By Ben Kallen

Interval training is the hottest thing in cardio these days, for good reasons. The fitness and fat-loss results you can get are more impressive than those you get doing "steady-state" cardio (in which you move at an unchanging pace), and your workouts can be shorter, too. That's because intervals let you exercise at a higher intensity than you could just about any other way. Interval training is also a lot easier to learn and do than many people think. Keep reading to see how you can Supercharge Your Cardio: 4 Simple Ways to Boost Your Intervals and your results!

All it requires is alternating periods of moderate activity with bursts of all-out exertion during the same exercise session. And since those higher-intensity sprints are relatively brief, you may hardly even notice the extra effort.

The benefits: faster weight loss, more endurance, better health

Interval workouts allow you to conquer what's known as the "stress adaptation response." When you keep exercising at the same level of exertion, your body quickly gets used to the effort, so it doesn't improve as much. That's why many aerobics plans don't give you the weight loss results and performance gains you want.

But when you add in short periods of high-intensity exercise—during which your heart rate is raised closer to its maximum capacity—your body is forced to use new muscle fibers, which continue burning extra fuel even during lower-intensity exercise. And interval workouts allow you to spend more time on these exercise peaks than you could if you tried to go all out without rest periods. As a result, you'll experience faster increases in cardio fitness, more efficient burning of carbohydrates and fat, and possibly a greater natural release of the human growth hormone.

Over the past few years, researchers have demonstrated a wide range of fitness and health effects from interval training:
  • More weight loss. A 2007 study conducted at the University of New South Wales in Australia found that overweight women who rode exercise bikes for 40 minutes three times a week lost three times as much weight—mostly in their legs and buttocks—if they alternated intervals of light- and high-intensity cycling than if they rode at a steady pace the entire time.
  • Faster fat-burning. In a 2007 Canadian university study published in the Journal of Applied Physiology, volunteers who did interval training on exercise bikes burned 36 percent more fat than others when they cycled at a moderate pace afterward.
  • More stamina. A 2005 study also published in the Journal of Applied Physiology found that after just 2 weeks of interval training, six out of eight moderately fit young men and women doubled the amount of time they could ride a bicycle before getting too tired to continue. Volunteers who didn't interval train showed no improvement.
  • Healthier metabolism. When adults with metabolic syndrome, a condition that can lead to diabetes, were tested at the Norwegian University of Science and Technology in Trondheim, Norway, those who did interval workouts on a treadmill improved their blood sugar and insulin response by a higher amount than those who exercised at a steady, moderate pace. They also raised their "good" cholesterol levels by 25 percent, while the other group members didn't raise theirs at all.
  • Better heart health. In a 2007 study published in the journal Circulation, heart-failure patients who did interval training three times a week for 12 weeks improved their aerobic capacity, artery function, and quality of life more than those who did moderate, continuous training.
Intervals made easy

Here are four simple ways to boost your fitness and fat burning with intervals.
  1. Take a HIIT. High-intensity interval training is a long name for a simple formula. If you like to use a treadmill, stationary bike, or elliptical machine as part of your overall fitness program, this method will improve your results and make the ride less boring. Here's all you have to do: Following a 5-minute warm-up, alternate 2-minute periods of medium-intensity movement (at about half your maximum ability) with 30 seconds at the highest possible intensity, in which you're going all out and breathing hard. Do this for about six cycles—the whole workout should only take around 20 minutes. (If you're using a heart rate monitor, you'll see that you'll be at about 80 to 90 percent of your maximum heart rate.) As with every exercise, stop if you feel any pain or discomfort.
  2. Turn your recreation into an interval workout. Whenever you're out hiking, running, or bicycling for fun, change things up by incorporating a few high-intensity intervals. From time to time, go as fast as you possibly can for 30 to 45 seconds. Then return to your normal pace. When you've recovered for least a few minutes, and don't feel winded anymore, do another sprint. Throw in a few of these intervals every time you go out, and you'll increase your cardio fitness and burn more calories, too.
  3. Up your effort. Most Beachbody® workout programs alternate periods of high intensity with periods of recovery—meaning they have intervals built right in, which is one of the reasons they work so well and yield quick results. (So you really don't have to know the science—just follow your DVD's instructions.) But if you want the best results possible, push as hard as you can during those periods of high-intensity cardio. Move a little faster and jump a little higher, to the point where you're breathing hard. But don't overdo it during the recovery periods. You'll need these slower times to let your body recuperate.
  4. Take it to the MAX. Shaun T's new INSANITY workout program takes traditional interval training and reverses it. Instead of going all out for a short period of high-intensity movement and then hanging back for a longer recovery period, MAX Interval Training has you work like crazy for long phases, with brief rest times in between. The upshot is that you can achieve incredible fitness gains in just 2 months. But there's a reason this twist on intervals is the exception rather than the rule—you have to be in good shape to begin with, and even then, you need to be willing to work much harder than with regular intervals. But if you can handle it, you'll probably end up fitter than you've ever been before.