Wendell Petersen, 61, stopped running long distances after he suffered a herniated disk. Marti Devore, 53, abandoned stair climbers and treadmills when she aggravated an old hip injury. Marilyn Franzen, 52, gave up racquetball and triathlons after three knee operations. As Petersen, Devore, Franzen and any other middle-aged fitness buff can tell you, the older you get, the more you have to deal with creaky and painful joints. But the benefits of exercise--from lower blood pressure to improved mood--are just too great to pass up. So most people who want to remain active eventually learn to accommodate their aging bodies by changing sports or exercise routines.
There are, however, a few rules of thumb to keep in mind. Recent studies have taught exercise physiologists a lot about what combinations of physical activities work best at different ages. But the same physiologists also warn that you shouldn't get so hung up on the new advice that you abandon your old routines. "Anything is better than nothing," says Wendy Kohrt, a professor of medicine at the Center on Aging at the University of Colorado Health Sciences Center. "Whatever you will do to remain physically active is what I suggest you do."
Like most experts, Kohrt divides fitness activities into three broad categories. At the top of the list is cardiovascular exercise--anything that makes the heart beat faster. "No matter what your age--unless you have a truly unstable condition--getting your heart rate up several times a week is really important," says Miriam Nelson, an associate professor at the Friedman School of Nutrition Science and Policy at Tufts University. "That trumps everything." The other two major types of activity--strength training and stability (or balance) exercises--come into greater play as you get older. You don't necessarily have to do separate exercises for each category, especially when you're young. Indeed, some of the best physical routines--like Tai Chi or rock climbing--combine two or more approaches. But expect to change the mix as you move through the decades of your life.
TWENTIES. At this age, you should regularly be doing some moderate and some vigorous exercise. Basically, you want to break a sweat at least three times a week for at least 20 to 30 minutes. Don't slack off the other days of the week. Go for a walk, climb the stairsanything to elevate your heart rate a bit. Plan to do muscle-strengthening exercises at least twice a week. You can probably get away with fewer exercises that target your trunk muscles or stretch your tendons and ligaments, but avoid the temptation to ignore these altogether. Your natural sense of balance--which depends on muscles as well as nerves--begins to fade earlier than you might think, at about age 16.
THIRTIES AND FORTIES. At this point, you need to start getting more systematic about your physical routine. Grace and bursts of speed don't come quite as naturally as they once did. Women in particular need to focus on strength training--two to three times a week--in order to build muscle mass and preserve bone, which otherwise begins to get thinner. Make aerobic activity a daily routine, and if you haven't already, be sure to include stretching, flexibility and balance exercises in your regimen. This is the time when many runners, soccer players and racquetball enthusiasts start the switch to biking, rowing, figure skating or cross-country skiing.