EXERCISE RECOMMENDATIONS. WHO MAKES THEM AND HOW MUCH IS ENOUGH TO KEEP FIT

The latest in a long line of recommendations regarding the amount of physical activity required for good health comes from the Institute of Medicine’s Food and Nutrition Board.

“Why don’t they make up their minds?” a client asks. “First they tell us 30 minutes a day is enough exercise, and now they’re saying 60 minutes. Why the big change? Who issues these exercise recommendations, and why can’t they agree?”

Recent exercise recommendations

The latest in a long line of recommendations regarding the amount of physical activity required for good health comes from the Institute of Medicine’s Food and Nutrition Board. This Board has been responsible for developing the Recommended Dietary Allowances (RDAs) for the past 60 years, and consists of scientists from Canada and the United States. Board members are leading researchers in the field of nutrition and are appointed by the National Academy of Sciences.

The National Academy of Sciences has three sister organizations: the Institute of Medicine, the National Research Council and the National Academy of Engineering. Together, the four are referred to as the National Academies. The Academies are a private (nongovernmental), nonprofit organization formed more than 150 years ago by a congressional mandate to advise the federal government on matters requiring scientific and technical expertise.

The Food and Nutrition Board’s latest report is called “Dietary Reference Intakes For Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein and Amino Acids” (September 2001). Because one of the primary topics of the report is energy balance, the scientists addressed the topic of physical activity. (Energy balance refers to the relationship of caloric intake to energy expenditure.)

The scientists who wrote these recommendations gathered information from numerous studies looking at the relationship between level of physical activity and health. According to these scientists, people who manage to avoid weight gain and the health problems associated with obesity get the equivalent of about one hour of brisk physical activity per day. The scientists thus recommended that healthy adults strive for this amount of physical activity to stay healthy. They emphasize that the 60 minutes may be broken into smaller amounts scattered throughout the day, and note that shorter periods of more vigorous activity may substitute for the 60 minutes of brisk activity. They define brisk as a walking pace of 4 mph.

The 30-minute recommendation

The previous 30 minutes of physical activity recommendation was issued by the Centers for Disease Control and Prevention (CDC), along with a number of other groups, including the American College of Sports Medicine. The CDC is a governmental organization in the Department of Health and Human Services. Its job is to develop and apply disease prevention and control activities to improve the health of the people of the U.S.

The 30-minutes-per-day recommendation was an effort to form a simple recommendation that could easily be followed by most healthy adults. The primary goal of this recommendation was to encourage people who are currently sedentary to get moving. Researchers believed that the data they studied showed that significant public health benefits would be achieved if sedentary people exercised for 30 minutes a day. The researchers never said that 30 minutes was ideal; they only said that 30 minutes was a minimum level that would still confer substantial health benefits when compared to a sedentary lifestyle. In fact, a similar report released soon after by the Surgeon General acknowledged that”for most people, greater health benefits can be obtained by engaging in physical activity of more vigorous intensity or of longer duration.”

To understand the 30-minute guideline, contrast it with previous exercise recommendations, which were quite complex. Before the 30-minute guideline, exercise recommendations included information about exercise intensities based on target heart rates. These accurate but detailed recommendations tended to overwhelm people unfamiliar with exercise science.

Who is right?

The 60-minute and 30-minute advocates are both right. Public health officials can take two different approaches to their work. The first is to study the scientific evidence and come up with the most accurate recommendations possible. The 60-minute advocates say that 60 minutes will have a better health return than 30 minutes. This is probably true.

However, another public health approach is to study the population, and try to figure out a recommendation that will actually be followed. Here is where the 30-minute advocates are coming from. Sedentary people may be more likely to try for the 30 minutes than for 60. If a recommendation seems impossible, people may not try itat all. Better to recommend a minimum — 30 minutes — that people might really do.

Then again, fitness professionals who design individualized fitness programs are right, too. Detailed exercise prescriptions for clients who want to maximize the benefits of their exercise programs can be designed by people who are familiar with exercise science. How helpful is exercise advice that comes in a “one size fits all” format? Simple advice is better than nothing, but most people want more than simple advice.

REFERENCES

Blair, S.N., and J.C. Connelly. How much physical activity should we do? The case for moderate amounts and intensities of physical activity. Medicine and Science in Sports and Exercise 67: 193-205, 1996.

Centers for Disease Control and Prevention, www.cdc.gov.

Food and Nutrition Board, National Academy of Sciences. Dietary reference intakes for energy, carbohydrates, fiber, fat, protein and amino acids. National Academy Press, 2002. This report may be accessed at www.nap.edu/ books/0309085373/html.

National Academy of Sciences, www.nationalacademies.org.

Pate, R.R., M. Pratt, S.N. Blair, et al. Physical activity and public health: A recommendation from the Centers for Disease Control and Prevention, and the American College of Sports Medicine. The Journal of the American Medical Association 273: 402-407, 1995.

U.S. Department of Health and Human Services. Physical activity and health: A report of the Surgeon General. U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, and the National Center for Chronic Disease Prevention and Health Promotion: Atlanta, Ga., 1996.

Barbara A. Brehm, Ed.D., is professor of exercise and sport studies at Smith College, Northampton, Mass.