Short, sharp bouts of exercise good for the heart

Short bouts of exercise can be just as effective at protecting the heart as longer workouts, but getting the heart rate up is a key factor as light activity offers no cardiac benefit, two new studies show (Circulation 2000;102:975-80, 981-7).

Physical activity has long been associated with a decreased risk of coronary heart disease. It has been unclear, however, whether the duration of exercise episodes was important and whether accumulated shorter sessions were as predictive of decreased risk as longer sessions, provided that the same amount of energy was expended in each instance.

In the two new studies the researchers found that even with relatively small amounts of physical activity, with an energy expenditure of only 1000 kcal (4.18 MJ) a week, the risk of coronary heart disease decreased by a fifth compared with people who did not take that amount of activity. It did not matter whether the person took their exercise in a few long sessions or more frequent shorter sessions.

The same group of investigators conducted both studies, exploring the effects of the intensity and duration of exercise on coronary heart disease. Data for the two studies were taken from the Harvard alumni health study, which has followed Harvard alumni who entered the university from 1916 to 1950.

In the first study, led by Dr Howard Sesso from the department of epidemiology at the Harvard School of Public Health in Boston, the researchers followed 12 516 men aged 39-88 from 1977 to 1993. They found that those who expended more than 1000 kcal a week in total physical activity reduced their risk of coronary heart disease by about 20%.

Overall, a lower but nonsignificant reduction in risk of 10% was seen for those expending 500-999 kcal a week, slightly less than the current exercise recommendations of the United States Surgeon General.

Additionally, the researchers found that vigorous activity was also predictive of a reduction in risk. "Moderate and light activities, which may be less precisely measured, showed nonsignificant inverse association," the article said. The subject's heart rate needed to be raised more than 75% above baseline, so if a person's heart rate was 60, he or she needed to raise it above 105.

In a second study, led by Dr IMin Lee from the Department of Medicine at Brigham and Women's Hospital and Harvard Medical School in Boston, the researchers again found that physical activity was associated with about a 20% decrease in the risk of coronary heart disease.

This study followed 7307 men with an average age of 66 from 1988 to 1993. The researchers found that shorter sessions of physical activity were just as beneficial in decreasing the risk of coronary heart disease as one longer, continuous session of exercise, as long as the total calorific expenditure was equivalent.

Scott Gottlieb, New York


studentBMJ 2000;08:347-394 October ISSN 0966-6494