Mom told you not to, but you went on cracking those knuckles anyway, didn't you, sport?
Cracking your fingers or (gag) toes, is simply you forming—then popping—an air bubble in your synovial fluid, the gooey stuff that gathers in the cavities of your digits and joints.
And while this oft-cited study found that the practice doesn't increase your risk of developing arthritis as you age, researchers did find that some (but not all) elderly knuckle-crackers have slightly weaker grip strength than non-crackers. That said, this study came out well before improving hand strength (via weights, golf, tennis-ball squeezing, etc.) became standard in geriatric care.
In short, while you risk skeeving out your cube mates, you digit crackers should be okay in the long haul.
—Mike Dawson is a magazine writer and editor and a regular contributor to Details.