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 Sit on a padded surface or a mat, with the roller positioned behind your mid-back (it should end up just below your shoulder blades). Put your feet flat on the floor; place your hands behind your head with your elbows pointed to the sides.

2 Keeping your head supported with your hands, slowly lower your head, neck and shoulders to the floor while slightly arching your back over the roller. On an exhale, contract your abdominal muscles and curl your upper body forward. Focus on compressing your navel in toward your spine. Pause for two seconds, holding the peak of the curl. Do 12 to 16 reps, rest for 20 seconds and repeat.

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.