The lower trapezius is the inferior portion of the trapezius muscle, characterised by its oblique upward course from the lower thoracic spinous processes to the scapular spine. It is the primary scapular depressor and a key component of the lower trapezius-serratus anterior force couple that rotates the scapula upward during arm elevation. Its inhibition in shoulder impingement, rotator cuff disease, and overhead athlete fatigue is a central rehabilitation target.
| Origin | Spinous processes and supraspinous ligaments of T6-T12 (the lower fibres, running obliquely upward to the scapular spine) |
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| Insertion | Medial spine of the scapula and the scapular spine root (the lower fibres pull the scapular spine inferiorly and medially, rotating the glenoid upward) |
| Nerve Supply | Spinal accessory nerve (CN XI) providing motor supply; proprioceptive fibres via C3-C4 cervical plexus |
| Blood Supply | Transverse cervical artery (descending branch) and posterior intercostal arteries |
| Actions | Depresses the scapula; tilts the scapular spine inferiorly producing upward rotation of the glenoid (working with the serratus anterior and upper trapezius as the force couple for overhead elevation); adducts (retracts) the scapula medially; the most important scapular stabiliser for overhead activity coordination |
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Lower trapezius weakness is the most consistently identified scapular dyskinesia pattern in shoulder impingement and rotator cuff disease: its inhibition reduces upward glenoid rotation during overhead activity, producing relative supraspinatus impingement against the coracoacromial arch. Exercises specifically targeting the lower trapezius (prone Y and T exercises, scapular depression against resistance) form the foundation of shoulder impingement rehabilitation. CN XI injury during neck dissection denervates the trapezius producing the dropped shoulder deformity, winging, and shoulder pain from loss of all trapezius components.
Lower trapezius weakness reduces upward scapular rotation during overhead arm elevation, allowing impingement of the supraspinatus and subacromial bursa against the coracoacromial arch; targeted lower trapezius exercises (prone T and Y, serratus anterior push-up plus) restore the force couple for upward rotation and reduce impingement symptoms.
