Right now, bend your arm and touch your shoulder. Then straighten it out. You just used your muscles — the amazing pulling helpers hidden inside your arm!
In this lesson you will discover:
Muscles PULL They work in pairs Meet the biceps & tricepsTap Next when you're ready to look inside your arm. 🔎
Here is the big secret: a muscle can squeeze shorter to pull, but it can never push. Think of it like a rope — you can pull a wagon with a rope, but you can't push a wagon with one!
Squeeze the muscle and watch it get shorter and fatter:
The biceps is the muscle on the front of your upper arm. When it contracts (squeezes shorter), it pulls your forearm up and your arm bends.
Biceps: relaxed — arm is straight.
Slide it all the way to Bent to make the biceps do its job!
The biceps pulled your arm up. But a muscle can't push it back down! So there is a second muscle at the back of your upper arm called the triceps. When the triceps contracts, it pulls your arm straight again.
Which muscle straightens a bent arm? Tap your answer:
Your biceps and triceps are a pair. They take turns: while one contracts, the other relaxes. Press the buttons and watch both muscles switch jobs!
Try a button!
Drag each word into the right box to finish the sentence. Give it a try — you can always drag a word back!
To bend the arm, the ? contracts. To straighten it, the ? contracts.
Tip: on a tablet, tap a word then tap a box. 👆
Your body is full of muscle pairs that take turns pulling. They move your legs when you run, your fingers when you write, and even help you smile!
Guess: what do your muscles need to keep working well? Tap all the good ideas!
You now know how muscles move your arm. Here's the whole story:
Next time you wave hello, remember your biceps and triceps are teaming up! 👋