Pectoralis Muscle

The anterior chest wall comprises the pectoral regions. It contains four major muscles that exert a force on the upper limb: the pectoralis major muscle, the pectoralis minor muscle, serratus anterior, and subclavius. Pectoral muscles are the muscles that connect the front of the human chest with the bones of the upper arm, shoulder, and the rib cage. 

Pectoralis major muscle is a thick fan-shaped muscle, making the bulk of chest muscle. The purpose is to flex, extend, and rotate the humerus, the long bone of the upper arm. Pectoralis minor muscle is a thin, triangular muscle located beneath the pectoralis major muscle which is attached to the ribs and serves to stabilize the scapula - the large bone of the shoulder. The pectoral fascia is a thin layer of tissue over the pectoralis major muscle, that extends towards the latissimus dorsi muscle on the back. Along with pectoralis major and minor, the subclavius muscle forms the axilla or armpit and the serratus anterior is on the front of the chest and moves the scapula forward around the torso for example while throwing a punch. These are the muscles of the pectoral region.

Pectoralis Major and Minor Muscles

Pectoralis Major Muscle

The pectoralis major muscle is the larger and more superficial muscle. Pectoralis major  originates from distinct places. It originates at the clavicle or the collarbone, the sternum, the ribs and a tendinous extension of the external oblique abdominal muscle. It extends across the upper part of the chest and is attached to a ridge at the rear of the humerus i.e. the bone of the upper arm. From these origins, the fibres converge to the pectoralis major insertion. The ones arising from the clavicle pass obliquely downward and laterally outward and are separated from the rest by an interval. Those originating from the lower part of the sternum and the cartilages of true ribs run upward and laterally and the middle fibres pass horizontally. The pectoralis major is shown in the given diagram below:

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The pectoralis major muscle ends in a flat tendon which is inserted into the lateral lip of the bicipital groove of the humerus.

The pectoralis major function is to move the shoulder joint. The actions that are facilitated by pectoralis major include, flexion, adduction or depression, and rotation. These functions allow us to do activities such as lifting a child, flapping the arms, and arm-wrestling respectively. These are helpful when the raised arms are fixed for example in climbing where it aids the latissimus dorsi and teres major muscles in pulling. Importantly, the pectoralis major muscle keeps the arm attached to the trunk body. 

The pectoralis major muscle can be targeted by various exercises such as plating and bench press, etc. Although these exercises are important for pectoralis major activation, it is necessary to be careful while following the routine of the exercises so that there is no tear and no damage to the muscles. 

Pectoralis Minor Muscle

The pectoralis minor muscle lies under the pectoralis major. It starts from the middle of the ribs i.e. the upper and outer surfaces of the third, fourth, and fifth ribs, also from near their cartilages and from the aponeuroses covering the intercostalis and inserts into or attaching to the scapula or the shoulder blade. The given below diagram shows the origins and insertions of pectoralis minor muscle:

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The pectoralis minor helps in moving the shoulder forward and downward which physiologically opposes the trapezius muscle. The pectoralis minor pushes down the point of the shoulder, which draws the scapula superior towards the thorax and throws its inferior angle posteriorly.

Thus, the pectoral region houses important pectoralis muscle - the pectoralis major muscle and the pectoralis minor muscle that not only provide locomotive flexibility to the shoulder and the arms but also keep them attached to the main body and with the ribs. This pectoralis is known as ‘pecs’ or ‘chest muscles’ as well. Most of the chest building exercises are centred around the activation of the pectoral muscles.