BicepsBiceps Brachii

arms2 musclesMusculus biceps brachii

The biceps brachii is the two-headed muscle on the front of your upper arm. Its strongest job is not bending the elbow — it is turning your palm upward, which is why curl grip changes everything.

Biceps: its 2 muscles highlighted on an anatomical figure, from the front — Long Head and Short Head.
Where the biceps sit, from the front.

The biceps has two heads, both starting on the shoulder blade and joining into one belly that ends in a single tendon at the elbow. The long head starts just above the shoulder socket and its tendon runs through the shoulder joint itself before dropping down a groove on the front of the arm bone; the short head starts on the coracoid process, the small hook of bone at the front of the shoulder blade.

The tendon at the far end does not attach to the bone you would expect. It wraps around the radius — the forearm bone on the thumb side — and attaches to a bump on its inner face. That wrapping is what makes the muscle a supinator: when it shortens, it unwinds the radius and rolls the palm face-up. It is stronger at this than at anything else it does.

It bends the elbow too, but it is not the main elbow flexor and it is not even the biggest one. The brachialis underneath it is the muscle whose only job is bending the elbow, and it does more of the work in most positions. The biceps is at its best as an elbow flexor only when the palm is already supinated.

Because both heads cross the shoulder as well as the elbow, the biceps also assists in raising the arm forward — which is why the position of the elbow relative to the torso changes how a curl feels, and why an incline curl with the elbows behind the body feels harder than a standing one.

Training notes

Grip decides how much of a curl is actually biceps work. A supinated barbell or dumbbell curl gives it the most. A neutral hammer grip shifts the work to the brachialis and brachioradialis. A pronated reverse curl shifts it further still. All three are useful, and doing only the first is training one third of the elbow flexors.

The biceps is also the muscle most likely to steal work from the back. Every row and pulldown bends the elbow, so a lifter who cannot feel their lats is often getting a very effective biceps session out of their back day — which is worth knowing before adding more direct arm volume.

Elbow position is the variable that separates curl variations that actually differ. Elbows in front of the body — a preacher curl — shortens the muscle at the shoulder and makes the bottom of the range harder. Elbows behind the body — an incline curl — lengthens it and makes the stretch position the hard part. Both are worth having; a standing curl sits between them.

Because supination is its strongest action, finishing a dumbbell curl by deliberately rotating the palm further upward at the top gives the muscle a job it otherwise never gets in the gym. It is a small addition and one of the few genuinely biceps-specific things available.

Anatomy

Origin
  • Long head: supraglenoid tubercle of the scapula
  • Short head: apex of the coracoid process of the scapula
Insertion
  • Radial tuberosity
  • Deep fascia on the medial side of the forearm, through the bicipital aponeurosis
Actions
  • Supinates the forearm, turning the palm upward — its strongest action
  • Flexes the elbow, most powerfully when the palm is already facing up
  • Assists flexion of the arm at the shoulder
Innervation
Musculocutaneous nerve (C5–C6)

Parts of this muscle

Exercises

Antagonists

Synergists