The muscles of the shoulder joint are those which function to move the upper arm bone. Movements which are possible at this joint include flexion, extension, abduction, adduction, internal and external rotation.
Shoulder joint muscles can loosely be grouped into the four rotator cuff muscles which rotate the shoulder (Supraspinatus, Infraspinatus, Subscapularis and Teres minor) and the large global muscles which flex, extend, adduct and abduct it (Pectoralis Major, Latissimus dorsi, Deltoid)
Shoulder Joint Movements Explained
Flexion - raising the arm up in front and above the head.
Extension - taking the arm back behind.
Abduction - moving the arm out to the side and aobe the head.
Adduction - bringing the arm in towards and across the body.
External rotation - twisting the arm out, away from the body.
Internal rotation - twisting the arm in, towards the body.