The middle trapezius runs almost horizontally from the upper thoracic spinous processes to the scapular spine, providing the primary scapular retraction force that draws the scapula toward the spine and counters the protracted rounded shoulder posture. It is typically inhibited and underactive in individuals with forward head posture, making middle trapezius strengthening exercises (rowing, prone Y and T) foundational in shoulder rehabilitation programmes.
| Origin | Spinous processes of C7 through T3 |
|---|---|
| Insertion | Medial acromion and superior surface of the scapular spine |
| Nerve Supply | Spinal accessory nerve (CN XI); Cervical plexus (C3, C4) |
| Blood Supply | Transverse cervical artery |
| Actions | Retraction of the scapula — primary scapular retractor; Assists in upward rotation of the scapula |
|---|
By retracting the scapula, the middle trapezius positions the glenoid appropriately for glenohumeral joint mechanics — a retracted scapula optimises the length-tension relationship of the rotator cuff muscles and reduces impingement risk compared to the protracted position of a rounded shoulder.
Middle trapezius weakness in the face of pectoralis minor tightness and upper trapezius overactivity is the defining muscle imbalance pattern in shoulder impingement syndrome and thoracic kyphosis. EMG studies consistently show middle and lower trapezius inhibition alongside upper trapezius and upper pectoral overactivity in these patients. Rowing exercises at various angles of arm elevation target the middle trapezius preferentially.
The middle trapezius is palpable between the scapular spine and the thoracic spinous processes as the horizontal muscle fibres that become firm during scapular retraction exercises.
Middle trapezius inhibition producing excessive scapular protraction and anterior tilt that impairs rotator cuff mechanics and contributes to subacromial impingement, managed with specific lower and middle trapezius strengthening.
