By Matt McMillen
WebMD Health News
Reviewed by Louise Chang, MD
Oct. 12, 2012 -- Don't have time to exercise? That excuse no longer works. Increasing evidence, including new research presented this week, shows that even short workouts that include surges of very high intensity can boost fitness and potentially shrink the waistline.
In the new study, exercise physiology graduate student Kyle Sevits of Colorado State University and his team demonstrated that a mere 2.5 minutes of giving it your all on an exercise bike can burn up to 220 calories.
That doesn't mean that you can do an entire workout during a commercial break. Instead, those 2.5 minutes should be divided into five 30-second sprint intervals, each followed by a four-minute period of light, resistance-free pedaling. All told, that is less than 25 minutes, during which you will burn more calories than if you did 30 minutes of moderate cycling.
"You burn a lot of calories in a very short time," says Sevits. "Nearly all the calories are burned in those 2.5 minutes; you burn very few during the rest period."
He also points to additional benefits that come from interval training, including increased insulin sensitivity and glucose tolerance, both of which are important for overall good health.
"This kind of research could help motivate people to get fitter and burn more calories," says Heather Gillespie, MD, a sports medicine specialist at UCLA Medical Center in Santa Monica. She was not involved in the research. "It's a very small study, but it's very promising and adds more evidence to the benefits of interval training."
Sprinting in the Lab
For the study, Sevits and his colleagues recruited 10 healthy men with the average age of 25. For three days, the recruits prepared for the study by eating a strict diet based on their caloric needs so that the researchers could be sure they were neither overfed nor underfed. Then they were checked into the lab.
The rooms where they spent the next two days were outfitted with equipment that allowed the researchers to measure the number of calories each recruit burned during their stay. They stuck to the same diet while they sat in front of the computer or watched movies. On one of the days, though, they had to exercise.
The sprint interval workout went like this: After a two minute warm-up came 30 seconds during which each man had to pedal as hard and fast as he could against high resistance. Four minutes of relaxed riding followed. Then, he went all out for another half minute.
All told, the participants each did five bursts in which they pushed themselves to their limits. They each burned approximately 220 calories for their efforts.
Previous studies have shown that high-intensity interval training such as this can aid the heart, both in healthy people and in those already suffering from heart disease. But while its health benefits may be established, its effect on calories has been far from clear, according to the authors. This study provides preliminary evidence that this kind of exercise may help maintain a healthy weight and, potentially, help shed pounds.
Do Try This at Home -- With a Bit of Caution
Gillespie says that, like any workout, sprint interval training comes with caveats.
"Everybody's 100% is different," she says, so people should know their limits. "I want people to move, but I also want to prevent injury."
She points out that interval training on a stationary bike is a low-impact exercise, which means it's easier on the joints. People should be more cautious with higher impact exercises, like running, especially if they are overweight or obese.
Gillespie also cautions that no one should try to cram their workout into just a couple of minutes.
"You can't sustain that high intensity for 2.5 minutes, and the rest period is just as important as the workout," she says. "If you want, you can always check your email during those four minutes."
When it comes to reaping the benefits of interval training, Sevits says people face some significant hurdles.
"The biggest barriers are the difficulty of this type of exercise and maintaining the commitment to do it," says Sevits.
He says that working with a personal trainer, who can encourage their clients to really push themselves, may be a way to go.
"That kind of coaching can be really motivating," he says.
Beginners, Sevits continues, should ease into interval training.
"First, build up your endurance, confidence, and comfort on whatever machine you have chosen before you start to really push yourself, then toss a few sprints into your regular 30-minute workout."
And if you find yourself struggling to maintain your max for those 30-second sprints? Don't sweat it too much.
"In reality, there's a whole continuum of benefits to reap as you get closer to your max," says Sevits.
The study was presented in Westminster, Colo., at a joint meeting of the American Physiological Society, the American College of Sports Medicine, and the Canadian Society for Exercise Physiology.
These findings were presented at a medical conference. They should be considered preliminary as they have not yet undergone the "peer review" process, in which outside experts scrutinize the data prior to publication in a medical journal.
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