This article was originally published on October 5, 2015.

Here’s the thing about abs: Whether you care about getting ripped or not, your core goes way beyond those six-pack muscles in both form and function. The muscles of your mid-torso — the ones on your back, sides, and underneath the more superficial rectus abdominis muscles — are the support system for your spine. Translation: They’re the foundation for almost all movement, in and out of the gym. “Strong core muscles assist in everything you do physically, in ways that would surprise you, from lifting a box over your head, to pulling a suitcase, to twisting your body while parking your car,” says Luci Gabel, an exercise physiologist and fitness coach and founder of LuciFit. Because they're so essential, when abs and back muscles are weak, it can cause all kinds of trouble: bad posture, back pain, and even spinal injury, Gabel says.

That’s the main reason you won’t see a single crunch during these 30 days. It’s not that crunches are bad, but they really only activate those front six-pack muscles. “Since the abdominal muscles' main function in life is to hold the core stable, it’s important to train them to work with the back in ‘stability mode,’ so they do their job well,” Gabel says. In other words, you want to train your core muscles to resist movement, rather than give in to it.

By having you slowly move your limbs in ways that challenge the core to hold strong and balanced, the four exercises here do just that. “When we extend an arm or a leg, it becomes harder to hold the body in place,” says Gabel. “This is very functional training, since in life, sometimes we work our arms and legs in parallel and sometimes we don’t.” The key word is “slowly” — you’ll notice that the rep counts are very low, maxing out at 6. That’s because you should be taking your time with each movement (quite a bit more time than the GIFs below might suggest!).

Take a 30- to 60-second rest between sets (denoted with a “x2”) before beginning again. On days that include more than one exercise (denoted with a +), move from one exercise to the next without much of a break.

Read on for the calendar in full and for more detailed instructions on how to do each exercise.