“It’s perfectly fine to work your abs every day – as long as you mix up your exercises,” Renderer says. “If you do only crunches day after day, without a break, you’ll injure your rectus abdominis and not get the gains you’re looking for.”
Renderer recommends picking three core exercises that work the torso through different plains of motion, such as planks, seated twists, and oblique side-ups. Do these every day for a week and then switch it up. She says it’s fine to incorporate crunches into your routine. Just don’t do them every single day to avoid a repetitive stress injury.