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Why Do Knuckles Crack? Engineers Calculate the Answer

Crack! (Credit: Kay_MoTec/Shutterstock)

Love it or hate it, knuckles crack.

For some the noise signals a welcome release, while others cringe at the thought of joints shifting about in their sockets. The sound itself, though, is still a bit of a mystery.

Snap, Crackle, Why?

Researchers have debated the source of the sharp pops for over a century now, and actually thought they had it cracked in the 1970s. The event was simply the sound of bubbles in the sinovial fluid between our joints collapsing, researchers concluded, the result of something called cavitation.

You experience cavitation every time you open a can of soda. The can’s contents, including the CO2 dissolved in the liquid, are under pressure, and when you release that pressure by opening the tab, some of the CO2 turns gaseous, forming bubbles. The same thing happens in our joints when we stretch them out a bit — the sudden expansion lowers the pressure and bubbles form, only to disappear when the pressure returns. Pop pop.

But that theory was deflated recently by the discovery that bubbles in our sinovial fluid persist even after a good cracking. If the sound came from them being compressed, they should all be gone. It’s a fairly intuitive explanation, too. We all know we can’t crack our knuckles two times in a row — it actually takes about 20 minutes to reset the system.

Popping Models

This is where Vineeth Chandran Suja comes in. He’s a PhD student at Stanford, and he studies bubble formation in lubricants. Normally this means industrial fluids, but his specialty applies equally well to the lubricating fluid that bathes our joints, and which is responsible for the cracking. The idea actually came to him while thinking of a topic for a class project, he says. Suja happened to crack his knuckles as he was thinking, and the idea popped right into his head.

Along with his former professor Abdul Barakat, of the University of California, Davis, Suja took a mathematical approach to the problem. The two start by modeling a cavitation bubble inside the sinovial fluid, and then watch what happens as it the pressure returns and it grows smaller. They were looking to see what kind of acoustic waves the bubble’s deformation would produce in order to match it with actual recordings of knuckles cracking. They published their findings Thursday in Scientific Reports.

This kind of modeling is actually ideal for the problem, Suja says, because current imaging techniques aren’t fast enough to catch the behavior of the bubbles in action.

“We realized that mathematics could provide us with this convenient third eye that is required to look into the dynamics of knuckle cracking extremely accurately,” he says.

Ultimately, they found that their model was able to reproduce the acoustic signals of knuckle cracking extremely accurately when they assumed that the bubbles collapse and deform but don’t disappear. The finding lines up with previous research assuming that the sounds come from cavitation bubbles while also explaining why they stick around.

“We show that a partially collapsing bubble could quantitatively reconstruct the acoustic spectra which is observed experimentally with knuckle cracking,” Suja says. “A sudden collapse in such an environment causes rapid variation in pressure, and that’s nothing but sound.”

And as for worries that constant knuckle cracking could lead to damage or pain down the road, Suja says their model doesn’t alter existing advice a bit — cracking your knuckles won’t cause any harm.

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Yet Another Study Says Vitamin Supplements Are Worthless

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Vitamin — the first four letters come from the Latin word for “life.” To sustain that, we need these organic compounds in small amounts, but it seems their purpose ends there.

New research reaffirms the counterintuitive notion that vitamin and mineral supplements aren’t the magical panacea we’ve been led to believe. It’s something that researchers have been finding for years, and a meta-analysis, summarizing the findings of 179 individual studies, published on Monday in the Journal of the American College of Cardiology found that most common vitamins provide precisely zero benefit to those taking them.

Non-vital Vitamins

Specifically, the study concluded that multivitamins, as well as calcium, and vitamins C and D are essentially powerless. They do no harm, but they might as well be placebos. These findings run contrary to popular wisdom, which instructs us to load up on supplements to reduce the risk of heart disease, cancer and premature death.

This isn’t the first time science has refuted vitamin worship. In 2013 a series of studies in the Annals of Internal Medicine, collectively including hundreds of thousands of participants, concurred that vitamins do not lead to any boost in health. In fact, the studies found that beta-carotene, vitamin E and possibly high doses of vitamin A actually slightly increase mortality.

The only supplement that may live up to its reputation, according to the new study, is folic acid. This, with or without vitamin B, may prevent cardiovascular disease and stroke.

The tradition of using vitamins and minerals for nutrient deficiencies dates back to 1747, when the British naval surgeon James Lind treated scurvy with citrus fruit, rich in vitamin C. Physicians routinely make such prescriptions, though usually only in cases where the patient has a demonstrated deficiency of a particular vitamin or nutrient.

Supplement Crazy

In recent years, though, we’ve come to view supplements as the gateway to general health and longevity. A Gallup poll in 2013 showed that 50 percent of Americans regularly take vitamins or multivitamins.

On the flip side, a comparison of Gallup polls in 1975 and 2016 reveals plunging public trust in the mainstream American medical system. This phenomenon may have contributed to the ascent of “natural” vitamin and mineral supplements.

But it probably also stems from rampant marketing and advertising. Thanks to the Dietary Supplement Health and Education Act of 1994, manufacturers don’t have to prove the to the Food and Drug Administration that their supplements work. They can claim their products work, though, as long as they keep it vague (“strengthens the body”) and don’t profess to truly treat anything.

Call it a healthcare failure, call it a marketing miracle. Either way, call a doctor before you pop another vitamin. Odds are they’ll tell you to stick to fruits and veggies.

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KNOW THE CAUSE: Lyme Disease and Fungus

Lyme Disease and Fungus

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Morgellons and Dope (Crack)

Even though this person in this video blog needs help with her drug addiction she shares her true story of being infected with morgellons. Everyone has their own way in dealing with this horrible disease. If you google Morgellons or resistant scabies mites you will come across forums of people questioning if some narcotic drugs could possibly get rid of these things. It’s not uncommon to hear individuals who gets high and complains about feeling bugs crawling all over them, biting them, etc. In reality in many cases it is true. Because of these narcotic drugs poisoning the system it drives them out of the body. Just as the same as if taking anti-parasitic drugs such as ivermectin.

Morgellons disease is a poorly understood condition characterized by small fibers, particles and bugs emerging from the skin. People with this condition often report feeling as if something is crawling on or stinging/ biting their skin.

In no way do we endorse or suggest in using any illegal substance to deal or attempt to get rid of morgellons or resistant scabies mites.



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