on how the rupture occurs, different portions of the tendon may be injured. A partial rupture means that one or more sections have torn away from their attachments. A complete rupture usually refers to a severed tendon as it inserts into the humerus.

An MRI is usually needed to show the full extent of the injury. It will show whether the rupture is partial or complete and the amount of muscle retraction. In acute injuries MRI shows if there's any bleeding or swelling in the area. In chronic injuries scarring and fibrosis can be seen.

For low-demand activities, a partial rupture can be treated conservatively. This means a rehab program but no surgery is needed. For someone like you who is a manual laborer, surgery to repair the tear may be the best option. A delay in treatment can result in weakness and loss of motion.