Action:  Elbow flexion

Nerve:  Musculocutaneous

Compartment:  Anterior of the arm

Skeletal muscle:  Brachialis and biceps brachii

Cutaneous distribution:  Lateral forearm

Neuromuscular deficit:  Weakness/paralysis when flexing at the elbow under resistance. Flexion with the forearm in the pronated position assesses the functional integrity of the brachialis. However, flexing the elbow with a supinated forearm evaluates both the brachialis and biceps brachii. Denervation is accompanied by muscular atrophy, extension of the elbow, and deficit along the cutaneous distribution of the musculocutaneous (lateral antebrachial cutaneous) nerve.

Differential diagnosis: Recall that activation of the radial nerve/brachioradialis provokes elbow flexion when the upper limb is in the carrying position. Flexor weakness/paralysis plus cutaneous deficit along the posterior arm and forearm indicates radial nerve impairment, while cutaneous deficit that includes the lateral forearm is diagnostic of musculocutaneous nerve dysfunction.