Okay kiddo, so you know how sometimes when you're playing outside you run really fast and then you slow down and walk for a little bit and then maybe you run fast again? Well, that's kind of what fartlek is! Fartlek is a way of exercising where you run or jog at different speeds and intensities.
So, imagine you're running in a big park. Usually when you go for a run, you might just run at the same speed the whole time. With fartlek, you're going to mix it up! You might start out by running really fast for a little bit, then slow down to a jog, and then speed up again. You can do this for as long or as little as you want!
The really cool thing about fartlek is that you get to decide when to speed up or slow down. If you see a tree that you want to run to, you can sprint to it! If you get tired, you can slow down to a walk. It's all up to you!
Fartlek is a great way to exercise and have fun at the same time. So next time you're playing outside, try fartlek-ing instead of just running at the same speed the whole time!