Chances are, you don’t have hours to spend at the gym each day. But you know that you need to fit exercise into your busy schedule. So if you’ve had it with marathon workouts that cut into your precious time, you owe it to yourself to check out more efficient and effective types of exercise.

Recent research has shown that you can achieve huge improvements in fitness, health, and fat loss by spending no more than one hour in the gym each week. The secret? Interval training. Today, I’ll show you how you can use interval training to cut a 60-minute cardio workout down to only 20 minutes.

According to Canadian researcher Martin Gibala, Ph.D., “It only takes a few short bouts of intervals every other day to improve fitness levels. For the Type A person that doesn’t have the time for hours of exercise, this is some reassurance that they can still improve their fitness.”

If you think intervals are only for elite athletes, understand that even beginners can do them. “It is all related back to your individual fitness; exercise at a little higher intensity and then back off,” says Dr. Gibala. Interval training is based on subjective effort. Rather than insisting that you achieve a specific heart rate or running speed, it simply requires you to work at about 80% of your relative effort level for a short period of time … and then back down for some recovery.

So while intervals may mean a full-out running sprint for people with high levels of fitness, intervals can also mean walking at 4.0 mph for others. It’s a model of exercise that you can fit into at any fitness level. (At the end of this article, I’ll show you how even a sedentary individual can get started with walking intervals.)

By definition, an interval is a brief bout of intense physical activity – such as a sprint – alternated with a longer period of lighter exercise. For example, you might exercise hard for 30 seconds, then exercise lightly for 90 seconds. That’s one interval. Yet this rudimentary formula makes interval training the world’s most powerful form of exercise. In fact, interval training is equal to or superior to traditional cardio workouts in many ways.

The Pros

  • “Very intense exercise-training is extremely potent and time efficient,” writes Dr. Ed Coyle in the Journal of Applied Physiology. With intervals, the average person can achieve similar fitness levels as with traditional endurance training, but in 70% less exercise time.
  • You only need to do intervals every other day, so you have more days off. This is great news for men and women who want to spend more of their free time with their family or pursuing other interests.
  • Dr. Coyle suggests that intervals probably have “the same health benefits as regular aerobic exercise” (e.g., reduced cholesterol, reduced triglycerides, and improved insulin sensitivity).
  • Intervals are equally as effective as traditional endurance exercise at increasing muscle enzymes that may help prevent Type 2 diabetes.
  • Interval training results in greater fat loss than traditional exercise programs.
  • Time flies. Not only will you be able to reduce your training time, but the actual exercise component will zip by because of the alternating periods of intensity.

The Cons

  • Discomfort. Intervals are no walk in the park. While you don’t have to exercise at 100% intensity in order to see results, you will have to leave your “workout comfort zone” in order to achieve the benefits of high-intensity training.
  • Your legs will feel like jelly at the end of the workout. So don’t schedule an interval training session immediately prior to a full day of walking the floor at a trade show.
  • You will need to do an extended warm-up if you plan on running sprints for your interval training session. Explosive running can lead to injury if you are not prepared. If you run your intervals, try doing them up a hill. That should reduce the risk of injury.
  • Most people do interval training incorrectly. Because most people are set in a slow, steady frame of mind, they end up exercising too hard during the recovery interval period. If you do that, you are not going to be able to work as hard during the real interval. So make sure you exercise only lightly during the recovery period.

Interval training also allows us to bury myths such as the “fat-burning zone” and that “it takes 30 minutes of exercise before your body begins to burn fat.” While a lot of skeptics dismiss the potential fat-loss benefits of intervals because the workouts are so short, Dr. Gibala points out, “The calories burned in 20 minutes of intervals are the same as in 20 minutes of steady-state exercise at 70% of VO2max [maximum oxygen uptake].”

Another group of Canadian researchers, this time from Laval University (what’s with us Canadians and intervals, anyway?), found that 20 weeks of high-intensity interval training led to more fat loss than a traditional endurance exercise program.

As with any type of exercise, sedentary individuals should proceed with caution and consult with a doctor before beginning interval training. (I recommend that every sedentary person over 30 years of age have a complete physical before starting any exercise program.)

But intervals are not a heart attack waiting to happen. Since muscle fatigue is likely to be the weak link in your interval performance, “this may actually lower the total stress on your heart,” says Dr. Gibala. (Interval training has already been safely used in cardiac rehabilitation settings.) But, as always, train conservatively.

So how do you do interval training? Dr. Gibala suggests, “Simply use a resistance that causes fatigue in your leg muscles in about a minute.” Then take about a 75-second rest and go again. Repeat for six intervals … and you are done.

Here’s a sample program for an absolute beginner (someone who could walk for 30 minutes at 3.5 mph):

Step 1. Warm up: Five minutes of walking at 3.5 mph.

Step 2. Speed up and walk at 4.0 mph for 60 seconds.

Step 3. Slow down and stroll at 3.0 mph for 75 seconds.

Step 4. Repeat Steps 2 and 3 five more times.

Step 5. Finish with five minutes of walking at a comfortable pace to cool down.

And this is what a more advanced interval program would consist of:

Step 1. Warm up: Five minutes of jogging or cycling at the lowest possible percentage of your all-out effort.

Step 2. Run or cycle for 60 seconds at about 80%-90% of your all-out effort. As Dr. Gibala said, it should cause your leg muscles to fatigue in about one minute. (Basically, the speed you’d run or cycle at to save your life equals 100% of your all-out effort. From there, adjust how fast and hard you work so your output reflects the recommended percentage.)

Step 3. Slow down to 30% of your all-out effort for 75 seconds. (Make sure you slow down to this very light pace.)

Step 4. Repeat Steps 2 and 3 five more times.

Step 5. Finish with five minutes at 30% of your all-out effort to cool down.

As you become more experienced, you can increase the intensity of the interval. You can also use different modes of exercise to do intervals. If you like to train outdoors, you can do hill sprints or run in waist-deep water. And if you are resigned to a commercial gym, you can choose between the treadmill, crosstrainer, stationary bike, and even the rowing machine. It all comes down to having the ability to increase the workload for a short amount of time and then back off.

[Ed. Note: Craig Ballantyne trains athletes and executives in Toronto, and writes for Men’s Fitness magazine and Sylvester Stallone’s new magazine Sly. His trademarked Turbulence Training workouts and his comprehensive workout manuals (including The Executive Lifestyle Manual) are featured on his website www.TurbulenceTraining.com.]

Craig Ballantyne

Craig Ballantyne is the author of The Perfect Day Formula: How to Own the Day and Control Your Life. Craig has been a contributor to Men’s Health magazine for over 17 years. Today he teaches his gift high-performing entrepreneurs how to squeeze more out of their days, increase their income, and make more quality time for their families in his Perfect Life Workshop and Work-Life Mastery programs. Craig used his own advice to overcome crippling anxiety attacks in 2006, and he’ll teach you his 5 Pillars of Success so you can increase your income, decrease your work time, and live the life of your dreams. Learn more about Craig at craigballantyne.com