I started taking Pilates classes three years ago. The impetus came when I tried to pick up my roommate’s cat, felt a stab of pain in my lower back, and couldn’t walk for 24 hours. (To be fair, the cat was chubby.)

I was fine after a few days, but I decided that I needed to take up a back-strengthening type of exercise. The problem was, I’ve never been particularly fit. I struggled to bench press the unweighted bar in high school PE, I still have nightmares about the mile run, and, if you recall, I threw my back out at age 22.

But I went to Pilates anyway. Then, I actually kept going. I’m proud to say that over the past three years, I’ve gotten a lot stronger, and I’ve also learned some interesting facts about exercise and the body. For example:

1. Spines aren't like pillars. They're curvy and alive.

Everyone has a natural curve in their lower back. If you lie down casually on a Pilates mat, without pushing your spine into the mat, there’s a gap between your back and the ground—yes, even for people with good posture who “sit up straight.”

Spines are bendy, too. Anyone who’s picked something up off the floor knows that, but you really feel it during exercises like the rollup. A lot of teachers, during that movement, tell you to peel your spine off the floor “one vertebra at a time,” or to pretend that you’re wearing a striped shirt and rolling up stripe by stripe. That move in particular makes me conscious of how the spine really works.

2. There are bones in your butt.

They’re called “sitz bones,” and they’re little nubs that stick out of your pelvis. In a more accurate world, they would be called butt antlers. They’re not usually noticeable, as they’re completely covered by booty flesh.

That doesn’t mean you can’t find them, though. My Pilates teachers have taught me that when you sit up straight, all of your weight sits on top of your sitz bones, and you can feel them pressing into the floor a little. It’s not uncomfortable, but it is a reminder that your skeleton is full of surprises.

3. Just thinking about your pelvis can improve your alignment ... and creep you out.

When you’re lying down, Pilates teachers tell you to think of your pelvis like a bowl. When you tilt it forward, you’re spilling the bowl’s contents towards your feet. (This feels like sticking your butt out.) When you’re tilting it backwards, the bowl spills towards your face. (This feels like pushing your lower back into the ground.) “Neutral pelvis” is the place halfway in between, and feels roughly effortless. Just thinking about my pelvis in these terms has improved my posture.

It also freaks me out a little. Sometimes, I look in the mirror and think, “There’s a pelvis inside of me.” This may be a personal problem.

4. Toning your whole core takes more than sit-ups.

When I first started Pilates, the movements felt crazy. There’s a lot of lying on your side, waving your legs around, and holding one-legged bridge poses. I missed sit-ups. You can’t fall over during a sit-up, and I was unsure what these weird exercises did that sit-ups didn’t.

The thing is, Pilates isn’t just supposed to make your abs look six-pack-y. It’s meant to strengthen your whole core—your back muscles, your upper and lower abs, and your obliques. Basically, any muscle in the middle of the body that stabilizes you when you fall (or lean over really far on purpose). Accessing all these muscle groups requires some weird motions.

5. Your body can learn ... but it can't learn everything.

Until I took Pilates, I never appreciated the fact that my body can learn things just like my brain. For instance, there’s an exercise called The Hundred. It looks like this:

It’s a staple—you’d be hard-pressed to find a Pilates class that skips this one—and at first, my face turned purple doing the beginners’ modification with bent knees. I couldn’t imagine doing the advanced version with extended legs. And then, slowly, over time … I worked up to it. I felt like I had developed a superpower.

There are some things I still can’t do, though. Like sit up straight, with my legs straight out in front of me. Nope! I can only sit up straight when I’m cross-legged, and at this point, I’m pretty sure it’s just how my body is wired. As my Pilates teachers say soothingly at almost every class, “Everyone’s body is different.”

Read more about bendy exercise trends:

Five Reasons Not to Fear the Pilates Reformer

It might look like it's going to hurt you, but it just wants to build your core strength.

Yes, Yoga is a Sport

And Gianna Purcell is the reigning champion. Here’s how she worked her way to the top.