The triceps brachii is the sole extensor of the elbow joint, composed of three heads, a long head spanning both the shoulder and elbow, and two shorter heads originating exclusively from the humerus, all converging into a broad tendon that attaches to the olecranon. As the largest muscle of the upper arm by volume, it is essential for any pushing movement and for stabilising the elbow during loaded activities. The long head also plays a meaningful role at the shoulder, assisting adduction and extension during pulling and throwing.
| Origin | Infraglenoid tubercle of the scapula; Posterior surface of the humerus above the radial groove; Posterior surface of the humerus below the radial groove |
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| Insertion | Posterior surface of the olecranon process of the ulna |
| Nerve Supply | Radial nerve (C6, C7, C8) |
| Blood Supply | Deep brachial artery; Superior and inferior ulnar collateral arteries |
| Actions | Extension of the elbow, the only muscle capable of this; Extension and adduction of the shoulder (long head only) |
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Its primary function is straightforward, elbow extension, but the long head's dual-joint span means the triceps also contributes to decelerating the arm during overhead throwing and provides dynamic stability to the posterior shoulder capsule during loaded activities.
Triceps tendinopathy, sometimes called 'triceps tendinitis,' produces posterior elbow pain that is reproduced by resisted elbow extension and can be mistaken for lateral epicondylalgia in the early stages. The distal triceps tendon can rupture from a fall on an outstretched hand or a sudden eccentric overload during pushing, leaving the person unable to extend the elbow against gravity. The radial nerve travels directly behind the humerus in the spiral groove adjacent to the lateral and medial heads, making it vulnerable to direct compression or humeral shaft fractures, a 'Saturday night palsy' scenario.
The three heads of the triceps are palpable along the entire posterior upper arm. The distal tendon is firm and easily felt just above the olecranon, and becomes taut with resisted elbow extension in any position.
An uncommon but significant injury caused by sudden eccentric loading on an extended elbow, producing posterior elbow pain, swelling, a palpable gap above the olecranon, and inability to extend the elbow against gravity.
Degenerative changes in the distal triceps tendon from repetitive overloading during pressing or throwing, producing posterior elbow aching that worsens with prolonged extension activities and is tender directly over the olecranon attachment.
Compression of the radial nerve against the humeral spiral groove, from prolonged external pressure or humeral fracture, causes triceps weakness along with wrist drop and loss of finger extension, as the nerve supplies all the muscles it encounters distal to this point.
