Kids are always being told to stop eating junk food and do more exercise, and now it seems more and more of you are heading to the gym to get fit.
In the last three years, the number of kids in Britain who are members of gyms has risen by nearly 40%.
Some schools are even buying up specially-designed equipment so that kids can work out at school too.
But joining a gym can be really expensive, and experts say doing other types of exercise is just as good.
More and more people in Britain are becoming worryingly overweight.
It's thought by 2010, one in four children could be clinically obese - meaning they are dangerously overweight.
Plastic weights are used for kids because they're safer
Experts want kids to cut down on junk food, and the amount of time they spend doing things like watching TV and using the computer.
Instead, they want them to try and eat healthily and get more exercise.
Hitting your local gym and sweating it out on a treadmill will help get you fitter.
But running around a park or playing football with your mates are also good ways to keep fit, and don't cost a penny.