What is interval training?

Interval training involves alternating between high and low intensities for specific lengths of time during a workout. The general format of an interval workout is determined by the exercise-to-rest ratios or work-to-recovery ratios. Because the high-intensity (work) portions of the intervals are so intense, they can be performed for only a short period and need to be followed by a lower-intensity (recovery) phase before the next high-intensity phase begins.

Beginners should start their high-intensity intervals at 10-15 seconds and can progress up to 30-90-second intervals, but shouldn't exceed more than 120 seconds per interval. If you can go that long, you probably aren't exercising hard enough! Instead, boost the value of your exercise investment by moving quickly and intensely during the workout. One benefit of interval training is that you'll cut your exercise time almost in half - but it will seem like you're doing even more work because of the speed and intensity of the workout.

Check out the research

We used to think that exercising at a low intensity for a long period would burn the most fat; most women probably still believe that 45-50 minutes of stair-stepping at a moderate pace is ideal. Time to step into the 21st century, ladies, and read the research on the wall. Many studies indicate that as exercise intensity increases, so does total energy expenditure.

And get this: With higher-intensity exercise comes a stimulation of fat stores. Other studies show that while an endurance-training program (which requires a longer duration of work) may burn more calories, a high-intensity interval training program burns more fat. In fact, the interval-training group in these studies lost fat at a rate nine times that of the endurance group! The interval group also gained lean muscle while losing fat in less time per exercise session (30 minutes compared to 45) and in fewer weeks (15 compared to 20 weeks).

With the increase in lean muscle and the extra postexercise oxygen consumption needed from the additional energy expenditure, your metabolic rate will remain elevated after exercise. Think of it as quality vs. quantity: You can spend 45 minutes on the stair-stepper at Level 4 and burn some calories at the gym, or you can invest 20 minutes doing stair intervals at Levels 4 and 7 and burn some calories during the activity, then keep burning calories at a higher rate the rest of the day!

But the real goal in exercising to lose bodyfat should concentrate on increasing your metabolic rate, not just the number of calories burned, right? So why do we consider all the long, slow cardio exercise we do to be fat-burning, when it's actually just calorie-burning? As Conrad Earnest, PhD, CSCS, exercise physiologist at the Cooper Institute in Dallas, explains: "Long, slow distance exercise is often recommended because it's simple and safe, and the proportion of fat used to fuel the exercise is greater than during high-intensity exercise. But don't let that fool you. Assuming all safety-related issues as a given, it isn't the proportion of fat burned that's important for weight loss, it's the quantity of fat."

Unfortunately, long, slow endurance exercise can also cost you muscle. Why work hard lifting weights to build muscle just to eat it up during a long, slow cardiovascular session? And when you lose muscle, you decrease your body's resting metabolic rate, meaning that you must decrease your calories even more to maintain or lose weight. That's what's known as a no-win situation!

Training Wisely

The key to changing your cardiovascular-endurance workout into an interval session relies on the intensity of the work and the work-to-recovery ratios (WRR). We provide the basics on a couple of programs here, but it's always a good idea to consult a physician before beginning any new exercise routine, especially one as intense as interval training.

Earnest notes that using any interval training program more than three days a week will likely lead to overtraining and injury. To avoid this, remember the motto quality, not quantity, which also applies to the length of each interval session. A five-minute warm-up, five-minute cool-down and 20-30 minutes of intervals is really all you need to burn fat and increase your level of fitness.

The fun of interval training comes in designing your program. With no hard and fast rules, you can vary the WRRs to accommodate your current level of fitness as well as your own personal preferences. You can easily incorporate variety and eliminate boredom when you speed up and slow down at different time intervals. For instance, you can choose a WRR of 1:1 so you exercise at a high intensity for a certain amount of seconds (let's say 30) and recover for the same amount of time. If the WRR you choose is 1:2, you'd exercise intensely for 30 seconds and recover for 60 seconds.

The longer your work interval is and/or the more intensely you perform it, the longer your recovery needs to be. So, at first, if your work interval is up to two minutes, you may need a recovery interval of 10 minutes. That's a WRR of 1:5. Decrease your recovery intervals when your fitness level increases. It helps to have a good aerobics base before you begin interval training, but resistance training may actually be even more valuable to prepare the muscles for the high power production necessary.

Let's get interval

Ready for what may be the toughest, most efficient workout you've ever had? You'll not only decrease your time in the gym but get even better results from your fat-burning efforts. In terms of fat loss, slower isn't better. Kick it up a notch and get intense with interval training. As Earnest says, "All you have to lose is a little extra fat!"     

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