Study Dispels Myth of Post-Workout Fat Burn

After an intense hour of sweating on the treadmill or pumping iron, most of us look forward to the extra post-exercise "afterburn" of fat cells that has been promised to us by fitness pundits. This 24-hour period of altered metabolism is supposed to help with our overall weight loss.

Unfortunately, a recent study found this to be a myth for moderate exercisers.

The new research clarifies a misunderstanding that exercisers can ignore their diet after a workout because their metabolism is in this super active state.

"It's not that exercise doesn't burn fat," said Edward Melanson, associate professor of medicine at the University of Colorado, "It's just that we replace the calories. People think they have a license to eat whatever they want, and our research shows that is definitely not the case. You can easily undo what you set out to do.”

The findings were detailed in the April edition of Exercise and Sport Sciences Review.

What does happen

Melanson and his team set out to measure whether people were able to burn more calories for the 24 hours after a workout compared to a day with no exercise. Their test groups, totaling 65 volunteers, included a mix of lean vs. obese and active vs. sedentary people.

On exercise days, they rode stationary bikes until they had burned 400 calories. Their pre and post exercise diet was controlled.

Throughout the groups, there was no difference in the amount of fat burned in the 24-hour period either with or without exercise.

Of course, during the exercise plenty of calories were being burned and that's the formula that Melanson would like us to remember.

"If you are using exercise to lose body weight or body fat, you have to consider how many calories you are expending and how many you are taking in," Melanson recently told WebMd. The daily energy balance or "calories in vs. calories out" is the most reliable equation for long-term weight loss.

While the current research focused on the moderate activity levels of most people, the researchers admitted they still need to examine the effect of higher intensity workouts and multiple consecutive days of exercise.

They are clear on their current message. "We suggest that it is time to put the myth that low intensity exercise promotes a greater fat burn to rest," Melanson writes. "Clearly, exercise intensity does not have an effect on daily fat balance, if intake is unchanged."

Type of workout

So, how about a weight resistance training program mixed in with cardio work?

Another fitness industry claim is that more muscle mass on your frame will raise your metabolism rate, even while sitting on the couch.

The same study, using the same test groups, found the post-exercise rate of calorie burn did not change on days of lifting versus no lifting. It is true that a pound of muscle burns seven to ten calories per day versus only two calories per day for a pound of fat. However, the average adult just doesn't put on enough lean muscle mass to make this difference significant.

While this research dispels one myth about exercise, there is still overwhelming evidence of the benefits of movement when combined with your eating habits. So, before eating that double cheeseburger and fries, you might want to do some math to figure out how many stairs you'll have to climb to break even.

• Exercise Won't Cure Obesity
• How Your Inner Athlete Makes You Smarter
• Video: Exercise in Your Genes

Dan Peterson writes about sports science at his site Sports Are 80 Percent Mental. His Science of Sports column appears weekly on LiveScience.