The Body

Grown-ups

Biceps

Biceps brachii, said BY-seps BRAY-kee-eye

Your biceps is the bump on the front of your arm that bends your elbow.

Muscles can only pull. The biceps on top bends your elbow and the triceps underneath straightens it. Press Flex, or tap any part!

Make a muscle!

Bend your elbow and squeeze your fist. See the bump on the front of your upper arm? That's your biceps.

When it squeezes, it gets shorter and fatter, so it bulges up.

Now let your arm hang down and relax. Your biceps gets long and soft again.

Two heads

Biceps means 'two heads' in Latin. Brachii (BRAY-kee-eye) means 'of the arm.' So its full name means 'the two-headed arm muscle.'

At the top, the muscle splits into two ends, called heads. Both tie onto your shoulder blade.

At the bottom, a strong tendon ties it to a bone in your forearm.

Try it: bend your elbow a little and feel the inside of your elbow crease. Feel a hard cord? That's your biceps tendon.

Bending and turning

Your biceps has two jobs. It bends your elbow, and it turns your forearm so your palm faces up, like holding a bowl of soup.

Try it: bend your elbow with your palm facing down. Put your other hand on your biceps, then turn your palm up. Feel it tighten?

Here's a secret: a hidden muscle called the brachialis (BRAY-kee-AL-is) lies under the biceps. It does a lot of the elbow bending too. The biceps just gets most of the credit!

Partners: biceps and triceps

Muscles can only pull. So your biceps needs a partner to straighten your arm again.

That partner is the triceps, on the back of your upper arm. The biceps pulls your forearm up, and the triceps pulls it back down.

When one pulls, the other relaxes and lets go. They take turns, like two kids on a seesaw.

Try it: hold your upper arm with your other hand. Bend and straighten your elbow. Feel the front get hard, then the back?

Everyday biceps

Your biceps helps you carry a lunch tray, pick up your backpack, brush your teeth and pull yourself up on the monkey bars.

Every spoonful of cereal you lift to your mouth is a tiny biceps workout!

🤩 Wow facts

  • Biceps means 'two heads,' because its top end splits in two.
  • The biceps doesn't just bend your elbow. It also turns your palm to face up.
  • A muscle under the biceps, called the brachialis, does a lot of the elbow bending too.
  • Your biceps crosses two joints: your shoulder and your elbow.
  • Myth: The biceps is the biggest muscle in your arm. Truth: The triceps on the back of your arm is bigger.
  • Biceps is the name for just one muscle, even with an s on the end. The s is part of its Latin name.

💚 Look after it

  • Climb, swing on the monkey bars and carry your own backpack to keep your arms strong.
  • Lift things by bending your knees and holding them close, so your arms and legs share the work.
  • Rest your arms when they feel shaky and tired.

🩹 When something goes wrong

Tired, shaky arms. After lots of climbing or carrying, your arms can feel shaky. That just means they worked hard. Rest and drink some water. If your arm really hurts or looks puffy, tell a grown-up.

🙋 Questions kids ask

Why does my biceps bulge when I flex?

When a muscle squeezes, it gets shorter and fatter, so it pops up like a bump.

Is it 'bicep' or 'biceps'?

Scientists say 'biceps' even for one, because the s is part of the Latin name. Lots of people say 'bicep,' though.

Can I watch my biceps work?

Yes! Bend your elbow and squeeze your fist, then watch the bump grow on the front of your arm.

🧠 Quick quiz

Question 1 of 3What does 'biceps' mean?

🔗 It works with

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