Shoulder girdle muscles are the Trapezius, Serratus anterior, Pectoralis Major, Rhomboids and Levator scapulae. The shoulder girdle consists of the clavicle (collar bone) and the scapula (shoulder blade) which generally move together as a unit.
Only the clavicle connects directly to the rest of the skeleton at the sternum bone. It is really only the scapula that moves from the action of the muscles.
The Serratus Anterior muscle is used in activities that draw the scapula forward. It is used strongly in push-ups and bench presses. Winged scapula is an indicator of having a weak Serratus Anterior muscle.
The Pectoralis Minor muscle is the smallest of the two pectoral (chest) muscles. It works together with Serratus anterior which protracts and rotates the scapula upwards. When the two work together, pure protraction (without rotation) is produced.
Shrugging the shoulders (scapula elevation) requires the use of levator scapulae and Trapezius. Fixation of the scapula by other muscles, allows the levator scapulae muscles to work together to aid cervical extension, or independently to laterally flex (side bend) the neck towards the side of the working muscle.
There are two rhomboid muscles – Rhomboid Major and Rhomboid Minor. Rhomboid major is larger and positioned below rhomboid minor. Chins and dips are excellent activities for developing these muscles.
The trapezius muscle (Trapz) is a large muscle consisting of four parts covering the upper back, shoulders, and neck. It is used in shrugging the shoulders and with overhead movements.
- Part 1: Upper fibres of the cervical vertebrae. This is the weakest part of the muscle and only provides minor elevation of the clavicle.
- Part 2: The area commonly known as upper trapz. This is a strong elevator, rotator, and retractor of the scapula.
- Part 3: The mid-portion of the Trapzius. These fibres are mainly responsible for scapula retraction.
- Part 4: The lower fibres of Trapezius. This part of the muscle assists in retraction and rotation.