The latissimus dorsi muscle can contribute to pain in the shoulder, upper back, and arm going down into the hand. The muscle can also cause pain in the side of the ribcage and lower abdomen. It is the muscle that most often causes the 'side stitch'.
Scalene muscles are a prime contributor to thoracic outlet syndrome as well as neck, shoulder, chest, upper back and arm pain. Muscle twitching, jerking and restlessness similar to restless leg syndrome felt in the neck and shoulder is a classic sign of scalene dysfunction
The coracobrachialis muscle connects the shoulder to the upper arm. It can contribute to pain in the shoulder, back of the arm, and occasionally the middle finger. Pain is often felt when attempting to put your hand behind your back and or raising your arm over your head.
The biceps brachii muscle is found in the front of the upper arm. It contributes to pain in the shoulder, upper arm and elbow. Straightening the arm when the palm is facing up can be painful and difficult.
The pectoralis major contributes to pain in the chest, shoulder, breast and upper back. Pain can also travel down the inner arm, elbow and extend to the hand and last two fingers.
The deltoid is the muscle that covers the tip of the shoulder. It contributes to pain in the shoulder and upper arm. One indication of problems with the deltoid muscle is pain is most intense during activity and subsides when resting the shoulder and arm.
The infraspinatus muscle lines the back of the shoulder blade. It is one of the muscles that can contribute to frozen shoulder. The muscle can cause pain in the shoulder, neck, pain down the outside of the arm which descends down into the thumb and hand. Shoulder mobility can be greatly reduced.
The supraspinatus muscle is one of the four rotator cuff muscles. It contributes to pain in the shoulder, outside of the arm and elbow. Pain is a deep aching that often persists during rest.
The brachialis muscle connects the upper arm to the lower arm. It contributes to pain in the upper arm, elbow, thumb pad and thumb. It can also cause tingling and / or numbness in the back of the forearm into the thumb. Bending and straightening the elbow is painful.