Interval Exercise Boosts Fitness

Don't Sweat It

From the WebMD Archives

Feb. 25, 2002 -- If the image of a bobbing, straining you, pounding on the treadmill for a gasping half-hour at a whack, is interfering with your New Year's resolution to dispose of that extra holiday weight, don't despair. It turns out that exercising in short spurts may do you just as much good as sweating over the long haul.

A study from the University of Wisconsin-Oshkosh, in the October 2001 issue of the Journal of the American College of Nutrition, showed that three 10-minute bouts of exercise, and two 15-minute bouts, and one 30-minute bout were each just about equally effective in increasing aerobic capacity and reducing body fat.

W. Daniel Schmidt, PhD, chairman of the department of physical education and health promotion at the university and lead investigator of the study, which involved overweight female college students, says the study shows that exercise divided into several short periods had positive effects on both heart fitness and weight loss and was comparable to exercising in fewer, longer sessions. (The nonexercising control groups, incidentally, increased both body weight and body fat content over the 12 weeks studied.)

One catch: The students also followed a restricted-calorie diet. Schmidt says he is not sure that exercising in spurts is ideal for the treatment of obesity, since a diet must also be followed. But research done recently at Laval University in Quebec shows that this type of exercise -- the technique is called interval training -- can indeed rev up metabolism quicker than regular, constant aerobic exercise.

How It Works

When exercising, your body uses one of two systems to produce energy --the aerobic system and the anaerobic system.

The aerobic system uses oxygen to convert carbohydrates in your body to energy, and it can fuel long, sustained exertion. The anaerobic system, by contrast, grabs energy stored in your muscles in the form of glycogen to fuel short bursts of activity like sprinting or lifting heavy objects. This system doesn't draw on oxygen and only provides energy for brief activities. It also pours out lactic acid as a byproduct and causes that achy, used-up feeling.


According to the American Council of Exercise (, interval training may allow you to enjoy the benefits of anaerobic exercise without the burning muscles. It involves alternating high-intensity and lower-intensity exercise within a single workout. The Swedes have given it the name fartlek, which means, "speed play."

In the Laval University study, for example, participants alternated between 3 minutes of moderate-intensity step aerobics and 1 minute of high-intensity stepping, repeating the cycle eight to ten times.

According to Wayne L. Westcott, PhD, fitness research director at the South Shore YMCA in Quincy, Massachusetts, interval training is "absolutely the best" for both beginners and high-end athletes. "High-end athletes all train that way," he says. "It's not necessarily the easiest, but it is the best."

Heart and Mind Benefit

"The most important phase of exercise for heart health," Westcott explains, "is immediately after the bout of exercise -- the recovery period. In interval training, you get multiple recovery periods [as you switch to low-intensity bouts] and thus an enhanced heart response."

Another important advantage of interval training is that it can help combat boredom. "Go into the standard gym," Westcott says: "Everyone is walking on treadmills or riding exercise bikes. Although these are expensive machines with readouts of every kind, usually the dials are covered by a towel or newspaper. The exercisers don't want to know how much longer they have or how much farther they need to go. They are bored."

Contrast this, he says, with getting on the bike and setting it for the first 5 warmup minutes at 50 watts, then jumping to 4 minutes at 125 watts. "That's 4, not 30," he emphasizes. "It's hard but you can do it."

For the next 4 minutes, dial down to 75 watts. "Suddenly, this seems easy, almost fun," Westcott exclaims. "You start enjoying it, instead of waiting for it to be over." Then back to 125 watts! "You should do three sets of the 125, 75, then a cool-down of 50 watts."

Boost Your Immune System

How do you decide your maximum? "Most people exercise at 70% of their maximum heart rate," Westcott says. "You can use the talk test: At maximum, all-out effort, you should not be able to talk except to say yes or no. At mid-effort, you could probably utter a sentence or two. And at low, effort, you should be able to hold a conversation."


To interval train for 30 minutes on the treadmill, Westcott says, don't walk 3 1/2 miles per hour for 30 minutes but instead try doing five intervals of 6 minutes each. Begin with 6 minutes at 3 miles per hour, then 6 minutes at 4, then another 6 minutes at 3, then 6 at 4, and finally a cool-down of 6 minutes at 3.

This gives you the same workout--30 minutes at an average of 3 1/2 miles per hour--but with more work effort than your body would normally produce.

As an added benefit, you may even boost your immune system. Researchers at Texas Christian University in Fort Worth recently did a small study on 10 volunteers. Exercisers had significantly higher counts of immune cells, and that immunity was highest after the second round of bike riding.

Jean Lawrence is a medical journalist based in Chandler, Ariz.

Beth Israel Deaconess Medical Center. Reviewed for medical accuracy by physicians at Beth Israel Deaconess Medical Center (BIDMC), Harvard Medical School. BIDMC does not endorse any products or services advertised on this Web site.

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© 2002 WebMD, Inc. All rights reserved.


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