Their conclusion? When you crack your knuckles, tiny bubbles of fluid in the joint do collapse, just like those hippie scientists in the 1970’s thought. However, their research uncovered one important detail: The bubbles only have to partially collapse to produce that pleasurable, yet annoying pop. This explains why those pesky microbubbles of fluid were still found in the joints after cracking.
But one question remains: How does the collapse of such tiny bubbles produce such a loud sound? It just does, man. The authors showed how the pressure released by the collapsing bubbles produced acoustic waves, which can be calculated by their mathematical model. Given the speed of the bubble collapse and the claustrophobic environment of bone and flesh, it’s possible to produce a crack that reaches 83 decibels. That’s loud enough to intimidate precisely three thugs before you get in a badass street fight.
It’s unclear if this research has a practical application, but hey, at least we understand the human body a little better. I’ll never become a knuckle-cracker, but there are times when I appreciate the sound. In 1993, the Wu-Tang Clan sampled the sound of cracking knuckles to create the beat for their classic song, “Bring The Ruckus.” That song is awesome.