Pectoralis Muscles

The term is derived from the Latin pectus, meaning the breast area. There are two muscles, pectoralis major which is prominent, and pectoralis minor which is hidden. The prominent muscle is the one the muscle builders refer to as the “pecs.”

Pectoralis major is the anterior portion of a sheet of muscle which includes the trapezius posteriorly and the deltoid laterally; all find attachment to the collar bone (clavicle). The central bony attachment of pectoralis major is from the medial half of the clavicle, the margin of the breast bone (sternum), the ribs, and the thick fascia over the abdominal muscles. There are easily recognisable three segments of the muscle, functioning collectively or separately. As the fibers pass laterally, the lowermost pass behind the uppermost, forming a rounded lower border at the anterior wall of the armpit (axilla) converging on the tendon which is inserted into the humerus.

The muscle functions in drawing the arm to the body, as in pulling down a rope, or the body to the arm, whichever is fixed, as in raising oneself on a beam.

Pectoralis minor is completely hidden beneath major. Its medial attachment is to the 3rd, 4th, and 5th ribs; the fibers pass up and out to attach to the coracoid process of the shoulder blade (scapula). The tip of this process is easily felt below the mid-point of the clavicle.

Although this muscle will stabilize the shoulder blade when the arm is used, and to an extent pull the arm forward around the chest (protraction) it is probably of most value as a secondary muscle of respiration. The runner will unconsciously hold his hips when standing out of breath following a race – what in fact he is doing is to stabilize the scapula so pectoralis minor can assist in lifting the ribs to enhance the volume of air entering the chest in forced inspiration.