Three heads
Tri means three. The triceps has three heads at the top: one ties onto your shoulder blade, and two tie onto your upper arm bone.
All three join into one strong tendon at the bottom. It ties onto the pointy tip of your elbow.
Try it: feel the pointy bone at the back of your elbow. That's where your triceps holds on.
Straighten up
Try it: bend your elbow. Put your other hand on the back of your upper arm, then straighten your arm all the way. Feel it get firm? That's your triceps pulling.
Your triceps works when you push a door open, give a high five, reach up to a high shelf or throw a ball.
It also helps when you push yourself up out of a chair.
Bigger than the biceps
Everyone talks about the biceps, but the triceps is bigger. It makes up about two thirds of the muscle in your upper arm.
It's on the back of your arm, so you can't see it easily in a mirror. That's probably why it gets less attention.
A team of opposites
The biceps bends your elbow, and the triceps straightens it. While one pulls, the other relaxes.
Your brain takes care of the timing, so you never have to think about it.
Even when you hold a cup of water still, both muscles pull a little at the same time. That keeps your arm steady so you don't spill.