Benefit Analysis

Americans are likely to ask not how much exercise they should get, but how little activity they can get away with,” says Dr. I-Min Lee, assistant professor of medicine at Harvard Medical School, with overtones of John F. Kennedy.

She should know: Last year, the Harvard University epidemiologist published a study that led some people to conclude that only vigorous exercise lengthened life spans. Lee (vigorously) refuted that conclusion in interviews, but it didn’t matter--those recalcitrant exercisers for whom “vigorous” might as well have meant “forget it” thought they had an excuse to hang up their Reeboks.

If you want to get the most bang for your exercise buck, follow these seven general guidelines, which apply to any kind of exercise. They’re based on the experiences of the leading researchers such as Lee and Patty Freedson, a professor of exercise physiology at the University of Massachusetts who focuses on measuring physical activity, fitness experts and coaches.

* Consistency Counts: The evidence is clear--physical activity is most beneficial when it’s pursued regularly over a lifetime. “Many of the effects of exercise are fairly short term. You can’t really put the benefits in the bank,” says James Sallis, a professor of psychology at San Diego State University concerned with motivation and physical activity. Measures such as your weight, blood pressure and even psychological well-being reflect whether you’ve exercised lately much more than whether you were active two years ago.

Consistency also reduces the risk of injury. Exercise sporadically, and you risk damaging unconditioned muscles. Make activity a daily habit and you’re less likely to shock your system. So make sure you exercise more days of the week than you don’t, and ideally try to do something every day.

* Big Muscles Matter Most: The amount of energy you expend each year directly impacts your long-term health, says Russ Pate, professor of exercise science at the University of South Carolina.

The surest way to expend lots of energy is to get your biggest muscles moving--they’re energy hogs.

That’s why exercise recommendations call for activities like brisk walking, cycling, swimming--even gardening. The latter best illustrates the principle here. Sit in one place picking weeds, and only your arms and hands get a workout. But rake, till, bend and lift, and the large muscles of your legs and trunk get involved, making them stronger and requiring more of the heart, lungs and circulatory system. When it comes to physical activity for a lifetime, make sure you’re using your largest muscles every day.

* Make It Weight-Bearing: You’ve got a choice: Hop on your bike, go for a swim or go for a walk. Which is better? Well, if there’s any chance of becoming one of the 24 million Americans affected by osteoporosis, the walk may be your best choice. That’s because weight-lifting can prevent osteoporosis and the most convenient weight to lift is your own body weight. Sallis calls weight-bearing exercise “jarring the bones.”

By any name, it means doing an activity in which your bones--not a bicycle seat or pool water--support your full body weight. It’s been shown to slow reductions in bone density late in life and even increase it in some instances. So when you have a choice, do your bones a favor and stay on your feet.

* Emphasize Low Impact: Discomfort and injuries are among the most common reasons people give for quitting physical activity. Pate puts it succinctly: “Pain is not positively reinforcing.” Yet he’s emphatic that exercise doesn’t have to hurt to be good for you.

In many cases, it’s the activity that causes the problem. For example, a University of Colorado study found that runners and walkers who exercised regularly at the same heart rate experienced comparable fitness gains, but the runners missed significantly more days due to injury. This isn’t surprising since the impact force in running is three times your body weight; in walking, it’s only one times your body weight. Ultimately, any activity is better than none, but if discomfort is getting in the way of consistency, go low impact.

* Try Variety: Varying the amount and intensity of your exercise can help in two ways: First, if your goal is not just health but also building fitness, variety can enhance your body’s response. For example, varied daily walks--occasionally throwing in harder and easier days--allows your body to adapt and rebuild on the easier days. Second, variety may help stave off boredom and keep your workout routine lively.

* You Get What You Pay For: The benefits of exercise come directly in proportion to the amount of work you put in. Exercise modestly but regularly for 30 minutes a day, and you’ll reduce your chances of heart disease and chronic illness. Crank up the duration of your exercise, and you’ll burn more calories, which can help control your weight. Increase your effort, breathing hard and raising your heart rate during several of your weekly outings, and you’ll garner improvements in cardiovascular fitness, further improving your outlook for health and longevity.

There’s no getting around the fact that your time and effort determine the results. But there’s good news in this: The less you’ve been doing until now, the more you stand to gain. “If you’re not very active,” Sallis says, “just adding a little bit of daily activity can have a substantial effect on your health.”

* Make It Work for You: There’s a fair amount of research on how important enjoyment is to sticking with physical activity, but Sallis quotes a real-life example, not data, in driving that message home.

“Just watch kids,” he says. “You don’t have to convince them to be active; if you call it playing, they’ll get out and do it.” Pate points out that it’s also important to pick out activities that are not just enjoyable, but that are also accessible. That way, you won’t have excuses such as traffic jams or long lines at overcrowded gyms.

A reinforcing environment is also important. “For some people, that’s solitude,” Pate says. “For others, it’s a socially supportive setting.” So be like a child, and make your daily walk playful. You’re guaranteed health for a lifetime--plus, you’ll have a lot of fun.

* Reprinted with permission from Walking, a Boston-based magazine.