Shoulder girdle muscles
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 which moves from action of the muscles. The muscles of the shoulder girdle are serratus anterior, pectoralis minor, levator scapulae, rhomboids and trapezius.
The Serratus Anterior muscle is used in activities which draw the scapula forwards. It is used strongly in push-ups and bench presses. Winged scapula are 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.