Finding it hard to fit in fitness? Just getting through a day of school and after-school commitments can leave most of us wondering where to find time — and if all the running around we do counts as exercise. (It does. But if it's the only exercise we get, it's usually not enough.)

What more should we do? First, try to make sure aerobic activity adds up to more than 60 minutes a day. Aerobic activity is anything that gets your heart going — like biking, dancing, or running. Then take a few minutes for some strength training. Exercises like the ones below help build muscle to boost metabolism and keep joints working well. Flexibility is the third component of well-rounded exercise. Check out yoga as one way to stay flexible.

You can do these three strength-building exercises at home. There's no need for special equipment, expensive gym fees, or lots of time. Just check with your doctor, PE teacher, or coach first to be sure these exercises are OK for you.