Exercise: How much is enough?

Have you ever wondered how human beings lived 50 or 100 years ago, before the era of self-improvement, health consciousness, and product safety regulations? Back in more innocent times when people had unprotected sex, smoked unfiltered Camels during pregnancy, and then threw the resulting offspring, unseatbelted, into the back of a station wagon for a family outing ? how did anyone survive at all?

Well, for one thing, they didn't survive as long as we do. In 1900 people lived, on average, about 47 years. Antibiotics, vaccinations, and improved nutrition are responsible for most of our increased longevity. These, along with cardiovascular and cancer treatments, advances in surgical techniques, and public health efforts such as those targeting tobacco use have all made us live longer. But are we living better?

Though people lived shorter lives decades ago, they also lived fitter lives. Manual and farm labor, fewer cars, and no electronic gadgets meant that physical activity was an integral part of most Americans' school and work days, family and social lives. Now exercise is an "add on" - something we need to think about doing. Precisely because physical activity isn't a natural part of our lives anymore, deciding to embark on an exercise program may feel very daunting.

Your goal determines your exercise needs

A good place to start is to determine your goals. Ideally, exercise should be enjoyable for its own sake, which is why many people find learning a new sport, martial art, or dance to be a particularly good way to start and keep exercising. If the goal is better health, most forms, intensities, and durations of exercise will improve mood, digestive, immune function, bone strength, and, new data suggests, even brain function. A wealth of research reveals that 30 minutes per day in which about 1,000 calories per week are burned improves cardiovascular and overall health and extends life. But "30 minutes a day" isn't the whole story. Even less exercise - any exercise - is helpful.  There's evidence that dipping to as low as half the recommended amount can add years to your life, although more research is needed to confirm this finding. Also, up to certain limits, the more exercise you get, the better. A New England Journal of Medicine study found that the greatest gains, in terms of longer life and lowered risk for disease, come when you expend approximately 2,000 calories per week in some form of exercise, such as walking, gardening, or sports. In this study, sedentary men were 64% more likely to suffer a heart attack than their counterparts who exercised up to the 2,000-calorie level. This translated into an average two-year gain in life span for the most active group.

Aim to hit the 1,000-calories-a-week mark - which translates to about 10 miles of brisk walking a week. This amount of activity offers substantial health benefits, and you may want to stay at this level.

There is, however, a difference between the level of exercise required for health and that needed for weight loss and maintenance of weight loss. To maintain your weight and prevent creeping weight gain, the expert panel that devised the 2005 Dietary Guidelines for Americans recommends roughly 60 minutes of moderate to vigorous activity, such as brisk walking, on most days of the week. If you are overweight or obese, 60?90 minutes of moderate activity (less, if the activity is vigorous) on most days of the week is needed to sustain weight loss. Adding "unstructured" physical activity to your day - climbing stairs, walking from place to place, doing chores, even fidgeting - helps, too.

Not everyone is capable of vigorous exercise right from the start. Increasing your daily activity by pushing a loaded shopping cart through the grocery store or by climbing the stairs instead of taking the elevator is a good way to begin exercising if you haven't been active. Or, a few times a day, try walking for just five minutes out of each hour. Gradually add minutes to each of these short walking sessions to boost your endurance.

Eventually, if you want to lose weight, reach for the 2,000-calories-a-week target. If you're already hitting this mark and want to push further, the 2,000-calories-a-week target isn't an upper limit. But be aware that your risk for muscle and joint injuries grows at higher levels of exercise. A good guide to reasonable exertion: if you can talk easily while exercising, work harder. If you can't carry on a conversation at all, back off. When an activity becomes easy, boost the length of your workout or your speed. Some research suggests that "weekend warriors" who regularly burn through more than 1,000 calories in one or two exercise sessions a week do have a lower risk of dying than entirely sedentary men - that is, if they have no major risk factors. However, safety issues, common sense, and the bulk of research stressing benefits that flow from regular activity on most days of the week argue against adopting this pattern.

The Bottom Line

Thirty minutes of exercise on most days improves cardiovascular health, and 60 minutes most days is required for weight loss and maintenance of weight loss. Less exercise, even in 10 minute increments, is beneficial, but more exercise, especially if spread out over several days a week, is even better. Unlike our ancestors in the nineteenth century and earlier, most adults today will survive to old age. A few hours of exercise a week starting now will make those extra years a lot more fun.

Dr. Suzanne Koven practices internal medicine with a special interest in weight issues at Massachusetts General Hospital in Boston, and teaches at Harvard Medical School.

Exercise: A program you can live with
Hundreds of studies conducted over the past 50 years show that exercise helps you feel better and live longer.Exercise: A program you can live withanswers many important questions about physical activity, from how your body changes through exercise to what diseases it helps prevent. It will also help guide you through starting and maintaining an exercise program that suits your abilities and lifestyle. Throughout, you'll find advice on being a savvy consumer when it comes to fitness products, as well as useful tools and tips designed to help make exercise work for you.

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