The popping of small gas bubbles within joints -- not grinding bones -- are thought to be the cause of the cracking joints, such as those at the knuckles.

When pressure is applied to joints, especially knuckles, the dissolved gases in the fluids of the joint form a bubble which bursts, resulting in the characteristic cracking sound, explained Dr. Winfried Berger of Huntingdon Bone and Joint Surgery Inc.

While the gas bubbles may also cause some of the cracking from other joints, Berger attributed cracking of the more complex junctures like vertebrae or knee joints to the simple alignment of the bones and ligaments. Knowing the correct way to position the joints for the desired effect is also important.

For the most part, cracking joints is a matter of practice -- those who have been doing it longer are able to position their bodies in the best possible ways for the joints to crack. However, the lack of joint cracking ability can also be attributed to the elasticity of ligaments or stiff joints -- some bodies simply are not capable of joint cracking.

Berger also addressed the issue of knuckle cracking leading to extra knuckle growth, explaining that there is no real way to test that theory, making it nothing more than an unproven myth.

He said cracking joints can cause no real damage or lead to arthritis, nor is it truly helpful in any way.

"I don't think there is any benefit to cracking joints besides a temporary change in body sensation," he said, "and that's what people want when they crack joints, that changed body sensation."