Disclaimer: Intense exercise increases the immediate risk of a heart attack.
In the long run, both regular and intense exercise decreases the risk of a heart attack,
Research is suggesting that high intensity interval training — what runners for years have called “fartleks” (which means “speed play” in Swedish) — is the most efficient way to increase cardiovascular strength.
As far as I know, there is no substantial research on what kind of ratio of interval training to rest is most effective.
Some excerpts and links to articles are included after this section.
Absolutely make sure you have medical clearance before engaging in interval training, and start out minimally.
from
The Doctor’s Heart Cure
Alan Sears, M.D.
When you exercise continuously for more than about 10 minutes, your heart adapts by becoming more efficient. It achieves this efficiency through downsizing. Long-duration exercise makes the heart, lungs, and muscles smaller so that they can go longer with less energy, but there’s a trade-off. The cardiovascular system becomes very good at handling a 60-minute jog, but it gives up the ability to provide you with big bursts of energy for short periods. Far from protecting your heart, this loss makes you more vulnerable to a heart attack.
Dr. Stephen Seiler recently compared 20 minutes of running on a treadmill to running for 2 minutes followed by 2 minutes of rest for five cycles. He reported at the American College of Sports Medicine that interval exercise improved maximal cardiac outputs while continuous exercise did not. Intervals also produced another important improvement not seen with continuous exercise, the development of quicker cardiac adjustments to changes in demand. The interval trainees also achieved “higher peak stroke volumes.” Think of peak stroke volume as the horsepower of your heart. It is the highest volume of blood your heart can pump per beat when challenged
New York Times
Can You Get Fit in Six Minutes a Week?
Gretchen Reynolds
June 24, 2009
A few years ago, researchers at the National Institute of Health and Nutrition in Japan put rats through a series of swim tests with surprising results. They had one group of rodents paddle in a small pool for six hours, this long workout broken into two sessions of three hours each. A second group of rats were made to stroke furiously through short, intense bouts of swimming, while carrying ballast to increase their workload. After 20 seconds, the weighted rats were scooped out of the water and allowed to rest for 10 seconds, before being placed back in the pool for another 20 seconds of exertion. The scientists had the rats repeat these brief, strenuous swims 14 times, for a total of about four-and-a-half minutes of swimming. Afterward, the researchers tested each rat’s muscle fibers and found that, as expected, the rats that had gone for the six-hour swim showed preliminary molecular changes that would increase endurance. But the second rodent group, which exercised for less than five minutes also showed the same molecular changes.
The potency of interval training is nothing new. Many athletes have been straining through interval sessions once or twice a week along with their regular workout for years. But what researchers have been looking at recently is whether humans, like that second group of rats, can increase endurance with only a few minutes of strenuous exercise, instead of hours? Could it be that most of us are spending more time than we need to trying to get fit?
NPR
Interval Training: Good Exercise For All Ages
Allison Aubrey
August 24, 2009
The fitness boot camp craze is evolving. It’s no longer just the crack-of-dawn, sergeant-led calisthenics classes.
Moms meet three times a week at a local synagogue — and many of them bring their kids along. “They have a built-in play date while we exercise,” says instructor Kristine Oleson.
To maximize the hour-long class, Oleson incorporates a lot of short bursts of high-impact cardio. There’s skipping, jumping rope and running in place.
“Pick up your intensity,” Oleson calls out to her class of about 30 moms as they move through a round of skipping. “Really push it!”
The goal is to get heart rates up to about 85 percent of maximum for short clips of time, and then dial back down to a slow or moderate pace.
“The benefit of interval training is that it’s a very efficient way to increase your fitness quickly,” says researcher Tim Church of the Pennington Biomedical Research Center.
Church says intervals aren’t just for athletes and fit moms. Increasingly there’s interest in building them into the routines of older folks and those with chronic conditions such as diabetes or heart disease.
“This is really a hot area of research,” Church says. Preliminary studies suggest there’s an additional benefit — beyond the benefits of steady-paced exercise — to mixing in some interval training.
Researchers in Australia have tried to find the most effective pacing for interval training. They’re focused on bringing the approach to folks who are pudgy around the middle and older than 40.
“Everybody can do 8-second sprints,” says Steve Boutcher, a professor of exercise science at the University of New South Wales.
His studies have documented the benefits of 20-minute workouts on stationary bikes. Participants cycled three times per week. They alternated between 12 seconds of slow, gentle peddling and 8-second intense sprints, peddling as hard as they could.
“In the 20-minute bout,” Boutcher says, the actual hard exercise totaled just 8 minutes, “so it’s not that much exercise.” But the payoff was significant.
Over the course of four months, participants lost an average of 6 pounds of body fat. By comparison, those who cycled at a steady pace for 40 minutes, without mixing in the interval sprints, lost less than 2 pounds.
Researchers are not certain how to explain this difference. But Boutcher is studying the role of chemical compounds called catecholamines.
Boutcher says our bodies seem to produce higher levels of catecholamines during sprint-type exercises that elevate the heart rate.
“These are hormones that tell the fat cells to release their fat,” Boutcher explains.
If cycling doesn’t interest you, Boutcher’s advice is to try swimming, rowing or stair-climbing. If you like to walk, throw in some hills at a faster clip — anything to mix up the pace.
But it’s also important to recognize your limits, and to start out slowly.
“I’m a huge supporter of interval training because I think the payoffs are great,” Church says. “I mix them into my workouts on a weekly basis.” But he cautions that people need to be careful.
“We see men who are 45, and they’ve been sitting at a desk for the last 15 years, and they want to start doing their high school football workouts again,” Church says. They don’t realize how out of shape they may be. Church advises people to check in with their physicians before starting any intense interval training, especially those who are managing a chronic condition.
After years of running, mostly at a steady pace, the interval approach emphasized at Mommy Bootie Camp is paying off for one regular in the class.
“I think it increases stamina, and it does seem to help with weight loss,” says Kathleen Sylvester, who brings her two preschool-age children with her to class.
She says interval training has also helped her build long, lean muscles. One other reason she keeps coming: The baby-sitting is built-in
