Your arm is the link between your body and your ability to manipulate your environment. Your pecs, back and shoulder muscles must move your hand to the correct position for you to eat, brush your teeth, work, exercise and play sports. Tendons attach your muscles to your bones; they need less blood compared to your muscles.
Your muscle cells need plenty of oxygen and nutrients to survive and function. The cells in your tendons need very little oxygen and nutrients. Muscle cells are composed primarily of connected proteins that produce movement when they contract. Tendons are bundles of collagen connective tissue.
The largest muscle of your arm is your shoulder muscle, or the deltoid. It has three divisions--anterior, medial and posterior heads. Your deltoid muscle does not have a long, stringy tendon. Its primary function is to move your arm out to your side. The smaller muscles of your shoulder are the muscles of the rotator cuff. These muscles originate on your shoulder blade then insert on your humerus, the bone in your arm. Unlike the deltoid, these muscles have slightly longer tendons which are more prone to injury. According to a 2009 article by Anthony Sgherza, published by the American College of Sports Medicine, overuse movements like that of throwing a baseball may lead to inflammation of the rotator cuff tendons. The tendons may rub against the bony structures or may become impinged between the bones and bursa.
The muscle lying on the front of your arm is your biceps brachii. It has two divisions, a long head and a short head. Your biceps bend your elbow to draw your hand toward your shoulder. Both heads have long tendons originating off the top of your shoulder blade. The shorter inserting tendon runs just below the crease of your elbows. Typical bicep brachii injuries involve the tendon of the long head. Tendon ruptures and inflammation can occur from repetitive overhead throwing motions. The smaller muscles which bend your elbow are your brachialis and brachioradialis. Your brachialis lie under your biceps brachii with very short tendons. Feel your brachioradialis at the outer sides of your elbows with your palms faced up. This muscle actually has a long inserting tendon attaching to the end of one of your forearm bones, the radius.
Your triceps lie at the back of your arm functioning to straighten your elbows. It has three heads--the long head, medial head and lateral head. The originating tendons are short with the long head coming off of your shoulder blade. The short and medial heads arise from your arm bone. All heads come together in a short tendon to insert on the uppermost portion of your other forearm bone, your ulna.
Vary your workouts to prevent overuse injuries. If you experience sudden tendon pain, apply ice to the affected area, try not to move it and seek medical attention. If you have chronic pain, check with your doctor to prevent further injury.