Update this popular abdominal exercise by performing it on a foam roller. You'll train multiple core muscles at the same time with one simple move.

1 Lie face up on a full-length, round foam roller with your head and hips supported on the roller. Place your hands on the floor with your palms down. Start with your knees bent above your hips at a 90-degree angle. Focus on keeping your abdominal muscles pulled in toward your spine. Straighten your right leg out in front of you. Pause for two seconds.

2 Now switch legs by bending your right leg and extending your left leg in front of you. Pause for two seconds, making sure your midsection stays flat. Continue alternating sides until you have done 30 reps (15 on each leg).

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.