A new study has revealed that when you crack your knuckles, you actually create a gas bubble between bones of flexed joints. With this, science has reached one step closer to end the long-standing mystery of knuckle cracking.

The study also suggested that a prior speculation, according to which, a flash of light happens approximately 10 milliseconds after the sound is also right. To conduct the study, Dr. Robert Boudin from the University of California analyzed some people in two groups. First group had 30 men and women, who were confessed knuckle crackers.

The study researcher multiplied the number of years the participants had been cracking knuckles with an average number of cracks each day. After that, Boudin wound up the multiplied numbers with 33 to 800 crack-years per participant. Then, Boudin included ten more participants in the study who were also non-knuckle crackers.

After that, the participants were asked to crack the knuckle at every finger’s base, also known as metacarpophalangeal joint. At the same time, the researcher was scanning knuckle by ultrasound. In about 400 attempted trials, 62 produced the trademark crack.

Boudin said the bubble model is a good one. “There have been several theories over the years and a fair amount of controversy about what’s happening in the joint when it cracks. The cracking sound and bright flash on ultrasound are related to the dynamic changes in pressure associated with a gas bubble in the joint”, Boudin added.