If you use the ab roller like this, your abs are not being trained at all. 
Instead, first move into something called posterior pelvic tilt by rotating your hips and contracting your abs. Roll out only as far as you can while maintaining this position.
Then, on the way back, don’t just swing your hips back. Instead, think about pulling up with your mid-section to roll back in.
Make these tweaks and you’ll instantly feel the difference.
Take my 60-second quiz to find the right program for you to build muscle and lose muscle—all backed by science:
source