Researchers may know why your knuckles make a sound when the crack

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Why is cracking your knuckles so noisy? It’s a question researchers have been asking for 60 years, but one new study may have finally cracked the case.

A paper published in Scientific Reports on Thursday says that microscopic bubbles cause the loud noise when they pop. Your knuckles are surrounded by fluid, and when you stretch and move your joints, the pressure creates bubbles. When those bubbles collapse, a sound is produced.

The theory isn’t a new thought. But in 2015, researchers at the University of Alberta observed knuckles cracking in a MRI machine. They saw that bubbles were still visible near your joints after a sound was heard, and concluded that the noise was made when bubbles were formed, not when they collapsed.

The authors of the newly published study didn’t fully agree with the 2015 analysis, and think a mathematical model is more accurate than a MRI. Their three equations showed that only a partial bubble collapse is needed to make a sound, which explains why bubbles were still present in the MRI.

So it seems that mystery may finally be solved. But why some people find the sound of knuckle cracking annoying remains another question altogether.

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