Add an extra challenge to classic push-ups by performing them on the unstable surface of a foam roller. Begin doing them on your knees until you develop the necessary strength to do straight-leg push-ups.

1 Kneel on a padded surface or on a mat. Place your hands shoulder-width apart on a foam roller. Position the roller so that your wrists are directly below your shoulders (make sure you have your thumbs on top of the roller, close to your fingers). Pull your abdominals in toward your spine and keep your shoulders relaxed, down away from your ears. Lift your feet and balance on your hands and knees.

2 Inhale while you slowly bend your elbows, pointing them back toward your feet. Pause for two seconds with your elbows at shoulder height. On an exhale, push down on the roller as you slowly straighten your arms, pushing straight up. Do not allow the roller to move throughout the entire exercise. Repeat 8 to 12 times.

This article originally appeared in the Los Angeles Times in the "Good Form" feature of the Health Section. "Good Form" is updated with a new Karen Voight article each Monday.