There’s something about what happens when you crack your back that’s so unbelievably satisfying. Whether it accidentally snaps and crackles when you stand up or you whip out your best contortionist moves to make it happen, that little pop just feels damn good. If this describes you to a T, you’ve probably been cracking your back for years with no idea as to what, exactly, happens inside your body when you do it.

Clearly nothing is actually breaking, or cracking your back would seriously hurt and be nowhere near as popular as it is. “Cracking your back is very common,” Ferhan Asghar, M.D., assistant professor of orthopedic surgery at UC Health, tells SELF. But what actually produces that resulting noise and feeling of relief? Oddly enough, what’s really happening when you crack your back is up for some debate (more on that shortly). What’s not up for debate is how damn good it feels. So, let’s dive in to all things back cracking!

Here’s an important primer on your spine.

Before you understand what happens when you crack your back, you have to know a bit about your back itself. Down the center of your back you'll find your spine, which you can think of as "the scaffolding for the entire body," according to Cedars-Sinai Spine Center. Your spine protects your spinal cord, a bundle of nerves that transmit messages between your brain and pretty much every part of your body. With the help of vertebrae, or interlocking bones, it also supports about half the weight in your body. The average person is born with 33 vertebrae, but most adults only have 24 since some of the lower ones fuse together over time.

Your vertebrae are divided into sections: your cervical spine (your neck bones), your thoracic spine (the upper part of your back), your lumbar spine (lower back), your sacrum (which joins with your pelvis), and your coccyx (tailbone). Your vertebrae connect with each other at the back via flexible joints, and rubbery cushions known as discs are in between each one to provide some cushioning. Finally, your vertebrae connect with muscles, ligaments, and tendons throughout your back to help you do everything from pound out Russian twists at the gym to lean over and whisper in someone’s ear.

Doctors aren’t totally sure why backs crack in the first place.

“There are a number of theories on why this happens, but nobody really knows,” Neel Anand, M.D., professor of orthopedic surgery and director of spine trauma at Cedars-Sinai Spine Center in Los Angeles, tells SELF.

The most widely believed theory comes down to pockets of gas that hang out in your joints. This isn't the same kind of gas that escapes from your body after you've had a ton of beans or protein bars This gas comes from a lubricant inside your joints known as synovial fluid, which helps give nutrients to the cartilage in your joints to help them glide smoothly. Cartilage’s main job in the body is to make sure that whenever you are moving your limbs this way and that, the movement is, and feels, smooth. That’s why it’s a key player when it comes to cracking your back.

When you apply force to your joints, pressure can build up and turn into dissolved gases like oxygen, nitrogen, and carbon dioxide. The thinking is that these gases shift—and emit a cracking noise as they dissipate—when you do an extreme stretch, Dr. Anand says. The gas actually shows up on X-rays and MRIs, and your surrounding tissues quickly reabsorb it after you crack your back, Lisa A. DeStefano, D.O., chairwoman of the Department of Osteopathic Manipulative Medicine at Michigan State University, tells SELF. However, a buzzy 2015 study in PLOS One examined MRIs of knuckles cracking and argued that the cracking actually happens when a gas-filled cavity forms as the joints stretch, not when the gas bubbles themselves collapse.