Not all it's cracked up to be

HEALTH

The most popular thread on the online community Jointcrackers.com is titled "You name it, I can crack it". These adepts go way beyond the basic knuckle crack that so many of us indulge in.

Apparently the nose, spine, hip, knees and toes, and virtually every joint in between, are crackable. And it's not just number, there's also magnitude. One member asks: "Does anyone else get euphoric effects from cracking bones? The bigger the crack the better I feel."

How do joints crack? In a joint, the two (or more) bones are held together by connective tissue and ligaments. In between is a thick, clear synovial fluid, which acts as lubrication. As with all body fluids, this one too contains dissolved gases, mostly carbon dioxide. When you stretch the joint beyond its normal range of motion in order to crack it, the bones move apart and the tissue around the joint is stretched. This means that the volume of the joint cavity increases, and the pressure within it drops.

As it drops, the gases in the fluid come out, forming bubbles within the cavity (or "cavitation"). As the stretching continues, the pressure drops further "" until the gas bubbles finally burst with the characteristic pop.

After the pop is done and the pressure released, the gases slowly dissolve back into the synovial fluid. For most people, this "refractory period" lasts about 25-30 minutes. For a little while, the joint even enjoys a slightly greater freedom of movement, which is why a few guitarists and pianists crack their knuckles before playing.

The "euphoria" mentioned above may be due to the effect on nerve endings within the joints that monitor motion. When these sensors are stimulated, the muscles around relax, which may be responsible for the "looseness" and relaxedness after a good crack or a visit to the chiropractor.

Is joint cracking bad for you? Does it cause arthritis? There's very little scientific evidence to say for sure, but what there is suggests not. However, some frequent and long-term knuckle-crackers see joint-thickening, as well as some soft tissue damage and loss of grip strength.

Like nailbiting, knuckle-cracking is a nervous habit. So, to quit, either resolve your underlying anxiety or try behavioural therapy, such as twirling pens or coins "" or that old trick of snapping your wrist painfully with a rubber band every time you get the urge.