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beginnerSource-checked11 min read

The Arms: An Overview

The biceps and triceps opposing pair, plus their quieter helpers brachialis and coracobrachialis.

Before this: Fundamental Movement Terms

You will be able to

  • Name the four arm muscles and their primary actions.
  • Explain the opposing relationship between the biceps brachii and triceps brachii at the elbow.
  • Distinguish the brachialis's 'pure' elbow flexion from the biceps's dual flexion/supination role.
Simplified side view of the upper arm showing the two-headed biceps brachii on the front of the humerus and the three-headed triceps brachii covering the back of the humerus, down to the elbow.
Arms — biceps brachii and triceps brachii (simplified). A beginner-level schematic of the upper arm's opposing muscle pair: biceps brachii and triceps brachii.
Illustration: Anatomy Learning Platform (original) · CC0-1.0 (public domain dedication)

⚠ Safety note

Sudden sharp pain, a popping sensation, or visible deformity in the upper arm needs prompt medical evaluation. A trainer coaches curl and extension technique; they do not diagnose tendon injuries.

An opposing pair, plus two helpers

The upper arm is built around a classic opposing pair at the elbow:

  • Biceps brachii (front) — flexes the elbow and is also the body's strongest forearm supinator.
  • Triceps brachii (back) — extends the elbow, and makes up more of the upper arm's bulk than the

biceps.

Two smaller muscles round out the region: the brachialis, a deep, 'pure' elbow flexor unaffected by forearm rotation, and the coracobrachialis, which — despite living in the arm — only acts at the shoulder, not the elbow.

Grip changes emphasis

Because the biceps is both a flexor and a supinator, forearm rotation changes how much it contributes to a curl. A palm-up curl favors the biceps; a neutral-grip hammer curl shifts more work to the brachialis, which doesn't care which way the palm faces.

Sources for this lesson

“The biceps brachii flexes the elbow and supinates the forearm; the triceps brachii extends the elbow; the brachialis flexes the elbow independent of forearm rotation.”

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

Take the quiz (4 questions)Explore the Arms

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