Gabe Mirkin, M.D.

In 1490, Ponce de Leon set out to find the fountain of youth. He didn't find it, but all that walking may have helped him. The best way to keep yourself young is to exercise intensely once or twice a week.

All tests that are used to measure aging actually measure physical fitness. Scientists measure aging with a test called VO2max, your maximal ability to take in and use oxygen. Studies from Ball State University, Courtland State, Washington University in St. Louis and Mt Sinai Medical Center in Milwaukee all show that intense exercise maintains fitness. People who do not exercise lose 15 percent of their fitness per decade, those who exercise at low intensity lose 9 percent, while those who exercise intensely barely lose any fitness at all. At age 50, former Olympian Fred Wilt was able to run two miles in less than ten minutes, just by running five to seven miles a week and alternating almost flat-out 200 meter runs with jogging until recovery. His five to seven miles a week don't even compare to a world-class runner's more than 100 miles a week.

With increased intensity comes an increased risk of injury. Before you start an intense exercise program, check with your doctor. Realize that older people can't train intensely very often. If you go out and run alternate very fast and slow 200 meter runs on one day, you may have to wait for 2 to 10 days before you can run very fast again. The best way to maintain fitness with aging is to exercise very intensely in one sport on one day and then for the next few days, go very slowly or try another sport before you try to exercise intensely again in the same sport.