Shoulder pain could be caused by joint dislocation, joint inflammation, muscle tear or muscle spasm. They could happen because excessive activity of muscles, a fall or a blow to the shoulder as in a car accident.

A spastic muscle is a muscle, which was forced to contract and lost its ability to stretch. A spastic muscle also resists being exercised, stretched or massaged because these activities will over-stimulate the central nervous system. Once the muscle is in a spasm and its fibers have shortened, it has lost its ability to stretch. The muscle fibers will start to compress blood vessels, compromise blood circulation, entrap nerves, and compress joints.

The muscles, which could cause shoulder pain, are:

1. Scalenes - The Scalenes muscles which located in front, side and back of the neck have a powerful impact on neck structure and function. They can straighten the normal neck curvature, or even reverse it. The anterior and lateral scalenes could compress nerves, and will produce pain and radiation (tingling sensation and numbness) to the neck, shoulder, and arm down to the fingers.
   
   
2. Upper Trapezius - The Upper Trapezius and Levator Scapulae muscles connect the cervical vertebrae to the shoulder blades (scapulae) and upper thoracic spine. While in a spasm they will produce pain to the back of the neck, to the shoulder and headaches.
   
   
3. Latissimus Dorsi - This muscle originates in the lower back and is connected to the inside of the shoulder. When in a spasm the pain will be felt in the anterior part of the shoulder and the lower back.
   
   
4. Deltoid - This muscle overlaps the shoulder joint from the front, back, and the side. When in a spasm the pain would be felt in the shoulder itself with referred pain down the arm to the elbow.
   
   
5. Supraspinatus - This muscle is originated in the upper part of the scapulae (shoulder blade) and is connected to the shoulder joint. When in a spasm, the pain would be felt in the shoulder and all the way down the arm to the wrist.
   
   
6. Infraspinatus (Rotator cuff muscle) - This muscle covers the lower part of the scapulae (shoulder blade) and is connected to the shoulder joint from the back... When in a spasm, the pain would be felt between the scapulae and the spine and down the arm all the way to the fingers.
   
   
7. Teres minor (Rotator cuff muscle) - This muscle is originated in the lateral (outside) edge of the scapulae and is connected to the back of the shoulder joint. When in a spasm, the pain would be felt in the back and side of the shoulder.
   
   
8. Teres major - This muscle is originated in the lower edge of the scapulae and is connected to the anterior (front) part of the arm. When in a spasm, the pain would be felt in the side of the shoulder and in the back of the forearm.
   
   
9. Subscapularis - This muscle is originated in the anterior (front) part of the scapulae and is connected to the front part of the shoulder joint. When in a spasm, the pain would be felt the top and back of the shoulder and down the inner part of the arm and the wrist.
   
   
10. Pectoralis Major - This muscle is originated in the chest and is connected to upper part of the arm from the front. When in a spasm, the pain would be felt in the shoulder, chest and down the inner part of the arm to the elbow area.
    
    
11. Pectoralis Minor - This muscle is originated in the third, fourth and fifth ribs in the side of the rib cage. It. is connected to the front tip of the scapulae (coracoid process) in the shoulder joint. When in a spasm, the pain will be felt in the front part of the shoulder, the chest and down the inner arm to the fingers.
    
    
12. Subclavius - This muscle is between the 1st rib in the front and the clavicle (collar bone). When in a spasm the pain would be felt in the anterior (front) shoulder, and down the arm to the fingers.
    
    
13. Biceps Brachi - This muscle is connected between t he arm and the forearm. When in a spasm, the pain would be felt in the shoulder and down the arm to the thumb.
    
    
14. Triceps and Anconeus - These muscles are connected between the shoulder joint and the posterior (back) forearm. When in a spasm, the pain would be felt in the shoulder and the back of the arm and forearm.
    
    
15. Coracobrachialis - This muscle connects the front tip of the scapulae (coracoid process) to the anterior arm. When in a spasm, the pain would be felt in the shoulder and down the arm to the fingers.