Thank Australopithecus for standing upright more than three million years ago and making possible such great human achievements as the four-minute mile, the 360 dunk, and the Eddie Van Halen guitar solo. Of course, A-Man also sentenced our knees to an eternity of trouble: clicks, creaks, tweaks, tears, and pops that can make bipedalism look downright backwards. Considering all that this joint does for us, it's no surprise that knee problems—some 9.5 million annually in the U.S.—are the leading reason people see orthopedic specialists. That said, there are ways to avoid visiting the doc. Follow our guide to proper care and maintenance, including training and rehab secrets of the pros, and you'll stay in the game longer and stronger. Your knees have evolved nicely over the eons; it's high time the care you give them catches up.