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The biceps brachii, brachialis, and brachioradialis are the primary forearm flexors. The biceps brachii is a two-headed muscle on the anterior upper arm that flexes the elbow and supinates the forearm. The brachialis lies beneath the biceps and assists in elbow flexion. The brachioradialis, located on the lateral forearm, flexes the elbow and enables both pronation and supination movements.

The biceps brachii is a two-headed muscle with heads originating at the supraglenoid tubercle and coracoid process of the scapula, inserting at the radial tuberosity. The brachialis originates on the anterior humerus and inserts into the ulnar tuberosity and coronoid process of the ulna. While both flex the elbow, the brachialis lies directly beneath the biceps and provides additional flexion strength.

The triceps brachii is a three-headed muscle located at the back of the upper arm that extends the forearm at the elbow joint and the arm at the shoulder joint. Its three heads originate from the infraglenoid tubercle, lateral and posterior humerus surfaces, and posterior humerus, converging to insert at the olecranon of the ulna for powerful extension.

The pronator teres and pronator quadratus are responsible for pronating the forearm at the radioulnar joints. The pronator teres originates from the medial epicondyle of the humerus and coronoid process of the ulna, inserting on the mid-lateral radius. The pronator quadratus originates on the distal ulna shaft and inserts on the distal radius, providing additional pronation force.

The supinator muscle supinates the forearm at the radioulnar joints, rotating the forearm so the palm faces upward. It originates from the lateral epicondyle of the humerus and the ridge near the radial notch of the ulna, inserting on the lateral surface of the proximal one-third of the radius to enable this rotational movement.

The anconeus is a small triangular muscle located at the elbow joint that extends the forearm. It originates from the lateral epicondyle of the humerus and inserts on the olecranon and superior portion of the ulnar shaft, working with the triceps brachii to assist in forearm extension.

Forearm flexors and extensors act on the elbow joint, while pronators and supinators act on the radioulnar joints. Flexors like the biceps brachii and brachialis decrease the angle at the elbow, whereas extensors like the triceps brachii increase it. The pronators and supinators rotate the radius around the ulna, enabling forearm rotation independent of elbow movement.