“Crack!”. For some people it’s the most satisfying sound in the world. For others, it’s exactly what stops them from booking. If you’ve ever wondered what that chiropractic cracking sound is, whether it means “something has gone back into place” or whether it absolutely has to happen, here’s a clear, myth-free answer.
The essentials in 30 seconds
- The crack is gas inside the joint: when the joint surfaces separate quickly, a small cavity forms. It’s the same thing that happens when you crack your knuckles.
- The sound doesn’t mean a vertebra has “popped back in”. It isn’t a sign that anything was out of place.
- A chiropractic adjustment doesn’t have to make a sound. The crack isn’t the goal: it’s a side effect of the movement.
- If the sound makes you uneasy, just say so: we explain each adjustment before we make it and go at your pace.
What is the chiropractic crack?
The chiropractic crack is the sound that sometimes occurs when a joint separates quickly during an adjustment. Inside the joint there’s a fluid with dissolved gases; when the space suddenly increases, a small gas cavity forms and you hear a sound. It’s called cavitation, and it’s the same thing that happens when you crack your knuckles.
Think of it like opening a bottle of fizzy drink: the gas was already there, dissolved, and when the pressure changes it suddenly appears. Something similar happens in the joint, just on a tiny scale.
That’s why the crack doesn’t come from the bone, from vertebrae “clicking” together or from anything breaking. It’s a physical phenomenon inside the fluid that lubricates the joint.
Why do joints crack? What the science says
Joints crack because, when their surfaces separate suddenly, the pressure of the joint fluid drops and a gas bubble forms. Real-time MRI studies and mathematical models agree that the sound is linked to this bubble, although the exact moment it’s produced is still debated.
For decades it was thought that the noise came from a bubble bursting. In 2015, a team at the University of Alberta used real-time MRI for the first time to film several volunteers cracking their knuckles. They saw that the sound coincided with the cavity forming, and that the bubble was still there afterwards.
In 2018, two researchers published a mathematical model of the crack that reproduced the real sound from the partial collapse of the bubble. The two explanations are closer than they seem: in both, the star of the show is gas.
- 01At restThe joint fluid contains dissolved gases
- 02Quick separationThe pressure inside the joint drops
- 03Gas bubbleA small cavity forms: that’s the “crack”
Why can’t you crack the same joint twice in a row?
Because the gas needs time to dissolve back into the fluid. Classic studies on the subject describe a period of about 20 minutes during which the same joint won’t crack again. It’s like waiting for the bottle to “recharge” its fizz.
Not all joint noises are the same
The sharp “crack” of cavitation isn’t the same as the grinding or clicking you might notice in your knee when climbing stairs. Those other sounds usually come from tendons or ligaments sliding over bone. According to specialists at Penn State Health, joint noises are very common and, on their own, don’t indicate a problem.
Does the crack mean something has gone back into place?
No. The crack isn’t proof that a vertebra has gone back into place. It’s gas inside the joint, nothing more. It’s a very widespread idea, but the sound only shows that the joint surfaces have separated quickly, not that something was “out” and is now “in”.
The belief runs deep. In a study cited by an academic at the University of Technology Sydney, 49% of 100 people thought the sound meant a vertebra was being put back in place. Only 9% linked it to gas in the joint.
What’s more, the back has lots of small joints: a single movement can make several of them sound, and it’s almost impossible to tell which one each noise comes from.
The crack is a sound, not a result. What matters is how you move and feel in your daily life, not what you hear on the couch.
Does a chiropractic adjustment have to crack?
No, a chiropractic adjustment doesn’t have to make a sound. Sometimes it does and sometimes it doesn’t, and both are normal. The chiropractic crack is a side effect of the movement, not its goal. At Ôlin we never repeat an adjustment just to get the “crack”.
Some days the joint doesn’t crack because it just has, because you’re tense or simply because it isn’t going to. That’s fine. The adjustment has still been made.
Is it bad to crack your own back or knuckles?
Cracking your knuckles now and then seems harmless according to the available evidence. With your back or neck, it’s sensible not to force things: if you need to crack yourself several times a day to feel loose, it’s a sign your body is missing varied movement, not more cracks.
Harvard Health describes a famous case: an American doctor who cracked the knuckles of just one hand for decades and found no difference between his two hands on X-rays. A curious anecdote, backed up by larger studies.
What we do often see is people who live for that “crack”. They spend hours sitting, their neck feels tight or their back stiff, they twist hard in their chair… and an hour later, they’re at it again. If that sounds like you, try swapping the sharp twist for gentle, frequent movement:
1. Seated cat-cow
Sit on the edge of your chair with your feet flat and hands on your thighs. As you breathe out, round your back and bring your chin towards your chest. As you breathe in, open your chest and look slightly upwards, without forcing it.
Dose: 8 slow repetitions · twice a day
2. Gentle trunk rotation
Sitting tall, cross your arms over your chest. Slowly turn your trunk to one side until you feel a comfortable stretch, take two breaths and come back to the centre. Repeat on the other side. If it cracks, fine; if not, that’s fine too.
Dose: 6 turns each side · every 1–2 hours of sitting work
3. “Yes” and “no” with your head
With your shoulders relaxed, slowly move your head as if saying “yes”, then as if saying “no”. Small movements, without going to the end of the range and without trying to make any sound.
Dose: 5 repetitions of each · twice a day
If you wake up feeling stiff, you might like our 5-minute routine to start the day moving freely. And remember that, for the WHO, all physical activity counts: adults should aim for at least 150 minutes of moderate activity a week.
How do we approach adjustments at Ôlin?
At Ôlin we’re not chasing the crack: we want you to move more freely in your daily life. Before any adjustment we assess your mobility, strength, balance and posture, explain what we’re going to do and why, and make gentle, precise adjustments. If it cracks, fine; if it doesn’t, that’s fine too.
If the sound worries you, tell us from the start. We explain each movement before making it, go at your pace and talk it through calmly. Nobody should tense up on the couch waiting for the “crack”.
Our chiropractors have five years of full-time university training accredited by the European Council on Chiropractic Education. And if during the assessment we see something that doesn’t add up, we’ll recommend you speak to your doctor. If you’re wondering how we differ from other professions, we explain it in chiropractic, physiotherapy and osteopathy: how they differ.
Important: this article offers general information about wellbeing and healthy habits. Chiropractic at Ôlin is wellness-focused and does not replace medical care. If you notice any symptom that worries you, please see your doctor.
Frequently asked questions
Why didn’t anything crack at the chiropractor’s?
Because it doesn’t always crack, and that’s fine. The joint may have cracked recently, you may have been tense, or the adjustment may have been gentler. The sound isn’t a measure of how good the adjustment was.
What if the sound scares me?
That’s very common, especially the first time. Tell your chiropractor from the start. At Ôlin we explain each adjustment before making it, work with precise movements at your pace, and the sound, if there is one, lasts an instant and isn’t anything breaking.
What exactly is making the sound?
Gas. Inside the joint there’s a fluid with dissolved gases. When the joint surfaces separate quickly, a small gas cavity forms and the sound is produced. It isn’t bone on bone, and nothing is breaking.
How often can the same joint crack?
After cracking, a joint needs about 20 minutes before it can do so again — the time it takes for the gas to dissolve. That’s why there’s no point trying to make it crack again straight away.
Why do I feel looser after cracking my back?
Many people describe a feeling of ease after moving a joint, whether it cracks or not. But the crack isn’t the cause or the measure of that feeling: what really makes a difference day to day is moving often and in varied ways.
Want to see how your back moves, with no pressure and no compulsory “cracks”?
Your first visit costs €80 and includes a conversation about your daily life, a full assessment and a first session, with no commitment. We look forward to seeing you in Barcelona (Eixample) and at our centre in Malgrat de Mar. If it’s your first time, have a read of what happens at your first chiropractic visit.
Sources
- Kawchuk GN et al. — Real-Time Visualization of Joint Cavitation, PLOS ONE (2015)
- Chandran Suja V, Barakat AI — A Mathematical Model for the Sounds Produced by Knuckle Cracking, Scientific Reports (2018)
- Harvard Health Publishing — Knuckle cracking: annoying and harmful, or just annoying? (2018, updated 2020)
- Penn State Health — Joint cracks and pops usually not cause for concern (2017)
- University of Technology Sydney — Your back cracked, but what does the sound mean? (2026)
- World Health Organization — Physical activity, fact sheet (2024)