latismus dorsi
The latissimus dorsi and pectorals major are synergists for shoulder adduction
tibialis anterior
The large broad sheet of muscle you are referring to is the latissimus dorsi. It is responsible for movements like shoulder extension, adduction, and medial rotation of the arm.
The muscle of the pectoralis is antagonist to the latissimus dorsi during the shoulder adduction. The anterior fibers are involved in shoulder abduction when the shoulder is externally rotated.
latissimus dorsi
Because shoulder horizontal adduction is performed when the arm is horizontal position (i.e., the elbow is level with shoulder) and adduction is movement toward the center of the body, shoulder horizontal adduction is performed primarily by pectoralis major and anterior deltoid, with an assist by latissimus dorsi.
Do you mean flexion and (abd)uction?? If so, the prime mover would be the deltoid muscle with many smaller muscles assisting. If you are in fact meaning flexion and adduction, the prime mover would be the pectoralis major and the latissimus dorsi with many smaller muscles assisting.
There are four muscles used for horizontal adduction of the shoulder. These muscles are the pectorals major, middle deltoid, latissimus dorsi, and coracobrachilis.
lattissimus dorsi
Shoulder adductors. Abduction means moving away from the median plane of the body and adduction means moving towards the median plane of the body.
latissumus dorsi is one among the superficial muscles of the back. it is supplied by the thoracodorsal nerve(C6,7,8). Actions extension and medial rotation of the arm. also known as climber's muscle & swimmer's muscle. it helps in the adduction of the arm. it helps in elevating the body, so considered as climber's muscle.