By Gretchen Reynolds, NY Times, July 25, 2012
“Every four years, the summer Olympics get people excited to exercise,” says Glenn Gaesser, a professor and director of the Healthy Lifestyles Research Center at Arizona State University, who oversaw a new study about exercise and high blood pressure that was inspired in part by the coming games in London.
The streets and gyms fill with people who, fueled by stories of Olympic success, “run or work out for an hour or more,” Dr. Gaesser says. But “within a few weeks, most people have quit” and resumed their sedentary lives. “We wanted to see if there were approaches to exercise that would fit more easily into people’s lifestyles, but still be effective” in terms of improving health, he says.
Specifically, he and his colleagues hoped to determine whether breaking up exercise into small, manageable segments performed throughout the day would work as well as one longer, continuous bout.
So he and his colleagues gathered a group of adult volunteers. Each was generally healthy, except for some early symptoms of high blood pressure, a condition called prehypertension.
High blood pressure is, of course, one of the primary risk factors for heart disease and stroke, and prehypertension is one of the primary risk factors for full-blown high blood pressure. Almost 70 million Americans have prehypertension, Dr. Gaesser’s study reports, with symptoms like an average daily blood pressure approaching an unhealthy 140/90 and a tendency for blood pressure to spike to unequivocally dangerous levels throughout the day.
Encouragingly, prehypertension is known to respond well to exercise. But many studies of exercise and blood pressure have employed moderate exercise sessions lasting for an uninterrupted 30 minutes or so per day, which is the commonly recommended standard for improving health.
Dr. Gaesser, however, asked his volunteers to walk briskly at an intensity equaling about 75 percent of each volunteer’s maximum heart rate for 10 minutes three times during the day. The sessions took place at 9:30 a.m., 1:30 p.m. and 5:30 p.m.
On a separate day, the volunteers completed one 30-minute supervised session of brisk walking in midafternoon, while on a final day, they did not exercise at all.
All of them wore cuffs that monitored blood pressure continuously for 24 hours at a time.
As it turned out, exercise was helpful in controlling blood pressure, but breaking up the workout into three short sessions was significantly more effective than the single half-hour session. “The fractionized exercise led to lower average 24-hour blood pressure readings,” Dr. Gaesser says.
It also resulted in lower blood pressure “load,” or the number of incidences during the day when a volunteer’s blood pressure spiked above 140/90. Lowering blood pressure load is important, he points out, because a relatively high load “seems to be an indicator that someone with prehypertension is likely to progress” to full-blown, clinically high blood pressure.
Over all, the results “are really encouraging,” he says. “For people who think that 30 minutes of exercise is too hard or takes up too much time, we can say, just do 10 minutes” three times during the day. And, conversely, if someone is tempted to dismiss a mere 10 minutes of walking as too meager to be meaningful, “it seems clear that, at least for blood pressure control, fractionized exercise is actually more effective” than a single 30-minute bout.
His work joins a small but compelling body of science suggesting that, for many purposes, short, cumulative exercise sessions are remarkably beneficial. A study published last year in PLoS One, for instance, found that in children and teenagers, repeated bouts of running or other physical activity lasting as little as five minutes at a time reduced the youngsters’ risks of poor cholesterol profiles, wide waistlines and above-average blood pressure readings as much as longer exercise sessions did.
Other studies have found that exercising sporadically throughout the day aids in weight control, particularly for older women. It also, in a few small studies, improved aerobic fitness among previously sedentary people as much as a single, longer workout did and, as a regimen, was more likely to be maintained over the long term.
But so-called fractionized exercise has its limits. “You’re not going to make it to the Olympics” based on three 10-minute walks a day, Dr. Gaesser says. “You’ll be healthier. You won’t be an athlete.”
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