Why do our knuckles crack?

Ever wondered what causes that loud popping noise when you crack your knuckles or stretch your joints? Watch our video to find the answer…


By pulling on a knuckle, you gradually increase the space between the bones. As there is only a certain amount of fluid around the joint to fill this volume, the pressure drops, which allows gases that were dissolved within the fluid come out of the solution and form their own little bubbles or cavities. As the finger is slowly pulled from the joint, a separation forms in the small gas-filled cavity. What the results show is that it’s actually the formation of the bubble that produces the cracking noise, rather than the bubbles popping.

Find the answer to more curious questions in How It Works magazine. Order it in printdownload it onto your digital device or subscribe today to ensure you never miss an issue!

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