Shorter workouts, bigger benefits

Interval training can help your heart and boost your metabolism

Published: March 2013

Want to shorten your workouts while getting the same or even more benefits? Try interval training, a type of workout in which you alternate bursts of peppier exercise with slower-paced “recovery” periods.

Intervals make you work more efficiently; your overall intensity is greater, so the length of your workout can be cut by about 20 percent. Plus, that approach yields health benefits that are at least as good, and possibly better, than traditional exercise, research suggests. Those benefits include:

  • Protecting your heart. Interval training has been linked to improved levels of HDL (good) cholesterol, says Cedric Bryant, Ph.D., chief science officer at the American Council on Exercise. A recent review in the journal Integrative Medicine Alert concluded that intervals are as effective as continuous moderate exercise, “if not more so, for increasing maximum exercise capacity, improving insulin resistance and blood pressure, reducing body fat, and raising HDL.” And a large 2006 epidemiological study in Norway linked a single weekly session of high-intensity exercise with a significantly lower risk of cardiovascular disease over a 16-year span.
  • Boosting metabolism. Our bodies use different energy sources—like glycogen or ATP, a molecule that stores energy in your cells—during more intense movements. “Like a drag-racing car that uses all of its gasoline in seconds, these energy sources lead you to burn more calories while increasing your metabolism,” says Anthony Slater, a certified strength and conditioning specialist at Core Performance, a corporate wellness group in Norwell, Mass.
  • Increasing vigor. The older you get, the less time you spend running around, and that void is related to the age-related decline in the quality of life. “If you can train at higher intensities, then easier movements, like simply walking and talking with friends, will become much easier,” Slater says.
  • Controlling diabetes. “Interval training has been found to significantly improve insulin sensitivity in diabetes patients, encouraging tissue in the body to take up sugar from the blood more rapidly in response to insulin,” Bry­ant says. In a small 2009 study in the journal Clinical Science, three months of twice-weekly interval training reduced fasting glucose levels in obese teenagers more than other exercise approaches. The increased benefit was still apparent nine months later.

Working in intervals

Start by replacing one or two of your regular aerobic workouts (such as cycling, swimming, or walking) with interval sessions of the same activity. You should get short of breath and feel a burning sen­sation in your muscles during the “speed” phases, and they should be intense enough that you can speak only a couple of words immediately after them, Bryant says.

As you become accustomed to the program, you can add more high-intensity segments while shortening both the speed and re­covery periods. Eventually, you might be able to gradually adjust the length of the speed and recovery intervals until they’re equal. But experts suggest progressing slowly in the first month.

Note that high-intensity exercise of any type does increase the risk of having a heart attack or injuring your joints or muscles. But Bryant says that some adults with cardiovascular disease can safely do interval training in a supervised setting. But see a physician first if you’ve been diagnosed with cardiovascular disease or are at an increased risk. You may need a doctor-supervised maximal exercise test before starting.

A basic program

Think of how hard you exercise on a scale of 0 to 10, with 0 being at rest and 10 exerting yourself as as hard as you possibly can. Divide your workout into three chunks: warm-up, exertion and recovery, and cool down. For a basic program, try this:

  • Warm-up: Two to three minutes at an easy pace, at 2 to 3 on the intensity scale. 
  • Exertion: One minute at 6 to 8 on the intensity scale. 
  • Recovery: Three minutes at 4 to 5 on the intensity scale.
  • Repeat: Alternate between the speed and recovery phases five times.
  • Cool-down: During your final recovery, decrease intensity to 2 to 3 on the intensity scale.

You can adapt that basic program by pushing yourself harder during the exertion phase, but for a shorter period of time, and taking a longer time to recover. So you might alternate between, say, 30 seconds at a 9 on the intensity scale with four minutes at 4 to 5 on the intensity scale. 

You can also use your heart rate as a guide to your interval workouts. First, calculate your maximum heart by subtracting your age from 220. During the exertion phase of your workout, aim for about 85 percent to 95 percent of your maximum, and during your recovery phase aim for about 50 percent to 70 percent of it.

For a 55-year-old, for example, the maximum heart rate would be about 165 beats per minute, the exertion phase would be about 140 to 157 beats per minute, and the recover phase about 85 to 115 beats per minute.

Bear in mind that those numbers are averages; the figures for you might differ. To get a more accurate estimate for you, consider talking with a an exercise physiologist or personal trainer. And see our Ratings of heart-rate monitors for our advice on accurate models and how to use them.

Editor's Note:

This article first appeared in the monthly newsletter Consumer Reports on Health. 

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