Three kinds of muscle

Some muscles move when you tell them, and some work all by themselves, like the ones in your tummy.

A muscle is bundles inside bundles, all the way down to tiny threads that slide. Underneath are your three kinds of muscle. Press Squeeze, or tap any part!

Skeletal muscle: you're the boss

Skeletal muscles are tied to your skeleton, which is all your bones. They're the ones that move you around.

You choose when they move. You decide to kick, wave or jump, and they do it. Scientists call this voluntary (VOL-un-tair-ee), which means 'you choose.'

Under a microscope, skeletal muscle has light and dark stripes, a little like a zebra. Scientists call it striated, which means striped.

Try it: wiggle your toes. You decided, and your skeletal muscles did the wiggling.

Smooth muscle: works on its own

Smooth muscle has no stripes. It's found in the walls of your stomach, your intestines, your bladder and your blood vessels.

It works without you thinking about it. Scientists call this involuntary, which means 'it works on its own.'

Smooth muscle moves slowly, in waves. In your intestines, it squeezes food along, a bit like squeezing toothpaste through a tube.

Tiny smooth muscles in your skin pull your little hairs up straight when you're cold. That makes goosebumps! Smooth muscles in your eyes also make your pupils, the dark dots in the middle, bigger or smaller.

Cardiac muscle: the heart's own kind

Cardiac (KAR-dee-ak) means 'of the heart.' This kind of muscle is found only in your heart.

It has stripes like skeletal muscle, but you can't control it. It keeps its own beat, about 100,000 times a day.

It doesn't get tired the way your legs do after a long run. It rests for a tiny moment between every beat, then goes again, for your whole life.

Try it: put two fingers on the side of your neck, just under your jaw. Feel the thump, thump? That's cardiac muscle at work.

You choose, or it chooses?

Here's a quick way to sort them. If you can move it when you want, like your fingers, legs or tongue, it's skeletal.

If it works all by itself, like your stomach or your heart, it's smooth or cardiac.

A few muscles can do both! Your diaphragm, the breathing muscle, works on its own while you sleep. But you can also take a big breath or hold your breath on purpose. Your eyelids blink on their own too, and you can still wink when you want.

A team inside you

All three kinds work together all day. Think about eating lunch.

Your skeletal muscles lift the sandwich, chew it and start the swallow. Then smooth muscle takes over and squeezes the food down to your stomach and through your intestines.

And the whole time, cardiac muscle in your heart pumps blood to all those other muscles so they have energy.

🤩 Wow facts

Your heart muscle beats about 100,000 times a day, and it never takes a day off.
Skeletal muscle looks striped under a microscope, and smooth muscle does not.
Smooth muscle in your intestines squeezes in slow waves to push food along.
Goosebumps come from tiny smooth muscles that pull your little hairs up straight.
The muscles that make your pupils grow bigger in the dark are smooth muscles that work on their own.
Your diaphragm is a skeletal muscle, yet it keeps you breathing all night while you sleep.
Myth: All muscles are the kind you can control. Truth: The muscles inside your organs work on their own, without you thinking about them.

💚 Look after it

Move your skeletal muscles every day by playing.
Running, jumping and dancing make your heart work hard, which helps keep it strong.
Eat fruits, veggies and whole grains, and drink water. They help the smooth muscle in your intestines keep food moving.
Sleep well. Your heart and breathing muscles keep working, and the rest of you gets to recharge.

🩹 When something goes wrong

Tummy cramps. Sometimes the smooth muscle in your belly squeezes hard, and it hurts. Often it goes away soon. If a tummy ache is strong or won't stop, tell a grown-up.

🙋 Questions kids ask

Can I make my heart stop or start?

No. Your heart keeps its own beat, all by itself. Running makes it beat faster, and resting slows it down.

Which kind of muscle is my tongue?

Skeletal muscle. You choose how to move it, which is why you can stick it out or wiggle it.

Why can't I feel my stomach muscles squeezing?

Smooth muscle works slowly and quietly. Sometimes you can hear it, though: that rumbly tummy sound is food, air and juices moving along.

🧠 Quick quiz

Question 1 of 3Which kind of muscle is found only in your heart?

🔊 Skeletal muscle: you're the boss

🔊 Smooth muscle: works on its own

🔊 Cardiac muscle: the heart's own kind

🔊 You choose, or it chooses?

🔊 A team inside you