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Jaysin Trevino, Flickr // CC BY 2.0
Jaysin Trevino, Flickr // CC BY 2.0

Does Cracking Your Knuckles Really Give You Arthritis?

Jaysin Trevino, Flickr // CC BY 2.0
Jaysin Trevino, Flickr // CC BY 2.0

You’ve heard it before. You’re in a quiet room in among a gathering of people, and then—POP!—a little cracking noise rings out, followed by another, and another, and another. For some, cracking knuckles is a habit, while for others that little pop brings relief. And it's not just reserved for tough guys before they beat people up: Between 25 and 54 percent of all people crack their knuckles multiple times a day. But is the old wives’ tale true? Are these knuckle-crackers more likely to hurt their hands and gradually develop arthritis as they get older? 

In short, nope! Despite the rumor that kids constantly hear, it turns out there is no scientific correlation between cracking your knuckles and developing arthritis in your joints, which is when one or more of the points where your bones meet develop inflammation. 

When you crack your knuckles, you're actually doing more bursting than cracking. The popping noise you hear is caused by small bubbles bursting in your synovial fluid, a yolk-like substance that lubricates the areas between bones and reduces friction for ease of movement.

Here's how it works: When you make the motion to crack your knuckles—either by stretching your fingers or bending them backwards—you expand the joint. This causes the pressure between the joint  to decrease, as well as the ligaments that connect the bones and the joint capsule that holds all of it together. That depressurization causes gasses like carbon dioxide, nitrogen, and oxygen that are dissolved in the synovial fluid to form into little bubbles that rush into the empty space. As the joints settle back into place, the fluid also returns to its rightful place and pops those little bubbles, causing that recognizable cracking sound. 

The sensation of cracking your fingers feels good because the stretching of the joint also stimulates nerve endings found along the fingers; joints can’t be cracked more than once within 15 minutes to a half hour, which is about how long it takes for those gasses to dissolve back into your synovial fluid.

Among the scientific studies conducted to prove that there is no correlation between cracking your knuckles and osteoarthritis, one published in the Journal of the American Board of Family Medicine in 2010 found that, among a group of 215 participants between the ages of 50 and 89, arthritis was prevalent in about 18 percent of the people who crack their knuckles and in 21.5 percent who don't, making any correlation inconclusive. Probably the most entertaining study on the subject is by a Dr. Donald Unger who, inspired by his mother’s warnings as a child about getting arthritis by constantly cracking his knuckles, spent more than 60 years cracking only the knuckles on his left hand at least twice a day (in this case, the right hand served as his control). His finding, published in 1998 in a journal called Arthritis & Rheumatism, found there was no discernible sign of arthritis in his left hand as opposed to his right.

So don’t listen to what mom says, everybody—feel free to crack away!

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Big Questions
How Do Aerial Skiers Perfect Their Jumps?
Cameron Spencer, Getty Images
Cameron Spencer, Getty Images

If you've ever watched an aerial skier in action, you know that some of the maneuvers these athletes pull off are downright jaw-dropping—and you've probably seen more than a few of these skiers land on their rear ends at some point. The jumps are incredible, but they're also so technical that one seemingly insignificant motion can drop a skier on his or her tail.

Given that the skiers can fly up to 60 feet in the air and come down on a 37-degree grade, it seems like just going out and trying a new trick would be a good way to break your neck. That's why you'll need one unexpected piece of equipment if you want to start training for aerials: a towel.

Instead of perfecting their flips and twists over the snow, aerial skiers try out their new maneuvers on ramps that launch them over huge swimming pools. The U.S. national team has facilities in Park City, Utah and Lake Placid, New York that include specially designed pools to help competitors perfect their next big moves. The pools have highly aerated patches of bubbles in their centers that decrease the surface tension to make the water a bit softer for the skiers' landings.

If you're an aspiring aerial skier, expect to get fairly wet. New skiers have to make a minimum of 200 successful jumps into water before they even get their first crack at the snow, and these jumps have to get a thumbs up from coaches in order for the skier to move on.

This sort of meticulous preparation doesn't end once you hit the big-time, either. American Ashley Caldwell, one of the most decorated athletes in the sport, is competing in her third Olympics in Pyeongchang, but failed to advance past the qualifiers on February 15, as she wasn't able to land either one of the two triple-flipping jumps she attempted. Still, it's this very sort of risk-taking that has brought her to the top of her game, and caused friction with more than one of her past coaches.

"Why win with less when you can win with more?" Caldwell said of her competition mentality. “I don’t want to go out there and show the world my easiest trick. I want to show the world my best trick, me putting everything on the line to be the best.”

You can check out some of Team USA's moves in the video below:

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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Big Questions
Is There Really Such Thing As 'Muscle Memory'?
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iStock

Is there really such a thing as 'muscle memory'? For example, in the sense of your fingers remembering where the keys of the keyboard are?

C Stuart Hardwick:

Yes and no. There is no literal memory in the muscles, but the thing people call “muscle memory” exists, though the name is a misnomer.

A better name might be “subconscious memory,” as the information is stored in the brain, but is most readily accessible—or only accessible—by non-conscious means.

What “non-conscious” refers to here is the brain’s enormous capacity to train up what might almost be called “subroutines,” that exist outside our conscious experience. I like the term for this that at least one researcher in the field uses: “zombie agency.”

Zombie agents are non-conscious, or sub-conscious (in the literal, not the Freudian sense) that can do essentially everything you can do except make value judgments. So, for example, you don’t consciously know how to control your muscles in order to walk —in all likelihood, you wouldn’t know where to begin—but your zombie agents do, and they’ll take you wherever you want to go, dodging curbs and puppies, and “waking you” when appropriate to decide which babies to stop and kiss.

Zombie agents can be rather startling things. When you suddenly become aware that you’ve driven halfway across town in the direction of the office instead of going to the shoe store Saturday morning, you have zombie agents to thank. You “wake” as if from slumber, and with the frightening realization that you’ve been flying down the highway at prodigious speed while your mind was on other things. You feel as if you’ve been asleep, and in a way you have—but a very funny kind of sleep in which it is only the uppermost layer of abstract reason that is disassociated from the rest of conscious experience. Your zombie agents have been driving to work, responding to traffic, adjusting the radio, noting the check engine light, all the things you think of as “you, driving the car,” except the big one: deciding where to go. That part was on automatic pilot (which is another good way to think of this).

This is at the advanced end of the spectrum. Typing your friend’s phone number using “muscle memory” is at the other, but it’s the same phenomenon.

We didn’t evolve to remember phone numbers, so we aren’t very good at it. In fact, we are so bad at it, we invent all sorts of mnemonic devices (memory aids) to help us [in] relating numbers to words or spacial memory, either of which are closer to the hunting and gathering we are evolved for. The illusion of “muscle memory” arises because we are supremely well adapted to manual manipulation and tool-making. We don’t need to invent a memory aid to help us remember what we do with our hands, we only have to practice.

So the conscious mind says “dial Tabby’s number,” and our fingers—or more correctly, the zombie agent which learned that task—do it. Similarly, after sufficient training, we can do the same thing with tasks like “play a major fifth,” "drive to work,” or “pull an Airbus A380 up for a go-around.”

It feels like muscle memory because the conscious mind—the part you experience as being you—is acting like a coach driver, steering the efforts of a team of zombie agents, all harnesses to collective action. But it isn’t muscle memory, it's just memory—though it may be stored (or at least some of it) in the deeper, motor cortex parts of the brain.

This post originally appeared on Quora. Click here to view.

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