You’ll feel this exercise more in the abdominal muscles — and less in the hip flexors — by gripping a roller with the backs of your thighs. That’s because recruiting the backs of your legs will prevent you from overworking the front of your legs and hips. The result is an intense workout for your abs.
Lie on a mat or a padded surface. Cross your ankles and hug a 36-inch roller by squeezing your heels toward your hips. (Hold the roller behind your ankles, not behind your knees.) Place your hands behind your head. Inhale.
On an exhale, contract your abdominals and, without dropping the roller, raise your tailbone and hips slightly off the floor. Simultaneously roll your head, shoulders and upper back off the floor, moving your body into a tight ball. Pause at the peak of the contraction, then slowly release down to the starting position. Repeat 12 to 16 times. Rest, change the cross of your legs and repeat for another set.
Source : Los Angeles Times