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Brachialis

Pronunciation: bray-kee-AL-iss

For beginners

Hidden underneath the biceps, this muscle also bends your elbow — but unlike the biceps, it works just as hard no matter which way your palm is facing.

Show the advanced explanation

Because it inserts on the ulna (not the radius) and does not cross the radioulnar joint, its force output does not change with forearm rotation, making it a consistent contributor across all curl grip variations.

Structure & function

Location: A muscle lying deep beneath the biceps brachii, on the front of the lower half of the upper arm.
Origin: Lower half of the front of the humerus.
Insertion: Coronoid process of the ulna.
Main action(s): Flexes the elbow; unlike the biceps, it does not cross the shoulder or contribute to supination, making it a 'pure' elbow flexor.
Joint(s) crossed: Elbow joint only
Movement plane: sagittal
Innervation: Musculocutaneous nerve (C5–C6)
In daily movement: Contributes to every elbow-bending task, working alongside the biceps regardless of forearm rotation.
In exercise: A major contributor to elbow flexion in all grip positions, and the primary target of neutral-grip (hammer) curls.
Commonly confused with: Frequently not distinguished from the biceps at all, despite being a separate muscle with a meaningfully different mechanical role.
Common misconceptions: 'Only the biceps grows from curls' ignores the brachialis, which sits beneath the biceps and can add to overall arm thickness.

Exercises that use this muscle

As a primary mover

Hammer Curl

As a secondary / stabilizer

Barbell Bicep Curl (secondary)
Isometric Elbow Flexion Hold (secondary)

⚠ Safety note

Same general precautions as other elbow flexors — assess sudden sharp pain rather than training through it.

Sources

“The brachialis flexes the elbow and, unlike the biceps brachii, does not act on the shoulder or radioulnar joints.”

Anatomy and Physiology 2e — OpenStax, Rice University · Ch. 11.5 Muscles of the Pectoral Girdle and Upper Limbs

Peer-reviewed textbook · License: CC BY-NC-SA 4.0 · Last checked 2026-07-19

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