The triceps brachii is a large muscle occupying the entire back surface of the upper arm, extending from the shoulder blade down to the elbow. Its name, derived from the Latin for “three-headed arm muscle,” describes its unique structure. This muscle is a major component of arm mass and plays a significant role in nearly all arm movements, such as pushing a door or throwing a ball. It is a frequent focus in fitness and strength training programs due to its visibility and functional importance.
Structure and Location
The Triceps Brachii has three separate points of origin, or “heads”: the long, lateral, and medial heads. The long head is the only one that originates on the scapula, specifically at the infraglenoid tubercle, meaning it crosses both the shoulder and elbow joints. The lateral and medial heads both originate directly on the humerus.
The lateral head begins on the posterior surface of the humerus, superior to the radial groove, while the medial head starts inferior to that groove. All three muscle bellies converge roughly halfway down the upper arm to form a single, strong tendon. This tendon inserts onto the olecranon process, the bony projection at the back of the ulna. The medial head is situated deepest, lying beneath the other two, while the lateral head is the most visible on the outer part of the arm.
Primary Role in Movement
The main function of the triceps brachii is to extend the forearm, which is the action of straightening the arm at the elbow joint. This makes it an extensor muscle and the direct antagonist to the biceps brachii. When the triceps contracts, the biceps relaxes. This movement is used in countless everyday actions, such as pushing objects, reaching out, or maintaining a straight arm against resistance.
The three heads often work together, but they may be activated differently depending on the movement. Due to its attachment to the scapula, the long head has a secondary role at the shoulder joint, assisting in the extension and adduction of the arm. This dual-joint function means the long head is often engaged when the arm is positioned overhead or extended behind the torso.
Strengthening the Muscle
Strengthening the triceps involves training all three heads. Compound pushing movements, which involve multiple joints, are highly effective for building overall triceps mass and strength. Examples include close-grip bench presses, overhead presses, and diamond push-ups, which engage the triceps alongside the chest and shoulders.
Isolation exercises, which focus specifically on the elbow joint, are useful for targeting individual heads. Overhead triceps extensions and skull crushers are beneficial because the overhead position puts a significant stretch on the long head, promoting its engagement. Conversely, movements where the arm is by the side, such as cable pushdowns, place greater emphasis on the lateral and medial heads. Using an underhand or reverse grip on a pushdown can also help stress the medial head.
Common Issues and Injuries
The triceps is susceptible to several common issues. Triceps tendonitis is frequent, often caused by overuse or repetitive strain, particularly in throwing athletes or weightlifters. Symptoms include pain and tenderness at the back of the elbow, which worsens when straightening the arm.
Muscle strains happen when the muscle fibers are injured, with the long head being a common site. A more severe, though rare, injury is a triceps tendon rupture that can significantly limit the ability to extend the arm. Persistent pain, swelling, or an inability to move the arm fully are signs that a professional diagnosis and treatment plan should be sought.