A few butt-squeezes here, a few stomach crunches there. Could intermittent exercise really be as effective as a full 30-minute workout in one sitting?
Yes, say Harvard researchers, reporting in the current issue of Circulation, the journal of the American Heart Association. As long as the total energy expended is the same, it may not matter whether you divide your workout into short bursts throughout the day or complete it in one marathon session, they determined.
Previous research has found that discontinuous workouts can improve fitness and cholesterol levels, but it was unclear whether the long-term risk of heart disease would be lower as well.
To find out, researchers, led by epidemiologist I-Min Lee at the Harvard School of Public Health, studied 7,307 male Harvard alumni from 1988 to 1993, tracking the amount of time the men exercised, played sports or simply climbed a flight of stairs in the course of a year.
The study looked only at men in their 60s, but researchers said they plan to study whether the effect holds true in women as well.
Heart Disease Unaffected Researchers found the risk for coronary heart disease was the same whether the men exercised in several short periods throughout the day, or completed their workouts in one time period, provided the energy output was the same.
“Physical activity does not have to be arduously long to be beneficial,” says Howard D. Sesso, an epidemiologist at the Harvard School of Public Health and a co-author of the report. “Short sessions lasting 15-minutes long appear to be helpful. If you are unable to set aside 30 minutes all at once for exercise, try two 15-minute sessions.”
The findings challenge the mantra once touted by many workout mavens, which states you need at least 20 continuous minutes of sweat-inducing intense activity three times a week, or 30 continuous minutes of moderate activity daily to get any health benefits.
“Intense” activities include tennis and running, while more “moderate” activities might include yard work, social dancing or golfing.
But in the last decade, experts have come to believe the body benefits even if the exercise is divided up into smaller blocks of time.
Guidelines Changing Several organizations are now advising notoriously lazy Americans, a quarter of whom currently get no regular exercise whatsoever, that if they can’t work in a full half-hour workout daily, shorter spurts of exercise can be equally as effective.
The Surgeon General’s new “Healthy People 2010” report notes that “while moderate physical activity for at least 30 minutes is preferable, intermittent physical activity also increases caloric expenditure and may be important for those who cannot fit 30 minutes of sustained activity into their daily schedules.”
The American College of Sports Medicine in Indianapolis, Ind., also has declared that exercise can be intermittent. “Physical activity can be accumulated through the day in shorter bouts of 10-minute durations,” its 1998 position paper on exercise states, so long as the total energy output is the same and a “minimum threshold of intensity” is reached.
How Little Is Too Little? But it is still unclear, researchers themselves admit, what that minimum threshold is.
Would a two-minute muscle flex done 30 times a day really equal an hour of working out?
“How long does the workout have to be [to have an effect]? We don’t know,” says Dr. Richard Stein, professor of medicine at the State University of New York, Health Science Center at Brooklyn and chief of cardiology at the Brooklyn Hospital. “Most people think 15 minutes. But could we do 7 or 8 minutes?”
“You need to stress the system to build muscle or strengthen the heart,” explains Dr. Paul Thompson, director of preventive cardiology at Hartford Hospital in Hartford, Conn. “If you are sedentary, a short period may be enough to induce changes, but if you’re in good shape, a short period may do nothing.”
Younger people are also less likely to reach a necessary level of stress on their systems from a short period of exercise, Thompson suggests. The study’s findings — that heart disease did not depend on the duration of exercise — may not apply equally to younger people as it does to the older men used in the study.
Go Climb Some Stairs But Stein points out the study definitely shows people can benefit by incorporating short amounts of exercise into their day. “You can walk to work or climb a flight of stairs,” he says, “and get most of the benefits of a half-hour workout.”
Dr. Michael Fleming, a family physician in Shreveport, La., and speaker for the American Academy of Family Physicians in Leawood, Kan., notes the study does away with the most common excuse that he hears: “I don’t have time to exercise.”