The long head of the triceps is the only triceps head to cross the shoulder joint, arising from the infraglenoid tubercle and crossing the inferior glenohumeral capsule. This makes it a weak shoulder extensor and adductor in addition to its elbow extension role. The long head is the most commonly strained triceps component, typically at its proximal musculotendinous junction during weight lifting. Its proximal tendon can impinge on the quadrilateral space structures when hypertrophied.
| Origin | Infraglenoid tubercle of the scapula |
|---|---|
| Insertion | Posterior surface of the olecranon via the common triceps tendon |
| Nerve Supply | Radial nerve (C7, C8) |
| Blood Supply | Posterior circumflex humeral artery; Profunda brachii |
| Actions | Extension of the elbow; Extension and adduction of the arm at the shoulder (long head only, due to its shoulder joint crossing); Compresses the inferior glenohumeral joint (long head crossing the inferior capsule) |
|---|
The biarticular nature of the long head makes it length-dependent — it is most effective as an elbow extensor when the shoulder is in full flexion (arm overhead) which lengthens it, and least effective when the shoulder is extended (arm at side or behind the body).
Triceps tendon injuries most commonly affect the distal triceps at the olecranon insertion rather than the proximal long head. However, long head strain at the infraglenoid tubercle origin produces posterior shoulder and upper arm pain reproduced by resisted elbow extension with the shoulder flexed. MRI distinguishes long head strains from distal biceps or posterior shoulder capsular pathology.
The triceps long head belly is palpable on the posterior upper arm medial to the lateral and medial heads, running from the axillary region to the olecranon.
Proximal musculotendinous junction injury from heavy overhead pressing producing posterior shoulder and upper arm pain reproduced by resisted elbow extension overhead.
