Major Muscle Groups
The muscles of the back
The Rhomboids are the rhombus shaped muscles associated with the scapula. The rhombus muscles are responsible for the retraction of the scapula. There are 2 rhomboid muscles which are named:
The Rhomboid major
The Rhomboid minor
The Deltoids are the rounded shaped muscle off the shoulder, it is made up of 3 heads which are:
The front deltoid
The lateral deltoid
The rear (posterior) deltoid
The deltoids are the prime mover of arm abduction along the frontal plane.
The Latissimus dorsi is the large muscle in the back which is partly covered by the trapezius, it is responsible for extension, adduction, transverse, extension.
The Teres minor is the narrow, elongated muscle of the rotator cuff. This along with the infraspinatus attach to the head of the humerus; as part of the rotator cuff they help hold the humeral head in the glenoid cavity of the scapula. They help the rear deltoid to externally rotate the humerus, as well as performing transverse adduction, extension and transverse extension.
The Teres major is a muscle of the upper limb, it is a thick but flattened type of muscle. The teres major is a medial rotator and adductor of the humerus and assists the latissimus dorsi in drawing the previously raised humerus downward and backward (extension). It helps to also stabilise the humeral head in the glenoid cavity.