The key to bodyweight exercise is mixing it up. Challenge yourself. If you're not sore the next day, you didn't work out hard enough. "When you push yourself, you'll be building muscle, increasing bone density, strengthening ligaments, and burning calories for up to 36 hours after your workout," says Mark Lauren, author of 'You Are Your Own Gym.' When push-ups become too easy, switch to a different grip – wide, narrow, or staggered hands – or pause during the motion. Try one set on an incline, the next on a decline, and the next with one hand on a basketball. For all of the exercises below, aim for three sets of 10 reps unless noted otherwise. Time yourself and try to do them more quickly the next time around. If you can't finish a set, complete it with the easier version.
The No-Weights Workout: Mountain Climbers
From push-up position, bring one knee to your chest and back; repeat with the other knee. Try to do 25 on each side.
Make it Hard
Lift your knee up and across your chest, toward your opposite shoulder. This works more of your oblique muscles.
Credit: Photograph by John Loomis
From push-up position, with your feet flat against a wall, do mountain climbers.