The shoulder is a ball-and-socket joint that moves in many different directions. Shoulder flexion -- lifting the arm out in front of the body and up overhead -- is a movement used in many daily activities. There are several muscles that produce shoulder flexion.
Pectoralis Major
The petoralis major is a large, strong muscle that produces shoulder flexion. It is located in the front of the chest and attaches by tendon to the humerus, or upper arm bone. It is innervated by both the lateral and medial pectoral nerves. The pectoralis muscle is the main shoulder flexor and is important for muscle definition in the chest.
Anterior Deltoid
The deltoid muscle is composed of three parts: anterior, middle and posterior. The anterior deltoid muscle is located on top of the shoulder and originates on the collarbone. The anterior deltoid tendon attaches to the front of the humerus producing shoulder flexion. The deltoid muscle is innervated by the axillary nerve.
Biceps: Long Head
The biceps brachii muscle splits into two tendons at the shoulder: the long head and the short head. The long head of the biceps muscle assists other muscles with shoulder flexion. It is located in the front of the upper arm and attaches to the glenoid fossa, or "socket" part of the shoulder joint. The long head of the biceps muscle is innervated by the musculocutaneous nerve.
Coracobrachialis
The coracobrachialis is a small muscle that also produces shoulder flexion. It originates from a protrusion on the shoulder blade called the coracoid process, and attaches to the humerus bone. The coracobrachialis is innervated by the musculocutaneous nerve.
Teres Major and Subscapularis
The teres major and subscapularis muscles assist other muscles with shoulder flexion. The teres major originates on the shoulder blade and its tendon attaches to the front of the humerus bone; it is innervated by the lower subscapular nerve. The subscapularis muscle covers the front surface of the shoulder blade and its tendon attaches to the humerus bone. The subscapularis is innervated by the upper and lower subscapular nerves.