With a one-in-three chance of developing osteoarthritis by age 30, and a 9-in-10 chance by age 75, it's easy to assume that stiff, sore joints are an unavoidable part of aging. The cartilage slowly wears away -- leaving bones to scrape against each other.

Not so, says Dr. John Bland of the University of Vermont College of Medicine. Cartilage may be lost to injury, genetic defects and disease, but normally it's far too slippery to wear out. And so long as some healthy cartilage remains, exercise may bring it back.

A dozen years ago, researchers at the National Institutes of Health got rabbit cartilage to reproduce slowly in lab flasks. At first the cells wouldn't make collagen -- the fibrous protein structure of ligaments, tendons and bones. Vitamin C solved that problem, and stirring things up speeded growth. Cartilage churned with magnetic stir reproduced 20 to 50 times faster.

Next, Bland and fellow researchers at NIH turned to humans and found no gross difference in reproductive capability between the cartilage cells of children and those of elders (65-84). With proper nutrition and a little "stirring," Bland figured, old cartilage ought to rejuvenate.

Sure enough, in almost two dozen cases, Bland has shown that cartilage may grow again. In one case, after a year of aspirin, vitamins and exercise, a bed-ridden professor, 85, was able to walk again.

Surgery might have been faster, admits Bland, but "nothing beats your own joints." In any case, to keep moving late in life, keep on the move now.