Elbow flexion is mainly performed by which nerve roots and muscles?

• A. C5, C6 - biceps, brachioradialis
• B. C5, C6 - deltoid
• C. C7, C8 - extensor digitorum
• D. C8, T1 - first dorsal interosseous

Answer: (A)

Elbow flexion is driven primarily by two muscles: the biceps brachii and the brachioradialis. Both rely on nerve roots from the C5 to C6 level. The biceps brachii is a major elbow flexor (and also supinates the forearm) and is innervated mainly by the musculocutaneous nerve, which carries C5–C6. The brachioradialis also contributes significantly to elbow flexion, especially when the forearm is in a midpronated position, and it receives innervation from branches of the radial nerve carrying C5–C6. Together, these muscles and roots explain elbow flexion most directly.

The other options point to muscles whose primary actions or nerve supplies are different. The deltoid can assist with shoulder movements and is innervated by the axillary nerve (C5–C6) but not a primary elbow flexor. Extensor digitorum extends the fingers and is innervated mainly by the radial nerve with components around C7–C8. The first dorsal interosseous is a hand muscle innervated by the deep branch of the ulnar nerve (C8–T1) and is unrelated to elbow flexion.