Whether you've been exercising consistently and reached a plateau or you haven't worked out since high school gym class, interval training might be your fitness fix. A 2007 Australian study found that women who used the method—which entails alternating between fast- and moderate-paced exercise speeds—for 20 minutes three days a week lost five times as much weight as those who exercised at a steady, fast speed for 40 minutes three days a week. Evidence also suggests that the method may increase good (HDL) cholesterol levels, improve cardiovascular health, stabilize blood sugar levels and jump-start metabolism.

Seattle-based exercise physiologist Elizabeth Quinn, MS, provides the lowdown on this super fat burning workout.

What is interval training? This method of exercise combines moderate-paced aerobic activity with short bursts of high-intensity or high-speed exercise.

Can you give an example? You might walk on a treadmill at 3.5 mph for five minutes, then switch the speed to 5.5 mph for one minute. Repeat this sequence three times, and you have a routine.

How does increasing speed increase the impact of the workout? The faster intervals stress the cardiovascular system. In response, your body recruits more muscle fibers—ones that don't get used at the moderate level.

What are some other benefits? It makes exercising less intimidating and more efficient. The thought of going for a 10-mile jog can be exhausting. With interval training, you can get a good workout in 20 minutes. It can be incorporated into any type of exercise—the elliptical machine, treadmill or stair stepper, swimming, walking—even strength training. And at any fitness level, you can do some variation.

Are there any risks? Interval training can significantly stress the body. To get stronger, you need to push yourself—but don't push beyond what your body can handle. If you have heart disease or joint problems or you haven't been exercising for a while, get clearance from your doctor first.          

Quinn's tips

  • Take precautions: Warm up thoroughly to avoid pulling a muscle. Cool down afterward to lower your heart rate. Stretch after exercising.
  • Start slow: Begin with one interval workout a week; work up to two—I don't recommend more than that. Begin at 30 seconds for the fast interval. Once you get used to that, progress to a minute or more. Same with the speed: Start at a speed that is challenging, but not too hard; increase over time.
  • Shake it up: You can mix different exercises. Alternate walking with jumping jacks or a set of push-ups, then return to walking. Have fun with it!