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Biceps brachii
The front-of-arm muscle that bends the elbow and, more importantly, turns the palm upward.
Latin name: Musculus biceps brachii. In plain English, the two-headed muscle at the front of the upper arm. It is filed here under arm and forearm.
Reference information, not a diagnosis. Where a symptom is described below, it is there so you can describe your own more precisely to a clinician — not so you can name what you have.
Where it is
The biceps has two heads, as the name says, and neither of them attaches to the upper arm bone. Both come from the shoulder blade: the long head from a small bump above the socket, its tendon running through the shoulder joint itself and down a groove in the front of the humerus, and the short head from the hook of bone called the coracoid process. They join into one belly and one tendon that turns to attach on the radius, the forearm bone on the thumb side.
That insertion point is the key to the muscle. Because the tendon wraps around the radius, contracting the biceps does not just bend the elbow — it rolls the forearm over, turning the palm up. A flat sheet of connective tissue, the bicipital aponeurosis, also spreads from the tendon across the front of the forearm, spreading some of the load into the fascia rather than all of it into one bony point.
| Feature | Detail |
|---|---|
| Origin | Long head from the supraglenoid tubercle of the scapula, running through the shoulder joint; short head from the coracoid process |
| Insertion | Radial tuberosity, with the bicipital aponeurosis spreading into the fascia of the forearm |
| Nerve | Musculocutaneous nerve (C5-C6) |
| Main actions | Supination of the forearm, flexion of the elbow, and weak flexion of the shoulder |
What it does
Supination is the biceps' strongest action, and it is strongest with the elbow bent to a right angle. This is why a right-handed screw thread tightens with a supinating motion: it was designed around the fact that the human forearm is stronger turning clockwise from that position. Elbow flexion is shared with brachialis, which sits underneath and does not care which way the palm faces, and with brachioradialis in the forearm.
The long head crosses the shoulder as well, so it assists shoulder flexion weakly and helps stabilise the head of the humerus. That extra role is also its weakness: the tendon runs through a tight groove and over the top of the joint, and it is a common source of front-of-shoulder pain in people who lift or throw a lot.
Exercises that load it
| Exercise | Category | Muscles the exercise library lists |
|---|---|---|
| Pull-ups | Strength | Lats, biceps, mid-back, grip |
| Bent-over row | Strength | Mid-back, lats, biceps |
| Rowing machine | Cardio | Legs, back, arms, heart |
| Farmer's carry | Strength | Grip, core, upper back, legs |
Any pulling movement loads the biceps whether or not you are trying to. Pull-ups with the palms facing you put it in a strong position; rows load it through a long range with the shoulder moving as well. Direct curls load supination and elbow flexion together if you finish each rep with the palm fully turned up. The muscle is small, recovers quickly and rarely needs the volume people give it.
How it is lengthened
Extend the elbow fully, turn the palm down and take the arm slightly behind the body — for example with the hand on a wall behind you, then turning your body away. That combination lengthens all three of its actions at once. Go gently: the same position stresses the front of the shoulder capsule and the long head tendon, which are exactly the structures that ache in people who need the stretch.
When it goes wrong
| Problem | What it typically feels like | Usual setting |
|---|---|---|
| Long head tendinopathy | A localised ache at the front of the shoulder, tender in the groove, worse lifting or reaching forward | Repetitive overhead or pulling load, often alongside rotator cuff irritation |
| Proximal tendon rupture | A sudden pop at the shoulder with bruising and a bunched-up muscle belly lower in the arm | A heavy eccentric load in an arm with pre-existing tendon degeneration, usually in mid-life or later |
| Distal tendon rupture | A sudden painful tearing at the elbow crease with marked weakness turning the palm up | A heavy load taken on a bent arm being forced straight, such as catching a falling weight |
A sudden pop with visible change in the shape of the arm, bruising, and weakness turning the palm up should be assessed promptly — a torn distal biceps tendon is time-sensitive and the decision belongs to a clinician.
Nothing on this page is a treatment plan. If a problem is limiting what you do, is not improving, or is getting worse, the right next step is an assessment by a doctor or a physiotherapist who can examine you.
Sources: descriptive anatomy from Gray's Anatomy of the Human Body, 20th US edition (1918), which is in the public domain; Latin names follow Terminologia Anatomica, published by the Federative International Programme for Anatomical Terminology. Nerve root levels are the conventional ranges taught from those sources and vary between individuals and between textbooks. Exercise cross-links use the TempoLife exercise library. Checked 2026-09-06.
Frequently asked questions
Is the biceps the main elbow flexor?
Not on its own. Brachialis, lying underneath, is the workhorse of elbow flexion and works regardless of forearm position; brachioradialis contributes too. The biceps is the strongest supinator, which is its more distinctive role.
Why does my front shoulder hurt when I do curls?
Because the long head of the biceps runs through the shoulder joint and along a groove at the front of the arm bone. Load applied at the elbow is transmitted straight to that tendon. Front-of-shoulder pain with pulling and curling is a common pattern and worth having looked at if it persists.
Does a "Popeye" bulge need surgery?
That is a clinical decision, not a website one. A change in the shape of the muscle after a sudden pop means a tendon has gone, and which one it is changes the answer completely. Get it examined.
Nearby in this reference
Triceps brachii
The three-headed muscle at the back of the upper arm
Forearm and grip
The muscles below the elbow that close your hand
Deltoid
The cap of the shoulder
Rotator cuff
The four small muscles that hold the shoulder in its socket
Trapezius
The big diamond across the upper back and neck
Rhomboids
The straps that pull the shoulder blades together
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