The shoulder is a very important area in the human body. It is made up of three bones which include the clavicle, scapula and the humerus. It also has several key muscles, tendons and ligaments. The place where the bones articulate make up the shoulder joints. We will discuss the different groups of shoulder muscles (also called the deltoids) which are very important when following a bodybuilding routine or a general fitness plan in order to achieve a symmetrical physique that is well-balanced.
Exercise Guides For Your Shoulders!
The muscles of the shoulder are divided into three major groups. These include the extrinsic muscles, intrinsic muscles and the muscles that connect the shoulder to the arm. There are several key shoulder muscles along with secondary muscles in the shoulder region and we will discuss how these all interact with each other.
Extrinsic Muscles (Superficial) Consist of Four Different Muscles:
- Deltoid Muscle. This is the main muscle of the shoulder. It is also what gives the shoulder its shape. The deltoid muscle has three parts: the anterior, medial and posterior (front, middle, rear). The anterior starts from the anterior and upper part of the body, the middle starts from the acromion process while the posterior is located in the lower part of the spine and the scapula. Together they insert to the humerus allowing the arm to flex medially and to rotate. It also contributes to lifting the arm when it’s away from the body.
- Trapezius Muscle. It starts from the back of the skull and moves along the spinal vertebrae. It goes to the collar bone, spine of the scapula and acromion of the scapula. Its main function is to raise the shoulder and helps rotate the scapula when reaching upwards.
- Pectoralis Major Muscle. It has two heads which includes the clavicular head and the sternocostal head. The clavicular head starts in the midline of the collar bone while the sternocostal starts from the chest plate area. The main function of this muscle is to support and provide movement of the front part of the shoulder. It inserts near the humerus which enables the arm to move inward, rotates the glenohumeral joint and also enables the arm to flex.
- Latissimus Dorsi Muscle. This is the muscle that brings the arm closer to the body and helps to rotate the arm. It also helps to lower the shoulder and keeps the lower part of the scapula near the chest wall. It starts from the lower thoracic vertebrae and the iliac crest of the lower ribs and pelvic bone. It also inserts into the humerus at the intertubercular groove.
Intrinsic Muscles (Cannot Be Seen on The Surface)
Intrinsic muscles are also known as “deep muscles”. This group is composed of the front muscles, back muscles, side muscles and rotator cuff muscles:
- Front Muscles. These muscles include the pectoralis minor muscle which helps in moving the scapula downward, forward and raising the ribs. The pectoralis minor is located deep in the pectoralis major muscle. It moves through the 3rd and 5th rib extending out to the coracoid process in the spatula. The front muscles also include the subclavius muscle also found in the pectoralis major muscle. It runs from the first rib to the collar bone. Its purpose is to help the shoulder to move downward and forward while stabilizing the collar bone.
- Back Muscles. These muscles consist of the rhomboid major and minor muscles, levator muscle and teres major muscle. The rhomboid muscle runs from the vertebrae travelling to the middle part of the scapula. This helps the scapula move up. The teres major moves from lower part of the scapula and attaches to the anterior part of the humerus making it to rotate and extend the arm. The levator scapulae muscle starts from the neck vertebrae and attaches itself to the upper and medial part of the scapula allowing it to raise up.
- Side Muscles. These include the serratus anterior muscles which starts from the first nine ribs and passes through the chest wall to the medial side of the scapula. It works to bring the scapula to the chest wall and rotates it.
- Rotater Cuff Muscles. They consist of supraspinatus, infraspinatus and teres minor and subscapularis muscles. Their main function is to stabilize the shoulder joint and rotate the arm medially.
Important Muscles Around The Shoulder:
- Biceps Brachii Muscle. This muscle helps flex the shoulder and the forearm. It has a long head starting from the supraglenoid tubercle of the scapula and short head from the coracoid process of the scapula and they both insert in the medial area of the forearm.
- Coracobrachialis Muscle. It works to stabilize the humerus. It moves from the coracoid process and inserts to the humerus to help move the arm towards the body.
- Triceps Brachii Muscle. Its main function is to extend the forearm at the elbow. It also helps to extend the arm and draw the humerus into the body. It has a head running from the infraglenoid tubercle of the scapula, another head at the upper part of the humerus and one at the lower part of the humerus. They all connect at the olecranon process of the ulna.