Function

Trapezius is involved in a large number of movements:

• retraction of scapula: mainly produced by contraction of the horizontal central fibres medial to the scapular spine and assisted by more superior and inferior fibres
• elevation of scapula: mainly produced by contraction of superior fibres of trapezius. This motion not only permits shrugging of the shoulders - elevation - but also prevents depression of the shoulders when the pectoral girdle is being pulled downwards e.g. when carrying heavy weights in the hands
• lateral rotation of the scapula: this permits rotation of the glenoid cavity superiorly around a point near the base of the scapular spine. This movement is important in abduction at the glenohumeral joint. The lower trapezius fibres move the base of the spine inferiorly. The upper trapezius fibres elevate the acromion and lateral spine superiorly. Serratus anterior assists in this movement.
• extension of the neck: produced by bilateral contraction of the upper trapezius fibres
• lateral flexion of the neck: produced by unilateral contraction of the upper trapezius fibres
• stabilisation of the scapula: in combination with other muscles