Whether you are moving or walking with or without reason your joints are always susceptible to cracks and pops as you use them. Stretching your joints in ways that they do not often move is the most common method of cracking or popping a joint, but regular movement can do the same thing.
The specific cause for the cracking of joints is unknown but there are many suggestions including: small cavities of a partial vacuum form in the fluid within that then collapse causing a popping sound, the ligaments stretching, a release of a gas in the joints as they are moved, and the idea that two cartilage surfaces will bond together and then break apart when the joint is used.
One thing is certain; once you have a joint that cracks or pops it is likely to do so forever. Knees are especially susceptible to this as they carry almost the full weight of the body.
It is unknown to date if the cracking of joints, intentially or not, can cause any long term damage.
