The muscles that move the forearms can be divided into four groups: forearm flexors, forearm extensors, forearm pronators, and forearm supinators. The flexors and extensors act on the elbow joint, while the pronators and supinators act on the radioulnar joints.
Forearm Flexors
The biceps brachii, brachialis, and brachioradialis are forearm flexors. The biceps brachii is made up of two heads. Its long head originates at the supraglenoid tubercle of the scapula, whereas that of the short head is at the coracoid process of the scapula. The heads merge and insert at radial tuberosity. A fibrous membrane known as bicipital aponeurosis emerges from the distal end of the biceps brachii and inserts into the deep fascia of the forearm. The anterior surface of the humerus is the origin site for the brachialis muscle. It inserts into the ulnar tuberosity and coronoid process of the ulna. The brachioradialis muscle originates on the lateral border of the distal end of the humerus and inserts on the radius, superior to the styloid process.
Forearm Extensors
The triceps brachii, and anconeus are forearm extensors. The triceps brachii is a three-headed muscle. Its long head originates on the infraglenoid tubercle. The lateral head originates from the lateral and posterior surface of the humerus. The posterior surface of the humerus is also the origin point for the medial head. Together, the three heads are inserted at the olecranon of the ulna. Finally, the anconeus originates from the humerus at the lateral epicondyle and inserts on the olecranon and superior portion of the ulnar shaft.
Pronators and Supinators
Pronator teres and pronator quadratus are forearm pronators. The pronator teres originate from the medial epicondyle of the humerus and the coronoid process of the ulna. It inserts on the mid-lateral surface of the radius. The pronator quadratus originates on the distal shaft of the ulna and inserts onto the distal part of the radius. The supinator muscle supinates the forearm. It originates from the lateral epicondyle of the humerus and the ridge near the radial notch of the ulna. It inserts on the lateral surface of the proximal one-third of the radius.
