The deltoid is a powerful mover of the humerus. It allows the shoulder joint to do movements like extension, flexion and abduction. The deltoid muscle has a characteristic multipennate form of construction. This muscle packs a lot power for a relatively short lever arm. If you examine closely, the deltoid actually has three regions or referred to as heads. All of these heads are attached to the humerus. Most of the time when people talk about the shoulder muscles, they usually refer to the deltoid. The deltoid muscles receive its signal from the axillary nerve which originates in the neck. This is the reason why shoulder and neck problems, most if not all of the time, go together.
The Pectoralis Major
The pectoralis major muscles are effective in flexing the shoulder joint. It is located at the chest region of the abdomen and it makes up the bulk of the muscles located in the chest. The pectoralis major muscles allow for the humerus to be flexed. It also permits the humerus to do adduction and medial rotation.
Considered to be one of the largest muscles in the body, it is responsible for the brute force of the humerus. It functions primary as an extensor muscle and is known more commonly as the lats. It permits the shoulder joint to perform four movements, namely extension, adduction, transverse extension and internal rotation. With all the good things being said about the latissimus dorsi, it does have one flaw. It does not permit hyperextension of the shoulder. In some aspect it can stronger than the shoulder adductor and shoulder extensor.
Located posterior to the shoulder, the teres major muscle is a primary medial rotator of the shoulder joint. It is because the tendon is located on the anterior aspect of the humerus which gives it the mechanical advantage for the movement. It has a funny name that people refer to it, lats little helper. Most therapists ignore this muscle because it is rarely inflamed.
The coracobrachialis muscle got its name from its point of origin, the coracoids process of the scapula. It is, however, not an important muscle in flexion or adduction.
Both heads of the biceps brachii are active in resisted flexion. When the forearm is supinated, it is a strong elbow flexor. Body builders like to exercise this muscle by doing biceps curl because the improvement is relatively evident
The triceps brachii is not a significant mover in extension of the shoulder joint. More commonly known as the triceps muscle, this muscle enables a person to do push ups and to straighten the arms.
These muscles all work together to give the shoulder joint its flexibility and strength. Basic knowledge on the anatomy of these structures will give us the knowledge on how to strengthen and take care of these muscles.