Triceps

The triceps brachii (Latin for "three-headed muscle of the arm"), often shortened to triceps, is a large muscle on the posterior of the upper limb of many vertebrates. It is the muscle primarily responsible for extension of the elbow joint, straightening the arm.

Structure

The triceps brachii muscle has three heads:

• Long head: Originates from the infraglenoid tubercle of the scapula, and runs along the posterior aspect of the humerus. It is the only head that crosses the shoulder joint.

• Lateral head: Originates from the posterior surface of the humerus, superior to the radial groove.

• Medial head: Originates from the posterior surface of the humerus, inferior to the radial groove. It is deep to the long and lateral heads.

The three heads converge and insert via a single tendon onto the olecranon process of the ulna.

Function

The primary action of the triceps brachii is to extend the forearm at the elbow joint. The long head also contributes to adduction and extension of the arm at the shoulder joint. The medial head is the primary head active in all elbow extensions, while the lateral head is primarily active during more forceful extensions. The long head is recruited under conditions of elbow extension against resistance and shoulder adduction.

Innervation

The triceps brachii is innervated by the radial nerve.

Variation

A slip of muscle from the latissimus dorsi sometimes joins the long head of the triceps.

Clinical Significance

Triceps injuries are less common than biceps injuries. They usually occur due to direct trauma or overuse. Weakness of the triceps can result from radial nerve damage.

Training

The triceps can be strengthened through various exercises such as close-grip bench presses, triceps extensions (overhead, lying, cable), dips, and push-ups.