Joints are lubricated with synovial fluid. Studies suggest that everyday movements can cause volume and pressure changes within this fluid that lead to some of these familiar sounds.
Synovial fluid contains gases like nitrogen, oxygen, and carbon dioxide.
Volume Increases, Pressure Decreases, Gas Bubble Forms
Volume Decreases, Pressure Increases, Gas Bubble Collapses
While the exact causes of joint cracking and popping sounds are not well understood, it is commonly thought that the collapse of gas bubbles could be the source.
Fun Fact: After a joint cracks due to volume and pressure changes, it takes about 20 minutes before that joint can be cracked again. The joint needs time for the volume and pressure to reset.
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