Do you frequently pop your knuckles? Scientists may have finally discovered why the common habit produces the distinctive popping sound, according to a new report.
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Researchers from institutions in the United States and Europe recently conducted a study, published in Scientific Reports, to investigate the crackling noise you hear when adjusting your joints.
"When we crack our knuckles we're actually pulling apart our joints, and when we do that the pressure goes down. Bubbles appear in the fluid, which is lubricating the joint - the synovial fluid," lead author Abdul Barakat explained to the BBC. "During the process of knuckle cracking there are pressure variations in the joint which causes the size of the bubbles to fluctuate extremely fast, and this leads to sound, which we associate with knuckle cracking."
A previous study from the 1970s concluded that the collapse of the bubbles causes the cracking sound. However, the latest research proves that the bubble is still present and the pressure of a partial collapse is enough to generate sound.
Using a mathematical model, which matched the size of the bubbles to the ones that made sound, they were able to accurately predict the acoustic wave produced by the pressure of the bubble collapses.
“The model also shows that only a partial collapse of the bubble is needed to replicate the experimentally observed acoustic spectra, thus allowing for bubbles to persist following the generation of sound as has been reported in recent experiments,” the authors wrote in the study.
The scientists now hope to continue their investigations to simulate the inception, terminal and long-term behaviors of the bubbles to better support their findings.
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