Biceps brachii

The showpiece muscle on the front of the arm. It bends the elbow and, uniquely, turns the palm up (supination) — its role in twisting a screwdriver is as important as curling a weight.

This muscle in 3D

Drag to rotate · scroll to zoom — see the shape, origin and insertion of the biceps brachii. 3D model via Sketchfab (CC-BY).

Anatomy

Muscles: Biceps brachii (long & short heads), with brachialis underneath

Origin: Long head: supraglenoid tubercle of the scapula (runs through the shoulder). Short head: coracoid process of the scapula.

Insertion: Radial tuberosity of the forearm (and bicipital aponeurosis).

Actions:

Elbow flexion
Forearm supination (palm-up rotation)
Weak assist in shoulder flexion

How the muscle works

Because it crosses both the shoulder and elbow, it is a two-joint muscle. It generates most force as an elbow flexor when the forearm is supinated; the deeper brachialis flexes the elbow regardless of grip.

Fibre-type bias: Mixed, slightly fast-twitch — responds to both heavier low-rep and moderate-rep work.

Functional role: Pulling, lifting and carrying; controlling palm rotation.

Common problems

Biceps tendinopathy (front of shoulder)
Long-head tendon tears (the 'Popeye' bulge)
Distal (elbow) tendon rupture

Training & stretching

Curls (barbell, dumbbell, incline), chin-ups, hammer curls (brachialis/brachioradialis).

Arm extended and externally rotated against a wall; doorway stretch.