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STEVE INSKEEP, host:

It's MORNING EDITION from NPR News. I'm Steve Inskeep.

RENEE MONTAGNE, host:

And I'm Renee Montagne. Good morning. In Your Health today, the science behind two different fitness strategies. We'll examine how elementary school kids can benefit from weight-lifting workouts. First, interval training. Athletes have done it for decades. Now, it's all the rage at fitness boot camps. NPR's Allison Aubrey reports on the latest research linking short, intense cardio sprints to weight loss.

ALLISON AUBREY: If you're out of the loop on the whole boot camp craze, it's basically just group fitness classes aimed at whipping people into shape. They're often held outdoors and at the crack of dawn. Much of this appeals to Kristine Oleson. But she decided to start her own mommy boot camp, she swapped a 5 a.m. start time for 10, rented a space in her neighborhood, and opened the doors to moms with their kids in tow. This way, moms wouldn't need to find a babysitter.

Ms. KRISTINE OLESON (Owner, Mommy Bootie Camp): No excuse. No nursery. No money. Bring the kids, and they play. And they have a built-in play date while we exercise.

AUBREY: The kids are sprawled all over the place. Some sit with coloring books and crayons. Others try to keep up with their moms. To maximize the impact of the exercise for the moms, Oleson incorporates lots of short bursts of high-impact cardio. They are skipping, jumping, and running in place.

Ms. OLESON: Pick up your intensity.

(Soundbite of music)

Ms. OLESON: Push. Out, in.

AUBREY: The goal is to get heart rates up to about 85 percent of maximum for just short clips of time, and then dial back down to a slow or moderate pace using the interval approach.

Dr. TIM CHURCH (Pennington Biomedical Research Center): The benefit for interval training is it clearly is a very efficient way to increase your fitness quickly.

AUBREY: Tim Church directs exercise and preventive medicine studies at the Pennington Biomedical Research Center. He says intervals aren't just for athletes and fit moms. Increasingly, there's interest in building them into the routines of older folks and even those with chronic conditions, such as diabetes or heart disease.

Dr. CHURCH: This is really a hot area of research. It is: Is there an additional benefit to mixing in some interval training? And the preliminary work really suggests there is.

AUBREY: So what would interval training look like for, say, middle-aged folks who are overweight? Researcher Steve Boucher of the University of New South Wales in Australia has done several experiments with this age group using 20-minute workouts on stationary bikes. He has participants start with 12 seconds of slow, lackadaisical pedaling, followed by short, eight-second sprints where they pedal as hard as they can. Then they alternate back and forth.

Professor STEVEN BOUTCHER (University of New South Wales): The eight-second sprint is doable by all the groups we've looked at - old people, you know, overweight people. Everybody, so far, we've tested has been able to do it. And in the 20-minute bout, the actual heart exercise is only eight minutes. So it's not actually that much exercise.

AUBREY: But Boutcher says the payoff is impressive. In one four-month study, participants improved both blood pressure and blood sugar readings. In addition, they lost an average of six pounds of body fat. By comparison, those who cycled at a steady pace for 40 minutes, without mixing in the interval sprints, lost three times less fat - not much at all.

Boutcher says he's not certain what explains this difference, but he's focused on certain compounds called catecholamines, which the body seems to produce at higher levels during sprint-type exercises that elevate the heart rate.

Prof. BOUTCHER: Catecholamines is the major chemical that induces fat burning. So these are hormones that really tell the fat cells to release their fat - and for other cells to burn the fat.

AUBREY: 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.

One mom who's become a regular at the boot camp, Kathleen Sylvester, says her approach to running used to be, set a steady pace and keep it. But with the interval classes, she's noticed a difference.

Ms. KATHLEEN SYLVESTER: I think it increases your stamina. I think it does help with weight loss. And it also helps develop long, lean muscles.

AUBREY: Which, Sylvester says, pretty much covers it.

Allison Aubrey, NPR News.

MONTAGNE: And you'll find a photo gallery of mommy boot camp at the new npr.org, where you can also sign up for the podcast of Your Health.

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