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 |
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| 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 |
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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 often affect the distal tendon at the olecranon rather than the proximal long head. Long head strain or traction tendinopathy at the infraglenoid tubercle, seen in overhead athletes and heavy pressers, produces posterior shoulder and upper arm pain reproduced by resisted elbow extension with the shoulder flexed, and is managed with progressive eccentric loading. MRI distinguishes it from posterior capsular and labral problems. The long head forms boundaries of the quadrangular space (with teres minor, teres major and the humerus) and the triangular space, so it is a key landmark for the axillary nerve and posterior circumflex humeral artery and for the radial nerve in the triangular interval below.
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.
