"The next day, it hurts to even laugh."

Credit: Getty Images

Kendall Jenner has an unbelievably toned tummy, but it's not all good genes: The supermodel has to work really hard for that tight core, as she revealed in a new post on her app.

"My abs are my favorite thing to work out," she says. And boy does it show. The social media maven regularly bares her middle on the runway, and serves up a stream of ab inspiration on Instagram.

Like this:

And this:

"I love it when my trainer, Gunnar Peterson, kills my abs. The next day, it hurts to even laugh. That's how I know I'm doing the exercises right!" she says. (Peterson also works with Jenner's big sis Khloé Kardashian.)

But you don’t necessarily need a celeb trainer to get Kendall-level results. The reality star says she also uses apps like Instant Abs Trainer, which is loaded with different workouts you can do anytime, anywhere.

And one last tip that's totally stealable: "Sometimes when I'm watching TV, I think to myself, 'I should be doing crunches and situps right now.' Then I get off the couch and do it," writes Jenner. Now that's a type of multitasking we can get behind.

Want to make your own ab magic happen? Try this five-move circuit from Emily Skye that you can do on your living room floor. All you need is a mat.

Do each move for 30 seconds. Then rest for a minute, and repeat the circuit five more times to sculpt a rock-hard core.