Teres Major and Teres Minor
The Teres Major is a thick ovoid-shaped muscle and the Teres Minor is a long, narrow muscle.
The teres major is sometimes referred to as the climbing muscle as it works in unison with the pectoralis major (pecs) and latissimus dorsi(lats) muscles to pull the trunk via adduction when its humeral attachment is fixed. This muscle also supports and helps to stabilize the lats, especially in wood-chopping movements. This muscle assists with the adduction (bringing closer to the body), internal rotation, and extension of the arm. The muscles only become active when there is resistance to these motions, and do not engage with normal, non-resisted motion.