ORLANDO, Nov. 11 -- If you don't have time for a 30-minute workout each day, it may be just as good to divide the exercise time into several shorter-duration episodes a week of at least 10 minutes or longer, report scientists today at the American Heart Association's 70th Scientific Sessions.
That message comes from an evaluation of exercise habits of more than 22,000 men involved in a 12-year study of health behaviors of physicians. Researchers found that the risk of heart attack and death from heart disease declined steadily as the frequency of vigorous exercise increased from one to five times weekly. However, the benefits of physical activity did not increase further after 24 minutes per exercise period, says Claudia Chae, M.D., a research fellow at Brigham and Women's, who presented the findings at the meeting.
Physical activity has long been known to reduce the risk of heart disease and heart attack, but the relative importance of exercise frequency versus duration has remained unclear, says Chae.
In the study, men who exercised five or more times a week had 46 percent fewer heart attacks and a 44 percent lower risk of heart attacks and deaths due to heart disease, compared to men who exercised less often than once a week. During 12 years of follow-up, 716 non-fatal heart attacks occurred in the study, and 297 men died from heart disease, including fatal heart attacks. Chae and colleagues compared heart attack rate and heart disease deaths with the men's self-reported physical activity habits at the study entry and after three years.
Physical activity was defined in practical terms. "Literally, the men were asked how often they exercised vigorously enough to work up a sweat, and how long each exercise episode lasted," explains Chae.
The men were separated into four categories of exercise frequency: less than once a week, once a week, two to four times weekly, and five or more times a week. They also were separated into four categories of exercise duration: 10 minutes or less per episode, 11-24 minutes, 25-40 minutes, and more than 40 minutes per episode.
The risk of heart attack decreased by 36 percent among those who exercised one to two times a week, 38 percent for those who exercised more than three to four times a week, and 46 percent among men who exercised five or more times weekly. The combined risk of heart attack or death due to one or more heart attack decreased about the same amount.
The effect of exercise duration was greatest among men who worked out for 11- 24 minutes per exercise episode or longer. Men in that duration category had a 46 percent lower risk of heart attack and 35 percent lower combined risk of heart attack or death from heart disease, as compared to the men whose physical activity lasted 10 minutes or less. These benefits did not increase significantly for men who reported longer periods of physical activity.
"While frequency and duration of exercise both contribute to health benefits, these data suggest that how often a person exercises is a more important factor in terms of reducing the risk of heart disease," she says.
Since the study included only men, Chae says the specific results of the study are "not able to be generalized to women." However, the AHA recommends that men and women engage in physical activity on a regular basis.
The investigators calculated the benefits of exercise after statistically controlling for the effects of other factors, such as blood pressure, cholesterol level, smoking, alcohol consumption and use of aspirin. However, one limitation of the study is that it is based on self-reported information. The participants didn't actually time each workout.
Chae says the findings are consistent with recommendations of the American Heart Association which encourage frequent workouts that last 30 minutes or longer for three-to-four days per week, or more often.The Physicians' Health Study (PHS), initiated in the mid-1980s, has been accumulating data on the health and health behaviors of 22,071 male physicians, ages 40-84 years old when the study began. All the men were free of heart disease and cancer at the study's outset.
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