Muscles that cross the Elbow Joint; Movements of Forearm

Brachialis

Strong muscle immediately deep to biceps brachii on distal humerus. Origin is front of distal humerus, around deltoid tuberosity. Insertion is into coronoid process of ulna. Major forearm flexor

Triceps brachii

Large fleshy muscle, three-headed origin. Long and lateral heads lie superficial to medial head. Long head origin is on scapula, lateral head origin is posterior shaft of humerus, medial head origin is posterior shaft of humerus. Insertion is by common tendon into olecranon process of ulna. Prime mover of forearm extension, long head also stabilizes scapula and assists in arm adduction.

Sidenote

Muscles fleshing out the arm cross the elbow joint to insert on the forearm bones. Since the elbow is a hinge joint, movements promoted by these muscles are limited almost entirely to flexion and extension of the forearm. Walls of fascia divide the arm into two muscle compartments; the posterior extensors and the anterior flexors. The prime mover of forearm extension is triceps brachii which forms most of the posterior compartment. All anterior arm muscles cause elbow flexion. These are the brachialis, biceps brachii, and brachioradialis. The brachialis and biceps brachii insert, respectively, into the ulna and radius and contract simultaneously during forearm flexion. The biceps brachii muscle also causes supination of the forearm—the forearm must stay supinate for maximal force from this muscle. This is why doing chin-ups is much harder in the pronate position. The brachioradialis originates on the distal humerus and inserts on the distal radius, so most of its mass lies in the forearm. Therefore, it is a weak forearm flexor that only becomes active when the forearm is already partially flexed and semipronated.

Brachioradialis

Superficial muscle of lateral forearm. Originates from distal end of humerus, inserts at base of styloid process of radius. Synergist in forearm flexion, acts best when forearm is already partially flexed and semipronated

Biceps brachii

Two-headed fusiform muscle, bellies unit as insertion point is approached. Short head origin is coracoid process of scapula; long head origin is around glenoid cavity. Insertion is by common tendon into radial tuberosity of radius. Produces forearm flexion and forearm supination. These actions often occur at the same time, as when you open a bottle—it turns the corkscrew and pulls the cork. Because it also crosses the shoulder joint, it can act as a weak arm flexor.