The deltoid muscle is used in all side lifting movements and any movement of the humerus on the scapula. It is divided into three portions, anterior, middle and posterior, with the fibres having different roles due to their orientation.
The Infraspinatus muscle is one of the four rotator cuff muscles crossing the shoulder joint and is commonly injured. It is the main external rotator of the shoulder joint.
Teres Minor is one of the four rotator cuff muscles surrounding the shoulder. Its main action, along with Infraspinatus is to externally rotate the shoulder joint. There are two Teres muscles, the other being Teres Major.