Short Stuff: Knuckle Cracking

Summary

Episode Overview

Podcast: Stuff You Should Know
Hosts: Josh & Chuck (with Chuck Cherry sitting in for Dave)
Episode: Short Stuff: Knuckle Cracking
Date: May 27, 2026

This “Short Stuff” episode tackles the science and myths surrounding knuckle cracking. Hosts Josh and Chuck discuss what really makes that familiar popping sound, dispel the myth that it causes arthritis, and explain both the potential downsides and small benefits of habitual knuckle cracking—all with their trademark banter, humor, and a few memorable anecdotes.

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Key Discussion Points and Insights

1. What Actually Happens When You Crack Your Knuckles

• [01:34] Josh cracks his knuckles live:
  Josh: "I am. Did you hear that?"
• [01:48] Chuck explains the mechanics:
  • Joints are where two bones meet but don’t touch, surrounded by a capsule filled with synovial fluid.
  • Cracking stretches this capsule, lowering the pressure inside, which causes dissolved gases to form bubbles.
  • When these bubbles collapse, it causes the characteristic “pop.”
  • Chuck: "Your bones don’t actually come together... That’s not what cracking your knuckles is, it turns out. Instead, it has everything to do with the space... the synovial fluid." [02:20]
• [03:44] Josh summarizes:
  • "If you stretch that joint far enough, like, you know, trying to crack your knuckles, the pressure in the capsule goes so low that it just pops those bubbles. And that’s the popping sound that we're hearing."
• [02:07] Myths addressed: It's not bones grinding together, nor does it automatically cause harm as kids are often warned.

2. The Cycle of Knuckle Cracking & Cavitation

• [01:48, 04:08]
  • You can’t immediately re-crack the same knuckle; it takes 20-30 minutes for gases to dissolve back into the synovial fluid.
  • Chuck: "I can’t do it again because I have to wait 20 to 30 minutes for the air bubbles to come back and cavitate once more."

3. The Arthritis Myth—The Dr. Donald Unger Experiment

• [06:33] The hosts discuss Dr. Donald Unger’s lifelong experiment:
  • He cracked only one hand’s knuckles daily for 60 years, never the other.
  • X-rays showed no difference in arthritis between hands.
  • Chuck: "After 60 years, he finally said, okay, it's time. And he x rayed his hands." [07:16]
  • Josh: "He x rayed himself on the reg and eventually decades later, came to the conclusion that he doesn't have any arthritic difference in his hands. Case closed." [07:41]

4. Other Effects of Habitual Knuckle Cracking

• [08:00] While arthritis is not a concern, other issues may arise:
  • Soft tissue damage to ligaments and the capsule
  • Decreased grip strength
  • Chuck: "...there was other damage, like soft tissue damage... and that they had a decrease in grip strength. So if you crack your knuckles a lot, like, don’t even think about holding a glass of water with just one hand." [08:44]
• Habitual cracking can cause ligament laxity (looseness), swelling, and in extreme cases, sprains or minor injuries.
• Analogies to baseball pitchers, who experience similar issues from repeated motion.
  • Chuck: "It also happens in pitchers, too... over the years, just throwing over and over... they're stretching those ligaments suddenly, violently, basically, which is kind of what you're doing when you crack your knuckles." [09:26]
  • Josh: "...these days there's been more and more instances of Tommy John surgery being required..." [10:15]

5. Notable Studies & Habitual Character Traits

• [10:47]
  • 1990 study: Regular crackers had reduced grip strength, more swelling.
  • Study: Knuckle cracking correlated with other habits (manual labor, nail-biting, smoking, drinking).
  • Josh: "...if you’re a habitual knuckle cracker, you are more likely to be a manual laborer. More likely to bite your nails, as I do. Smoke cigarettes, which I don't, and drink alcohol, which I do."

6. Are There Any Benefits?

• [11:31] There is a small benefit—relaxation via Golgi tendon organs:
  • Cracking relieves some muscle tension around joints—"yoga for your knuckles."
  • Chuck: "So you can feel like your hands feel pretty mellow after cracking your knuckles. I saw it described as yoga for your knuckles." [12:08]
  • Also compared to back cracking.

7. Aging & Cracking Sounds in Joints

• [12:16] Discussion of normal noises from joints as people age (knees, ankles):
  • Generally, nothing to be alarmed about unless accompanied by pain.
  • Josh: "When I walk downstairs, my right ankle, like, on every step just goes pop, pop, pop. So those things happen. I don't think anyone knows exactly where that comes from... maybe a tendon sliding over a bumpy surface..." [12:37]
  • Chuck: "It is alarming, though, for sure." [13:06]

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Notable Quotes & Memorable Moments

• [02:20] Chuck: "If your bones ground together, you would not be able to think of anything else but your bones grinding together because you would be in so much pain..."
• [03:44] Josh: "That’s right. So they... form those bubbles. And if you stretch that joint far enough, the pressure in the capsule goes so low that it just pops those bubbles. And that's the popping sound that we're hearing."
• [07:41] Josh: "He x rayed himself on the reg and eventually decades later, came to the conclusion that he doesn't have any arthritic difference in his hands. Case closed."
• [08:51] Josh: "As you age, grip strength is important. So it's definitely not a harmless thing."
• [12:08] Chuck: "So you can feel like your hands feel pretty mellow after cracking your knuckles. I saw it described as yoga for your knuckles."
• [12:32] Josh: "Oh. Oh, yeah. Like, oh, God, here we go. Or something like that." (On making involuntary sounds when standing up with age.)

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Timestamps for Important Segments

• [01:34] – Live knuckle cracking demonstration
• [02:20] – What the popping sound really is
• [03:44] – How pressure in the joint creates the “pop”
• [04:08] – Cavitation and why you can’t immediately re-crack
• [06:33] – Dr. Donald Unger’s arthritis experiment begins
• [07:41] – Confirmation: No link to arthritis found
• [08:44] – Habitual cracking: grip strength and soft tissue damage
• [09:26] – Comparison to repetitive sports injuries (pitchers)
• [10:47] – Studies: other risk factors and traits of crackers
• [11:31] – Relaxation effects (Golgi tendon organs)
• [12:16] – Joint noises and aging

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Final Takeaways

• The common myth—cracking knuckles causes arthritis—is not supported by science.
• The popping noise comes from collapsing bubbles in joint fluid, not bones grinding.
• Habitual cracking may decrease grip strength and cause minor soft tissue problems.
• Some minor relaxation benefit may occur thanks to reduced muscle tension.
• Random pops and cracks in other joints are normal, especially as people age, unless accompanied by pain.
• The episode blends clear science with the hosts' signature humor, making it both informative and entertaining.

Transcript

[Podcast Announcer]

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[Josh]

Guaranteed Human.

[Chuck]

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[Josh]

I am. Did you hear that?

[Chuck]

Yeah. That wasn't like a foldy effect.

[Josh]

No, I was cracking my knuckles. I'm a knuckle cracker. I don't do it. I did it a lot when I was a kid, but I still do it some.

[Chuck]

This is what my knuckles sound like when I crack them. That's it. Yeah. I can't do it again because I have to wait 20 to 30 minutes for the air bubbles to come back and cavitate once more.

[Josh]

Yeah, well, tell everybody what's going on here. I know there was a lot of when you were young, everyone was like, it'll give you arthritis and it's your bones grinding together. And that's what cracking your knuckles is. And that can't be good for you.

[Chuck]

Yes. If your bones ground together, you would not be able to think of anything else but your bones grinding together because you would be in so much pain that you would know your bones are Grinding together. That's not what cracking your knuckles is, it turns out. Instead, it has everything to do with the space in the area around where your bones come together. Your bones don't actually come together.

[Josh]

That's right. Where there's a joint, that is where two bones meet, but they're separate, and they're held together by ligaments and connective tissues and all that stuff. But there's also a very other key ingredient in there. It's called synovial fluid. It's a thick, clear liquid that kind of encases that area, right?

[Chuck]

Yeah, it's thick. It tastes just like Orange Crush, surprisingly. And when you pop your knuckle, what you're doing is stretching or bending the ligaments and connective tissues and the synovial fluid there, too. Right. So when you do that, that capsule is what it's called, the connective tissue capsule that includes the synovial fluid. It gets stretched, which increases its volume. And then suddenly the pressure inside the capsule in that synovial fluid, it goes down, it decreases in pressure, which means that all these gases that used to just be part of the solution now are part of the problem. I mean, now turn into bubbles.

[Josh]

That's right. So they become, you know, they form those bubbles. And if you stretch that joint far enough, like, you know, trying to crack your knuckles, the pressure in the capsule goes so low that it just pops those bubbles. And that's the popping sound that we're hearing.

[Chuck]

There you go. Not your bones rubbing together. Okay, I want you to go to recess and tell your friends that is not your bones rubbing together.

[Josh]

Yeah. And then the cavitation you mentioned earlier, I think before we break, we should just clear that up. You said 20 to 30 minutes. That is how long it takes for that gas to re. Dissolve into that joint fluid and cavitation is possible again.

[Chuck]

Yeah. Go watch that. That's when the bubble starts cavitating my knuckles.

[Josh]

Yeah, exactly.

[Chuck]

Oh, I just did one again. Okay, I say we take a little break and come back and talk about how we know that cracking your knuckles doesn't give you arthritis.

[Josh]

All right, we'll be right back.

[Chuck]

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[Josh]

Yeah, it was a long time ago. And, you know, I'm Gen X, so I grew up talking on the phone with my friends in high school and stuff, and it was a really fond memory.

[Chuck]

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[Josh]

That's right. Over that 150 years, there's been a lot of connection with people, whether it was me in high school or family, connecting with one another long distance or those long distance relationships. And AT&T has been there for it all. Connecting changes everything. AT&T. Hey everyone. Your outdoor space should feel like you. And Wayfair has the pieces that actually match the vibe of what you're going for.

[Chuck]

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[Josh]

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[Chuck]

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[Josh]

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[Chuck]

Every home. Chuck, I know we've talked about this guy before, Dr. Donald Unger. I think we did a video about him.

[Josh]

Yeah.

[Chuck]

But he. You know what? I'll bet we talked about him in the IG Nobel prize episode because he wanted ignoble for this. But essentially he conducted an experiment for 60 years because he wanted to prove his mother wrong. And the only cracked that the knuckles. And I think his left hand never cracked them on his right hand.

[Josh]

That's crazy.

[Chuck]

And then after 60 years, he finally said, okay, it's time. And he x rayed his hands.

[Josh]

Yeah. If he didn't have the compulsion to crack his knuckles, I could see how this happened. But if you are a knuckle cracker, you're kind of. You feel compelled to do it. So I can't imagine what it would have taken to not crack the knuckles on one hand for that many years. It must have been really tough.

[Chuck]

Yeah, sure.

[Josh]

That's my guess. So yeah, he did this over his lifetime. He x rayed himself on the reg and eventually decades later, came to the conclusion that he doesn't have any arthritic difference in his hands. Case closed.

[Chuck]

He had nad no Arthritic difference.

[Josh]

That's right.

[Chuck]

That's not to say, though, that even if you don't get arthritis from cracking your knuckles, another thing you can tell your friends at recess, do they even have recess anymore? I guess maybe hour long screen time?

[Josh]

No, they have recess.

[Chuck]

Okay, great. There is damage that you can do from cracking your knuckles habitually. There was a guy named Raymond Broder, and he examined 300 people who cracked their knuckles to look at what their joints looked like. And compared to the control group, no difference with arthritis. Again. But there was other damage, like soft tissue damage to that the ligaments and the synovial fluid capsule and that they had a decrease in grip strength. So if you crack your knuckles a lot, like, don't even think about holding a glass of water with just one hand.

[Josh]

Yeah. Which, you know, as you age, grip strength is important. So it's definitely not a harmless thing. There's some other possible side effects, something called ligament laxity, which is basically looseness. So over time, if you're just doing this a lot, that's what leads to the reduced grip strength and sometimes sort of overall hand function.

[Chuck]

Yep.

[Josh]

I think in rare cases, if you have a really weird method or forceful method, or you're a little too aggressive with it, you can get some soft tissue swelling around the knuckles in the joint.

[Chuck]

Yeah. You can just straight up injure yourself if you. You can, like dislocate a joint, you can injure your tendons. And even if you don't straight up injure yourself, just habitually cracking your knuckles over time, the stretching of the ligaments can it. Like you said, the grip strength thing is a big deal, just even without cracking your knuckle. So it also happens in pitchers, too. Major league pitchers. Imagine minor league pitchers, too, but over the years, just throwing over and over and over again, they're stretching those ligaments suddenly, violently, basically, which is kind of what you're doing when you crack your knuckles. They're just doing it with different ligaments. But that is why Oral Hershiser's right arm just dangles uselessly at his side because it's been ruined. He ruined it pitching.

[Josh]

Yeah, I mean, I know you're kind of kidding, but sad but true, like, especially these days, there's been more and more instances of Tommy John surgery being required because pitchers are throwing harder and harder. And if you're not, you know, able to get it near 100 miles an hour these days, you're not gonna have much of a chance. So it's a real problem in baseball

[Chuck]

that was a real bring down from my joke.

[Josh]

Yeah. I just love that you love saying Earl Hershiser.

[Chuck]

Sure. Who else can I say?

[Josh]

Boy, he was great. There was a study in 1990 that confirmed the grip strength thing. I think they studied 74 people who regularly crack their knuckles, and their average grip strength was definitely lower. And they had more instances of hand swelling than the 226 people who did not crack. And another interesting thing is they found that in another study that if you're a habitual knuckle. Knuckle cracker, you are more likely to be a manual laborer. More likely to bite your nails, as I do. Smoke cigarettes, which I don't, and drink alcohol, which I do.

[Chuck]

Yeah, so you're, you know, three for five.

[Josh]

Yeah, I don't. Manual labor, so I shouldn't count that one.

[Chuck]

So there is some benefits to actually cracking your knuckles, though, too. We're not just hating on cracking your knuckles. There's something called the Golgi tendon organs. Not the Golgi apparatus. That's a different episode altogether. The Golgi tendon organs sense muscle tension, and when you crack your knuckles, you're actually relieving some muscle tension. So the muscles around the joints, when you crack them, get relaxed. So you can feel like your hands feel pretty mellow after cracking your knuckles. I saw it described as yoga for your knuckles.

[Josh]

Oh, interesting.

[Chuck]

Yeah, I thought so, too.

[Josh]

So, like, getting your back cracked or something?

[Chuck]

Basically, yeah. But for your knuckles.

[Josh]

Yeah. We found one more thing, you know, like, I'm at the age where, you know, if I kneel down to get something, you're gonna hear a couple. A snap, crackle and a pop, maybe coming from some part of my body.

[Chuck]

Do you make an involuntary sound too, when you're getting up? I do.

[Josh]

Oh. Oh, yeah. Like, oh, God, here we go. Or something like that.

[Chuck]

Like, you can't not do it.

[Josh]

Yeah, for sure. And when I walk downstairs, my right ankle, like, on every step just goes pop, pop, pop. So those things happen. I don't think anyone knows exactly where that comes from. There's speculation. It could be just like, you know, if it's your knee, it may be your kneecap rubbing on the bones or something like that, or maybe a tendon sliding over a bumpy surface or something like that. So I don't think it's anything to be alarmed about.

[Chuck]

It is alarming, though, for sure.

[Josh]

Yeah. Because it comes with age. So every new pain and sound is like, huh, that didn't happen a few years ago.

[Chuck]

Exactly. I should go sit down for a while.

[Josh]

Right?

[Chuck]

You got anything else for short Stuff Guy?

[Josh]

I got nothing else. I can't crack my knuckles, so. Oh, wait, there went one. Recavitated.

[Chuck]

So what does that mean?

[Josh]

I think that means short stuff is out.

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