Running Intensity and Weight Loss

By Rick Morris

Running and weight loss are concepts that go together like peanut butter and jelly or cookies and milk. Running has almost always been associated with weight and fat loss. Many dedicated runners first started running in order to lose weight and gain health and fitness. Even elite runners will make some increases in their training levels in order to lose a pound or two for an important upcoming race. All athletes, in all sports, use running and a method for weight control and conditioning. But what about running intensity.

Running burns more calories, and as a result, more fat, than most any other form of cardiovascular exercise. The only other form of exercise that equals the calorie burn of running is cross-country skiing.

Running Intensity and VO2 max

In the past several years, there have been many fitness “professionals”, that are insisting that the best way to burn body fat is to exercise at a low level of intensity. They also say that walking is a better mode of exercise than running, if fat loss is your goal. They tell you to keep your exercise running intensity in “the zone” to maximize fat loss. The recommended “zone” is at around 50% to 65% of your maximum heart rate or about 28% to 50% of your VO2max. Pace wise, this is about 2 minutes per mile slower than your marathon pace. On the Borg Scale of Perceived Exertion this would be an easy workout.

The reasoning behind these “experts” claims is that a higher percentage of fat is burned when you are working at lower intensities. When you are working at 50% of your maximal heart rate (MHR), approximately 90% of the calories burned are coming from fat. When you increase your intensity to 75% of your MHR, the percentage drops to around 60% of calories burned coming from fat stores. Taking this information at face value, their recommendations appear valid. However, looking deeper into the numbers we find that working at the higher rate of intensity burns more total fat calories. A 30 minute workout at the lower intensity of 50% of MHR burns around 250 calories. Since 90% of those calories come from fat, there were 225 fat calories burned. Compare those numbers with the more intense level of 75% of MHR. At this intensity, about 447 total calories are burned. Sixty percent of those calories come from fat, giving 268 fat calories burned.

These numbers appear to be conservative. Studies have shown that individuals that work out at higher intensity levels have lower body fat percentages than people who exercise at lower levels of intensity. A recent study went as far as to say that higher intensity levels will result in 9 times the fat loss of a lower intensity workout.

There is a limit to the running intensity level you should use. If you go much harder than 85% of your MHR, the fat burning mechanisms in your body becomes less and less efficient. Levels that are from 75% to 85% are good levels to work toward.