WEBVTT - Why Do Our Knuckles Crack? 0:00:01.160 --> 0:00:04.720 Hey, welcome to side Stuff, a production nuff iHeartRadio. I'm 0:00:04.720 --> 0:00:08.119 Hoory Champ, and today we are taking a crack at 0:00:08.360 --> 0:00:13.720 knuckle cracking. Why do we do it, why does it happen? 0:00:14.040 --> 0:00:17.040 And is it bad for you? We're going to talk 0:00:17.079 --> 0:00:20.440 to a couple of experts about it, including one researcher 0:00:20.480 --> 0:00:24.280 who thinks they figured out the real reason why joins 0:00:24.480 --> 0:00:28.160 made that popping sound. It's not what you think, So 0:00:28.200 --> 0:00:31.200 stop wringing your hands, get cracking with us as we 0:00:31.320 --> 0:00:34.080 snap up and answer to the question why do our 0:00:34.200 --> 0:00:35.600 knuckles crack? 0:00:39.640 --> 0:00:39.800 Hey? 0:00:39.880 --> 0:00:42.600 Everyone, So, one of the fun things about being a 0:00:42.720 --> 0:00:46.360 current is seeing something about yourself end up in your kids. 0:00:47.040 --> 0:00:50.200 It could be your looks, or your personality or even 0:00:50.240 --> 0:00:54.760 your mannerisms. It's usually fun, but sometimes can be a 0:00:54.800 --> 0:01:12.120 little unsettling. Cannot a minute, WHOA, I'm talking me correctly. Yes, 0:01:12.440 --> 0:01:15.199 I am a knuckle cracker, and so is my daughter, 0:01:15.680 --> 0:01:19.440 but my spouse and my son not so much, which 0:01:19.480 --> 0:01:22.600 made me wonder why do some people's knuckles crack and 0:01:23.000 --> 0:01:27.160 some don't? What actually makes that sound? And is it 0:01:27.360 --> 0:01:29.880 bad for you? And if it is bad, why do 0:01:29.959 --> 0:01:33.120 we keep doing it? As it turns out, knuckle cracking 0:01:33.319 --> 0:01:35.760 has to do with the type of joint we have 0:01:36.080 --> 0:01:38.839 in our bodies. To tell us about this type of joint, 0:01:39.120 --> 0:01:43.040 I reached out to doctor Neilima Sharma, a biologist and 0:01:43.160 --> 0:01:48.880 researcher at University College London. Well, thank you so much, 0:01:48.920 --> 0:01:50.200 Taka Sharma for joining us. 0:01:50.640 --> 0:01:51.640 Sure, that's my pleasure. 0:01:51.840 --> 0:01:56.080 Today we're talking about knuckle cracking and here it has 0:01:56.120 --> 0:01:59.160 something to do with something called a sinovial joint. Is 0:01:59.200 --> 0:02:01.240 that how you pronounce this iino you' or sinovio? 0:02:01.400 --> 0:02:03.440 I guess it may depend on whether you're on the 0:02:03.560 --> 0:02:04.440 side of the Atlantic. 0:02:06.760 --> 0:02:07.680 How do you pronounce it? 0:02:08.440 --> 0:02:10.080 I call it a synovial joint? 0:02:10.400 --> 0:02:12.320 Syno jo. We'll go with them. Can you tell us 0:02:12.320 --> 0:02:13.760 what is the sinovial joint? 0:02:13.880 --> 0:02:16.480 So, sinobal joints are the kind of joints that are 0:02:16.560 --> 0:02:20.760 found in your elbow or your hip. They are characterized 0:02:20.919 --> 0:02:26.320 by relative sliding of two surfaces next to each other. So, 0:02:26.440 --> 0:02:31.040 if you want a common example, a door hinge functions 0:02:31.200 --> 0:02:34.239 very similar to how a cynobial join functions. You have 0:02:34.360 --> 0:02:37.320 two metal surfaces in a door hinge that are sliding 0:02:37.480 --> 0:02:38.560 with respect to each other. 0:02:39.919 --> 0:02:41.880 So most of the joints in your body are what 0:02:42.000 --> 0:02:46.120 are called sinobial joints or synovial joints as other people 0:02:46.200 --> 0:02:48.320 pronounce it, And those are the kinds of joints that 0:02:48.440 --> 0:02:51.720 are like door hinges or like ball of socket joints, 0:02:51.919 --> 0:02:55.000 where the surface of one bone curves around the surface 0:02:55.080 --> 0:02:57.880 of the other bone, and they rotate and slide around 0:02:57.919 --> 0:03:00.800 each other. That's one way to join two boats together. 0:03:01.320 --> 0:03:03.600 Another kind of joint that you see in nature and 0:03:03.720 --> 0:03:07.080 in some parts of our body are cartilaginous joints. 0:03:08.560 --> 0:03:10.840 So these are the joints found in your spine. So 0:03:10.960 --> 0:03:13.880 here you have two bony elements which are very stiff, 0:03:14.240 --> 0:03:17.880 and they are connected by a soft cartilage element in 0:03:17.960 --> 0:03:20.400 the middle. Okay, so you can imagine, like the way 0:03:20.480 --> 0:03:22.280 they function is by bending. 0:03:23.639 --> 0:03:27.040 So this kind of join cartilaginous joint don't have any 0:03:27.280 --> 0:03:30.680 moving parts. It's basically like joining the ends of two 0:03:30.760 --> 0:03:33.880 sticks of wood together with a short rubber tube. The 0:03:34.000 --> 0:03:37.160 joint bends by bending the tube. Now, when we were 0:03:37.280 --> 0:03:41.800 evolving as primitive animals, we first evolved bones and cartilage, 0:03:42.080 --> 0:03:45.720 and initially all of our joints were cartilaginous. You can 0:03:45.760 --> 0:03:48.880 imagine we were blobby fish swimming in the ocean and 0:03:49.200 --> 0:03:51.640 we had a skeleton, but it was all put together 0:03:51.760 --> 0:03:55.320 with basically rubber joints. But then at some point we 0:03:55.400 --> 0:03:59.960 started developing this new kind of joint, synovial joint, which 0:04:00.240 --> 0:04:03.800 had two moving, rotating parts. Now, if you have two 0:04:03.920 --> 0:04:07.280 bones rotating and rubbing against each other, after a while, 0:04:07.520 --> 0:04:11.120 they'll wear each other out and get creaky. So a 0:04:11.200 --> 0:04:13.560 feature of these sinovial joints is that they have a 0:04:13.720 --> 0:04:16.560 gap in between the two bones which is filled with 0:04:17.080 --> 0:04:17.760 a lubricant. 0:04:19.279 --> 0:04:22.360 And again, like an adore hinge, you need to keep 0:04:22.520 --> 0:04:26.120 the joint lubricated, so you oil these hinges very often 0:04:26.640 --> 0:04:30.200 to maintain a seamless function. In the same way, our 0:04:30.279 --> 0:04:33.320 sinoval joints are also highly lubricated. 0:04:33.640 --> 0:04:36.120 I see, I'm not very handy around the house, so 0:04:36.160 --> 0:04:39.200 I don't really lubricate my hinges, maybe as much as 0:04:39.240 --> 0:04:44.040 I should. But what's special about a sainovial joint as 0:04:44.080 --> 0:04:45.880 opposed to any other kinds of joints. 0:04:46.279 --> 0:04:51.240 So this substance called sinovial fluet, which exists between these 0:04:51.320 --> 0:04:55.920 two surfaces that gives our sinoval joints that's lubricating properties. 0:04:57.120 --> 0:05:00.720 So snovial joints have a gap between the two surfaces 0:05:00.800 --> 0:05:03.320 of the bones that slide past each other, and this 0:05:03.560 --> 0:05:06.919 gap is filled with a special liquid that is basically 0:05:07.200 --> 0:05:09.479 like a super lubricate. 0:05:10.600 --> 0:05:13.719 So this is a very cool fact about sinoval sewage. 0:05:13.880 --> 0:05:18.120 Particularly the sinoval fluid, is a substance that is known 0:05:18.200 --> 0:05:21.760 to have one of the lowest coefficient of friction in 0:05:22.200 --> 0:05:26.080 both biological materials as well as engineered materials. 0:05:26.400 --> 0:05:28.040 Really, it's super slippery. 0:05:28.360 --> 0:05:32.280 Yeah, it's super slippery. It's more slippery than what ice 0:05:32.360 --> 0:05:35.040 on ice feels like. Really, and ice on ice is 0:05:35.080 --> 0:05:40.560 super slippery. Yeah, whoah, more slippery than oil. Yeah, absolutely, 0:05:40.839 --> 0:05:43.680 And that's why you have to lubricate your door headges 0:05:44.240 --> 0:05:45.960 get a few months now. 0:05:46.000 --> 0:05:48.359 You're making me feel guilty, But. 0:05:48.440 --> 0:05:50.680 You do not have to lubricate your joints as much. 0:05:50.880 --> 0:05:53.280 They function for sixty years of age if you take 0:05:53.320 --> 0:05:54.239 care of them properly. 0:05:55.560 --> 0:05:59.680 Now, these special sinovial joints with the two bones separated 0:05:59.720 --> 0:06:03.359 by gap filled with a super slippery liquid are basically 0:06:03.480 --> 0:06:06.760 the reason our knuckles crack. We'll get into the physics 0:06:06.839 --> 0:06:09.400 of why that happens later in the program. But what 0:06:09.520 --> 0:06:12.640 this type of joint also did is give our vertebrate 0:06:12.800 --> 0:06:16.159 ancestors essentially a superpower. 0:06:17.880 --> 0:06:20.320 This kind of joint. So you can imagine that when 0:06:20.320 --> 0:06:23.000 I'm moving my elbow, I do not really face a 0:06:23.120 --> 0:06:26.160 resistance while I'm moving it. So it's I know, will 0:06:26.240 --> 0:06:29.520 joints allow you to be more mobile and faster. I 0:06:29.560 --> 0:06:32.200 can move my elbow so much faster because there's absolutely 0:06:32.279 --> 0:06:33.880 no resistance here and all I have to do is 0:06:33.960 --> 0:06:37.400 turn my muscle on. This would have allowed animals to 0:06:37.839 --> 0:06:40.080 operate quickly. So if I'm a predator and I have 0:06:40.200 --> 0:06:43.600 a joint that moves early fast, I am definitely able 0:06:43.640 --> 0:06:48.039 to cash more prey and I'm also able to evade predators. 0:06:49.160 --> 0:06:52.440 So they must definitely have given animals and edge over 0:06:52.600 --> 0:06:55.440 other animals who did not have these joints. And maybe 0:06:55.480 --> 0:06:57.960 that's why they spread so fast that most vertebrates that 0:06:58.040 --> 0:07:00.719 we'd know now do have a lot of signe joints. 0:07:00.839 --> 0:07:03.880 Oh, that could have been their secret weapon to take 0:07:03.960 --> 0:07:04.599 over the world. 0:07:05.720 --> 0:07:11.480 Yeah, absolutely, WHOA, this is your speculation, but definitely interesting speculation. 0:07:12.320 --> 0:07:17.200 Yes, so sygnobil joints could possibly be the reason you, me, 0:07:17.400 --> 0:07:22.120 and most vertebrate animals are here. Cinovial joints are easier 0:07:22.200 --> 0:07:25.400 to move and therefore faster, and they have a wider 0:07:25.520 --> 0:07:29.080 range of motion than the cartilaginous type of joint, which 0:07:29.200 --> 0:07:32.640 could have given the vertebrates that had sinobial joints the advantage. 0:07:33.200 --> 0:07:37.160 Now it's interesting to think about what exactly prompted vertebrates 0:07:37.240 --> 0:07:39.920 to develop this type of joint. According to doctor Sharma, 0:07:40.240 --> 0:07:42.960 the conventional wisdom for at least the last hundred years 0:07:43.040 --> 0:07:45.880 or so has been that vertebrates evolved this kind of 0:07:46.040 --> 0:07:49.800 joint when they moved from the ocean to land. The 0:07:49.920 --> 0:07:53.680 idea is that sinovial joints are better for standing and walking. 0:07:54.920 --> 0:07:58.480 People used to think that cinobil joints only evolved because 0:07:58.640 --> 0:08:02.520 animals moved out from water to land, and because on 0:08:02.720 --> 0:08:05.520 land you have to bear larger loads. You need like 0:08:05.640 --> 0:08:08.640 these joints which do not become unstable. 0:08:08.360 --> 0:08:11.880 Because cartilaginist joints are unstable. 0:08:11.640 --> 0:08:13.800 Because they are like a rubber tube. Now, if I 0:08:13.920 --> 0:08:16.360 stand on a rubber tube, it can compress or it 0:08:16.440 --> 0:08:18.280 can buckle out of shape. 0:08:18.400 --> 0:08:19.000 I see. 0:08:19.480 --> 0:08:22.560 It's not that sinovil joints don't become unstable, but they 0:08:22.600 --> 0:08:26.400 are definitely more stable than cartilaginous joints. If you would 0:08:26.520 --> 0:08:29.440 want similar range of motion out of the two joints, 0:08:30.640 --> 0:08:33.760 so there was a conventional wisdom for many years we 0:08:33.880 --> 0:08:37.440 have cygnovial joints because we needed them to walk on land. 0:08:38.040 --> 0:08:40.599 But the reason I reached out to doctor Sharma is 0:08:40.640 --> 0:08:43.240 that she's the lead author in a recent study that 0:08:43.480 --> 0:08:45.959 says this is not true. 0:08:46.640 --> 0:08:47.679 So this is a paper. 0:08:47.960 --> 0:08:50.480 In fact, I was published last year, and I was 0:08:50.840 --> 0:08:54.679 researching the question of when the joints evolved, whether or 0:08:54.679 --> 0:08:56.720 not skates and sharks at sinobile joints. 0:08:57.640 --> 0:09:00.400 What doctor Sharma and her colleagues did, by study current 0:09:00.440 --> 0:09:03.640 animals and studying the fossils of ancient animals, was to 0:09:03.760 --> 0:09:07.920 sort of pinpoint the evolution of sinovial joints and therefore 0:09:08.240 --> 0:09:12.319 when exactly animals started to be able to possibly start 0:09:12.559 --> 0:09:15.800 cracking their knuckles. And they dated it to about four 0:09:16.080 --> 0:09:20.760 hundred million years ago. Now this date is significant according 0:09:20.760 --> 0:09:23.920 to doctor Sharma for two reasons. And they're going with 0:09:24.040 --> 0:09:26.360 me here for a second. I promise it'll be worth it. 0:09:26.920 --> 0:09:30.880 That date four hundred million years ago is before animals 0:09:31.000 --> 0:09:34.280 moved from the ocean to land. So the reason we 0:09:34.360 --> 0:09:37.920 have synovial joints is not so we could stand up. 0:09:38.559 --> 0:09:43.120 But wait, if that's not the reason, then what is well, 0:09:43.360 --> 0:09:46.559 four hundred million years ago. It's also the time when 0:09:46.840 --> 0:09:51.920 jaws were first developed. That's right, before four hundred million 0:09:52.000 --> 0:09:55.120 years ago, fishes just kind of had a circular mouth, 0:09:55.440 --> 0:09:58.920 sort of like lampreeze or leeches. But then four hundred 0:09:59.000 --> 0:10:03.600 million years ago, vertebrates evolved jaws that could open and close, 0:10:03.920 --> 0:10:06.959 and that could bite and chomp and prey. And this 0:10:07.120 --> 0:10:10.319 brings up the crazy idea that maybe the reason we 0:10:10.440 --> 0:10:13.800 evolved synovial joints, and therefore the reason we can crack 0:10:13.840 --> 0:10:17.920 our knuckles, could have been to eat better. Okay, to 0:10:18.040 --> 0:10:20.920 be fair, the evolution of sinnovial joints and the evolution 0:10:21.080 --> 0:10:24.000 of jaws happening at the same time could just be 0:10:24.160 --> 0:10:27.480 a coincidence, and there are sort of examples of old 0:10:27.559 --> 0:10:30.559 fish that maybe have sinobial joints in their fins and 0:10:30.840 --> 0:10:34.080 not their jaws. But still it does point to one 0:10:34.240 --> 0:10:37.920 possible answer to the question why do we crack our knuckles. 0:10:39.440 --> 0:10:43.439 Here's my hypothesis that knuckle cracking is a byproduct of 0:10:43.600 --> 0:10:46.000 developing these kinds of joints so that we could move 0:10:46.120 --> 0:10:49.480 faster and be better at eating and moving and running 0:10:49.520 --> 0:10:52.360 and swimming, and eventually walking and running it's like it's 0:10:52.400 --> 0:10:54.719 something we can't avoid if we wanted to have this 0:10:54.880 --> 0:10:55.400 kind of joint. 0:10:55.800 --> 0:10:59.199 Yeah, I guess not. It is definitely a byproduct of 0:10:59.360 --> 0:11:02.320 the evolution of these kind of joints and an interesting 0:11:02.440 --> 0:11:03.000 vibe product. 0:11:04.080 --> 0:11:07.240 In other words, if we couldn't crack our knuckles, we 0:11:07.480 --> 0:11:11.080 probably wouldn't be here. Okay, I just had one more 0:11:11.200 --> 0:11:15.480 question or doctor Sharma. Okay, last question, do Korsharma? Can 0:11:15.559 --> 0:11:16.400 you crack your knuckles? 0:11:16.800 --> 0:11:17.000 Yes? 0:11:17.760 --> 0:11:21.520 Oh my goodness. Oh well, it's really loud. 0:11:24.120 --> 0:11:25.719 To be honest, I don't think I've done this in 0:11:25.720 --> 0:11:29.400 the last five years. Oh really, Yeah, I do have 0:11:30.280 --> 0:11:31.199 because usually. 0:11:31.080 --> 0:11:33.599 Oh, you have this ability to crack your knuckles, but 0:11:34.000 --> 0:11:37.480 it's not a composion for you. No. That brings us 0:11:37.559 --> 0:11:39.920 the next question we're going to answer in this episode, 0:11:40.160 --> 0:11:43.319 which is, if we can crack our knuckles, why do 0:11:43.400 --> 0:11:45.360 we do it? And why do some of us do 0:11:45.480 --> 0:11:49.040 it compulsively? When we come back, I'm gonna talk Jane 0:11:49.080 --> 0:11:53.200 neuroscientists about this, and we're gonna address whether cracking your 0:11:53.280 --> 0:11:56.720 knuckles is that for you. So stay with us. We'll 0:11:56.760 --> 0:12:11.160 be right cracked, but I mean we'll be right back. Hey, 0:12:11.240 --> 0:12:14.959 we'll come back we're talking about cracking our knuckles, and 0:12:15.320 --> 0:12:17.760 so far we've learned the reason we can crack our 0:12:17.840 --> 0:12:20.720 knuckles is that it's a feature that came with an 0:12:20.880 --> 0:12:25.200 upgrade in the joints of our early vertebrate ancestors. Those 0:12:25.240 --> 0:12:27.000 are the joints in your body are what are called 0:12:27.120 --> 0:12:32.760 sinovial or synovial joints, and they're pretty good. Here. Try this, 0:12:33.320 --> 0:12:36.199 if you can swing your arms around in a circle 0:12:36.840 --> 0:12:40.200 and open and close the fingers in your hand. Isn't 0:12:40.240 --> 0:12:43.160 it incredible how easy and smooth it is to do that, 0:12:43.960 --> 0:12:46.520 and be amazed at what a wide range of motion 0:12:46.840 --> 0:12:50.079 each of your joints has. Well, it's all due to 0:12:50.400 --> 0:12:56.319 signovial joints, but sometimes they do crack. We'll get to 0:12:56.360 --> 0:12:59.240 the physics and the fluid dynamics of why that happens. 0:12:59.480 --> 0:13:01.520 But first I thought we could answer the question of 0:13:01.760 --> 0:13:05.480 why we crack our knuckles from a psychological point of view, 0:13:06.120 --> 0:13:08.559 Why are we compelled to crack our knuckles and why 0:13:08.640 --> 0:13:11.960 does it annoy certain people? To dig into the mind 0:13:12.040 --> 0:13:15.240 of the knuckle cracker, I reached out to doctor Dwayne Godwin, 0:13:15.480 --> 0:13:18.920 a psychologist and neuroscientist at Wake Forest University and the 0:13:19.040 --> 0:13:23.719 co author with me of the book Out of Your Mind. Well, 0:13:23.800 --> 0:13:25.480 thanks doctor Godwin for joining us again. 0:13:25.720 --> 0:13:27.000 Hey or hey, how are you doing. 0:13:27.480 --> 0:13:29.360 I'm great. I'm cracking my knuckles here. 0:13:29.720 --> 0:13:30.280 Oh are you? 0:13:31.480 --> 0:13:33.599 I can't stop. I can't stop. That's the that's the 0:13:33.720 --> 0:13:36.280 question we're trying to answer today. Can you character knuckles? 0:13:36.320 --> 0:13:37.480 You just don't do it. I can. 0:13:38.080 --> 0:13:39.160 It's not very impressive. 0:13:40.200 --> 0:13:41.880 Oh oh boy, that was pretty loud. 0:13:42.120 --> 0:13:42.320 Yeah. 0:13:42.600 --> 0:13:43.719 Oh it's a microphone. 0:13:46.200 --> 0:13:48.560 The first thing I asked doctor Cockwin was what does 0:13:48.600 --> 0:13:53.040 psychologists think of knuckle cracking? And apparently the answer is 0:13:54.160 --> 0:13:54.720 they don't. 0:13:56.600 --> 0:13:56.800 Yeah. 0:13:56.880 --> 0:14:00.920 You know, there's not an extensive literature on knuckle cracking. 0:14:01.720 --> 0:14:04.120 With a lot of the other things we talk about, 0:14:04.400 --> 0:14:07.360 there's usually something like a study, there's scales that you 0:14:07.440 --> 0:14:12.199 can compare with advanced neuroimagery. But knuckle cracking, you know, 0:14:12.440 --> 0:14:14.640 it doesn't really hurt you for the most part. It 0:14:14.760 --> 0:14:18.559 doesn't produce the kind of euphoria that you might associate 0:14:18.600 --> 0:14:21.400 with a drug, so it's harder to study in that way. 0:14:21.880 --> 0:14:23.960 I see, it's not high in the priority list of 0:14:24.120 --> 0:14:26.680 the nih or National Science Foundation. 0:14:26.880 --> 0:14:29.360 You know, if you're sort of balancing things out, Oh am, 0:14:29.440 --> 0:14:32.960 I going to look at brain tumors versus knuckle cracking. 0:14:33.160 --> 0:14:35.360 Yeah, but not everyone can study brain tomors. I mean, 0:14:35.640 --> 0:14:40.960 somebody's got to study the knuckles. Yeah, So knuckle cracking 0:14:41.320 --> 0:14:44.640 is not a high priority in the scientific community, although 0:14:44.840 --> 0:14:47.800 we did find a couple of case reports where psychologists 0:14:47.920 --> 0:14:50.160 have treated people who said they had a problem with 0:14:50.480 --> 0:14:51.600 cracking their knuckles. 0:14:53.840 --> 0:14:57.080 Yeah, there are a few case reports where this joint 0:14:57.280 --> 0:15:02.000 cracking or clicking becomes excessive or distressing or really hard 0:15:02.040 --> 0:15:05.960 to stop. One of the reports described compulsive joint clicking 0:15:06.160 --> 0:15:10.640 driven by an uncomfortable joint sensation that they could ease 0:15:10.880 --> 0:15:14.880 only after repeated clicking. So it would be like, you know, 0:15:15.320 --> 0:15:18.360 popping your neck multiple times to get relief in your neck. 0:15:18.920 --> 0:15:22.360 And then there was another case study that described improvement 0:15:22.520 --> 0:15:26.000 with this dopamine drug and the fidget spinners. 0:15:27.040 --> 0:15:30.280 Yes, you can take a drug to stop cracking your knuckles. 0:15:30.760 --> 0:15:32.520 Look at to why that works in a little bit. 0:15:32.880 --> 0:15:35.080 But first I wanted to ask doctor Godwin what he 0:15:35.240 --> 0:15:37.880 thought was going on in the brain when we crack 0:15:37.920 --> 0:15:38.480 our knuckles. 0:15:39.560 --> 0:15:42.680 So it's not hard to reason out what might be happening. 0:15:43.080 --> 0:15:48.160 A reasonable hypothesis is that knuckle cracking can ride along 0:15:48.440 --> 0:15:51.440 on the same circus that the brain uses for habits 0:15:51.920 --> 0:15:55.160 in our normal lives. The habit system is a feature 0:15:55.560 --> 0:15:58.600 and not a bug. It takes actions that you repeat 0:15:58.680 --> 0:16:02.600 a lot, makes them fast and low effort. You don't 0:16:02.640 --> 0:16:06.720 want to consciously replan every step of tying your shoes 0:16:07.120 --> 0:16:10.640 or unlocking your phone or driving a familiar route, and 0:16:10.760 --> 0:16:14.000 so the brain chunks those behaviors into packages that can 0:16:14.080 --> 0:16:15.800 run with minimal supervision. 0:16:16.120 --> 0:16:19.040 I see, it's like the brain is made to put 0:16:19.120 --> 0:16:22.440 certain things into that category of automatic behavior. 0:16:22.600 --> 0:16:26.360 Yeah, it's very advantageous from an evolutionary perspective. If you 0:16:26.440 --> 0:16:29.360 were thinking about every action that you took, then it 0:16:29.400 --> 0:16:33.000 would be very difficult to navigate the world day to day, 0:16:33.480 --> 0:16:36.280 and it would be difficult if you were performing at 0:16:36.280 --> 0:16:38.600 a very high level in sports. For example, if you 0:16:38.720 --> 0:16:41.680 had to think about every placement of a golf club 0:16:41.760 --> 0:16:44.360 as you were making a swing. If you don't somehow 0:16:44.600 --> 0:16:48.760 make that more automatic, then you get into issues like choking, 0:16:49.040 --> 0:16:52.680 because that is kind of overthinking those kinds of behaviors. 0:16:53.320 --> 0:16:57.040 In other words, our brain is wired to form habits, 0:16:57.440 --> 0:16:59.720 and to form a habit, all you need is for 0:16:59.800 --> 0:17:02.200 you to do it several times and for it to 0:17:02.640 --> 0:17:03.200 feel good. 0:17:05.280 --> 0:17:08.520 So early in learning, the prefrontal cortex is more involved 0:17:08.600 --> 0:17:13.240 because you're deciding and evaluating. But with repetition, the control 0:17:13.359 --> 0:17:17.240 shifts toward the dorsal strainum and motor planning areas and 0:17:17.320 --> 0:17:21.320 the behavior becomes more automatic, and dopamine is involved in that. 0:17:21.440 --> 0:17:24.159 It's one of the signals that helps to stamp in 0:17:24.400 --> 0:17:28.159 a habit if it's producing either a rewarding outcome or 0:17:28.520 --> 0:17:31.680 a relief, and relief in some sense can be rewarding 0:17:32.040 --> 0:17:34.880 related to this sort of knuckle cracking behavior. 0:17:34.840 --> 0:17:38.360 Like if it somehow feels good, then your brain will 0:17:38.640 --> 0:17:39.639 want to keep doing it. 0:17:39.920 --> 0:17:42.680 Yeah, for knuckle cracking, the rewards is kind of this 0:17:43.160 --> 0:17:46.520 relief from stiffness or tension in the joint, and relief 0:17:46.760 --> 0:17:49.200 can be powerful because it teaches the brain that this 0:17:49.440 --> 0:17:52.959 movement fixes the sensation. So over time, the queue can 0:17:53.000 --> 0:17:55.880 be as subtle as a tiny joint feeling a moment 0:17:55.960 --> 0:17:58.479 of stress, or even just seeing your hands, and your 0:17:58.600 --> 0:18:00.840 brain is cued to add activate that loop. 0:18:03.080 --> 0:18:06.280 Yes, I know what you're thinking. If knuckle cracking involves 0:18:06.320 --> 0:18:09.560 the dopamine reward circuit in your brain, does that mean 0:18:09.600 --> 0:18:14.280 that it's like an addiction. Not quite. According to doctor Godwin, 0:18:14.520 --> 0:18:17.760 knuckle cracking doesn't quite rise to the level of an addiction, 0:18:18.280 --> 0:18:20.719 but it can become a compulsion. 0:18:22.800 --> 0:18:25.639 What distinguishes a habit from a compulsion. As a habit, 0:18:26.000 --> 0:18:28.600 you identify it, you know it, and you can stop it. 0:18:29.080 --> 0:18:29.240 Right. 0:18:29.480 --> 0:18:32.320 It's something that you can interrupt or distract yourself from. 0:18:32.800 --> 0:18:36.159 The compulsion is a feeling that's almost overwhelming that you 0:18:36.440 --> 0:18:40.760 must complete the act. It's very much the similar brain circuit, 0:18:40.880 --> 0:18:44.159 but in the case of compulsive behavior, the dopamine stamp 0:18:44.480 --> 0:18:45.840 is more profound. 0:18:46.119 --> 0:18:46.520 I see. 0:18:46.960 --> 0:18:49.600 But for the most part, there's no reports in the 0:18:49.680 --> 0:18:52.760 literature that knuckle cracking fits into a category that would 0:18:52.880 --> 0:18:54.200 identify it as an addiction. 0:18:54.600 --> 0:18:54.960 I see. 0:18:55.160 --> 0:18:57.440 There may be somebody out there that has a knuckle 0:18:57.520 --> 0:19:01.000 cracking addiction. You can't just disclaim that or disprove that, 0:19:01.560 --> 0:19:03.760 but I would say that it would be pretty rare. 0:19:04.240 --> 0:19:06.159 You'd call him a real knucklehead. 0:19:05.920 --> 0:19:08.240 Yeah, or a crackhead. Knuckle crack head. 0:19:08.600 --> 0:19:12.680 I know, I might get in trouble for them. Now. 0:19:12.800 --> 0:19:15.440 The good news for knuckle crackers out there is that, 0:19:15.680 --> 0:19:19.159 as far as anyone knows, popping your joint is not 0:19:19.320 --> 0:19:22.240 that bad for you. In nineteen ninety eight, a doctor 0:19:22.359 --> 0:19:26.320 named Donald Unger from Thousand Oaks, California published the letter 0:19:26.440 --> 0:19:30.240 in the journal Arthritis and Rheumatology, in which he reported 0:19:30.320 --> 0:19:33.840 the longest running experiment on the subject of knuckle cracking 0:19:34.520 --> 0:19:36.960 since he was a kid. Doctor Unger had the habit 0:19:37.080 --> 0:19:40.560 of cracking the knuckles on his left hand, but only 0:19:40.640 --> 0:19:43.480 on his left hand, not his right hand, and he 0:19:43.600 --> 0:19:47.120 did it at least twice a day. Fifty years later, 0:19:47.520 --> 0:19:50.200 in a somewhat tongue in cheek case report in the journal, 0:19:50.640 --> 0:19:53.320 he was happy to report that after about thirty six 0:19:53.920 --> 0:19:58.000 five hundred knuckle crackings, neither of his hands head arthritis, 0:19:58.560 --> 0:20:01.560 and that there was no notice difference in the appearance 0:20:01.920 --> 0:20:06.080 or health of both hands. For that case report, doctor 0:20:06.160 --> 0:20:09.800 Hunger was awarded the two thousand and nine ich Noble Prize, 0:20:10.119 --> 0:20:14.160 which he happily accepted, saying, quote, after about sixty years 0:20:14.200 --> 0:20:17.119 of knuckle cracking to prove that it does not cause arthritis, 0:20:17.640 --> 0:20:22.359 perhaps I deserve some sort of award end quote. Now 0:20:22.520 --> 0:20:25.720 there have been a couple of larger studies. In nineteen 0:20:25.800 --> 0:20:29.080 ninety a couple of doctors from Mount Carmel Mercy Hospital 0:20:29.119 --> 0:20:32.800 in Detroit studied a group of three hundred participants, seventy 0:20:32.840 --> 0:20:36.240 four of which were knuckle crackers. They found that quote, 0:20:36.560 --> 0:20:39.720 there was no increased preponderance of arthritis of the hand 0:20:40.000 --> 0:20:44.240 in either group. However, habitual knuckle crackers were more likely 0:20:44.320 --> 0:20:48.320 to have hand swelling and lower grip strengths. Habitual knuckle 0:20:48.359 --> 0:20:52.240 cracking was associated with manual labor, biting off the nails, smoking, 0:20:52.520 --> 0:20:57.080 and drinking alcohol end quote. And In nineteen seventy five, 0:20:57.320 --> 0:21:00.399 two medical researchers from the University of son Kelvia, Bornia 0:21:00.720 --> 0:21:03.960 published the study in which they surveyed twenty eight elderly 0:21:04.080 --> 0:21:08.280 patients about eighty years old and twenty eight kids about 0:21:08.359 --> 0:21:11.280 eleven years old. They found that just as many kids 0:21:11.520 --> 0:21:15.639 cracked their knuckles as older people, although they do admit 0:21:15.720 --> 0:21:18.760 that some of the elderly patients couldn't remember if they 0:21:18.960 --> 0:21:22.280 cracked their knuckles. But more importantly, they found that the 0:21:22.359 --> 0:21:25.840 knuckles of the elderly patients who cracked their knuckles weren't 0:21:25.960 --> 0:21:28.880 just as healthy as the knuckles of the elderly patients 0:21:29.040 --> 0:21:33.440 who did not crack their knuckles. They concluded, quote, the 0:21:33.560 --> 0:21:37.520 data fails to support evidence that knuckle cracking leads to 0:21:37.680 --> 0:21:42.280 degenerative changes in the metacarpal falangeal joints. In old age, 0:21:42.960 --> 0:21:46.359 the chief morbid consequence of knuckle cracking would appear to 0:21:46.440 --> 0:21:50.600 be its annoying effect on the observer end quote. Yes, 0:21:50.760 --> 0:21:54.360 knuckle cracking can be annoying, And it turns out there's 0:21:54.400 --> 0:21:59.320 actually a name for this. I just have a side question, 0:21:59.600 --> 0:22:02.119 which is when I hear other people crack your knuckles, 0:22:02.160 --> 0:22:05.000 it gives me that sense of like, ew oh, what 0:22:05.240 --> 0:22:05.399 is that. 0:22:05.840 --> 0:22:08.879 Yeah, there's a condition called misphonia, and it's kin to 0:22:09.200 --> 0:22:13.600 the fingers on a chalkboard response, yeah, and sort of 0:22:13.760 --> 0:22:16.800 being grossed out by body horror, that sort of thing. 0:22:17.359 --> 0:22:21.000 And the idea I think is your brain might interpret 0:22:21.320 --> 0:22:25.920 the popping of bones and flesh as being something that is, 0:22:26.520 --> 0:22:30.040 from an evolutionary perspective, something to avoid, uh huh, And 0:22:30.200 --> 0:22:32.399 so you may be having a response to that. 0:22:32.880 --> 0:22:37.160 Oh wow, it's tapping into like a very primitive reflex 0:22:37.400 --> 0:22:37.840 in the brain. 0:22:38.320 --> 0:22:43.280 Maybe again, you know, there's no literature on this, you know, 0:22:43.359 --> 0:22:45.760 it's really interesting that what it does point out there's 0:22:45.800 --> 0:22:49.840