Most fitness books and magazines will tell you that the way to shed fat is to increase the
time and distance that you exercise. While endurance exercise does burn a lot of calories,
it is not the best way to decrease body fat.
During moderate-intensity exercise, the body burns fat for energy. And by engaging in
that type of activity over and over, you are effectively telling your body that you need
that fat. So, to prepare for the next time it is called on to repeat the activity, your body
will store more fat.
Conversely, when you engage in short bursts of high-intensity exercise, your body uses
glycogen stored in the muscle tissues for energy. Over time, this conditions your body to
store energy in the muscles - rather than as fat. Exercising this way will also cause you to
burn more fat during your recovery period, as the glycogen in the muscles is restored.
Consider this study performed by the University of Quebec. One group of exercisers
cycled for 45 minutes without stopping. Another group exercised for short bursts lasting
from 15 seconds to over a minute, with rests in between. The long-duration exercisers
burned more calories, but the short-duration exercisers lost more fat. In fact, nine times
more fat for every calorie burned.
This is why many endurance athletes have body fat percentages ranging from 10% to
20%, while sprinters have a well-muscled physique and usually carry only 4% to 8%
If you want to increase the health and strength of your heart, you don't need to spend
hours on a treadmill or run for miles and miles. In fact, doing that can be
Endurance exercise actually makes the heart, lungs, and muscles smaller, so they can
perform longer with less energy. But what you gain in efficiency, you lose in reserve
capacity. In other words, while you might be able to handle an hour-long jog, you
compromise your ability to produce bursts of energy. In your later years, it is this reserve
capacity that provides protection from heart attacks.
So if you want to improve the health and strength of your heart, focus on short intervals
of intense exercise punctuated by brief periods of recovery.