Teres major and minor muscles can be defined as tiny back muscles, especially when compared to latissimus dorsi. They are actually even smaller that the deltoids. The teres muscles originate from the shoulder blades and insert into the arm bones or humerus. The primary role of teres minor is to rotate the upper arm outwards whereas the teres major muscles help in drawing the arm backwards to the middle of the body and also extend the upper arm behind and rotate the humerus inwards. Baseball pitchers use the teres major muscles repeatedly. The muscles are also used during so many other activities on a daily basis and there is therefore a need to keep them in top shape.