EXERCISE
April 2, 2009

A Simple Exercise Guideline

A new study offers guidelines for knowing whether you've walked enough to serve as a moderate level of exercise.

If you've been putting off exercising because the guidelines are too confusing, a simple one has emerged for walkers. It recommends walking at a rate of 100 steps per minute for 150 minutes a week. No more excuses.

The idea behind an exercise guideline is to tell you the minimum amount of exercise you need to stay healthy. Most guidelines agree that this amount is 150 minutes of moderate exercise per week. But what is "moderate" exercise? Therein lies the rub. It's different for each individual and depends on their unique metabolism and the lifestyle they've been leading. Yet it should be possible to find an easy-to-follow guideline that works for most people.

The lowest walking speed that qualified as moderate exercise was on average, 100 steps per minute.

A team headed by Simon J. Marshall, an assistant professor of exercise and nutritional studies at San Diego State University, thinks they've done it.

The truest measure of exercise is how much energy is expended while doing it. The San Diego team measured this in study participants who were walking on a treadmill. The participants wore pedometers, which measured their step rate. The amount of energy they were expending was compared to the number of steps they were walking per minute. The lowest walking speed that qualified as moderate exercise was on average, 100 steps per minute. In technical terms, this was the rate at which the walkers were expending 3 METs of energy — three times the energy expended while resting.

So walking at a speed of 100 steps a minute or more for 150 minutes a week should do the trick. One way to do this would be to walk at this speed in 30 minute sessions, five times a week. If you're just starting out, Marshall suggests first mastering walking 1000 steps in 10 minutes. Just go out and buy a pedometer first. Pedometers generally cost from $10 to $25.

While pedometers do vary a little in their accuracy, and the energy expended per step will also vary depending on your weight and fitness level (a postal carrier, who makes a living by walking, would probably expend less than average energy while walking at 100 steps per minute than an overweight, sedentary individual would probably expend more), these complications don't matter that much. The idea is to give a ballpark figure of the least amount of exercise you need to stay healthy. You should try to be sure that you're in the ballpark. Fine tuning of an exercise program comes later.

What is moderate exercise for activities other than walking? David Katz is director of the Prevention Research Center at Yale University School of Medicine. His thoughts: "Our advice has long been that 'moderate' is a pace that noticeably increases heart and breathing rate while still leaving you capable of speaking in complete sentences. No pedometer needed."

The study was of 58 women and 39 men, average age 32. During treadmill walking at various speeds, oxygen consumption was monitored and later converted into energy usage.

The results of the study will appear in the May 2009 issue of the American Journal of Preventive Medicine.

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