Edited by Kate Findley and proofread by Angela Shoemaker, Wondrium Daily
Even if you exercise on a regular basis, it’s important to know whether your exercise is paying off and you’re burning more calories than you’re consuming. Professor Ormsbee explains how to do the calculations.
What Is Caloric Cost?
What is the caloric cost of exercise, or the net energy consumed by an activity? If you want to manipulate your body composition, it is important to know the quality of your calories and how many calories you are eating and drinking and how many calories you are expending. Various types of exercises demand varying amounts of energy—walking versus running, for example—and these energy demands are measured scientifically through what we call metabolic testing.
Metabolic testing measures the amount of oxygen you take in during activity. The more strenuous or intense the activity is, the greater the oxygen consumption. On average, humans consume 3.5 ml of oxygen per kg of their body weight per minute at rest.
Today we have all kinds of technology that estimate calories burned, but, not long ago, the caloric cost of exercise was traditionally measured in what we call mets or metabolic equivalents. You may have seen the mets term on the exercise equipment in your home or at your local gym.
Measuring Exercise Intensity
Measuring exercise intensity is simply another way to assess or quantify the intensity level of your exercise. One metabolic equivalent is equal to the oxygen consumption of your body at rest—as mentioned, 3.5 ml/kg/min. When measuring mets, everything is compared to the cost of energy at rest.
So, the more strenuous the exercise, the higher the met value will be—that is, the higher the caloric expenditure will be in relation to being at rest. For example, running at 10 mph, or a 6:00 min/mile pace, equals 14.5 mets, and that means it requires 14.5 times more energy than resting.
Using mets as a measure of your exercise intensity might seem a bit odd and strange at first, but if you are trying to determine the number of calories you burn when you are exercising—in other words, your caloric cost of exercise—then a great estimate is to simply multiply the met value by your body weight in kg.
For example, if you are exercising at an intensity of 10 mets on a stationary cycle in your local gym and you weigh 80 kg or 176 lbs, then you are expending approximately 800 kcal per hour of exercise. For those of you who don’t use the metric system, all you have to do to figure out your weight in kg is to divide your weight in lbs by 2.2.
Choosing the Best Workout
You might be wondering how this applies to your daily life. How long does it take to burn off that bag of chips you just ate or the two extra cookies you ate after dinner last night? Do you have to walk for an hour or two hours? Let’s tackle these questions with a case study of our own.
As you probably already know, the type of exercise you participate in dictates how many calories you burn. Have you ever heard someone say that you burn more fat walking than you do running, so why run?
According to this theory, walking hits your fat burning zone. Because of the way the body’s three energy systems work—the creatine phosphate, the glycolytic, and the oxidative systems—it seems that a lower intensity activity should burn more fat.
Well, this is partially correct. A higher percentage of fat is burned from the total calories you use during low-intensity exercise. However, the tricky part rests with the actual number of calories burned from the exercise.
Even though during high-intensity exercise a lower percentage of fat is burned, the total number of calories burned is typically far greater than during low-intensity exercise. Thus, the absolute amount of fat burned is typically greater with high-intensity exercise.
For example, suppose you walk for an hour and burn 300 total calories and 50% of that is from fat, so you have burned 150 calories of fat. Now, suppose you run for an hour and burn 1,000 total calories.
Even if only 25% is from fat, you have now burned 250 calories of fat with the higher intensity exercise. Therefore, despite a lower percentage of fat burned when you run hard, you actually burn more fat because the caloric cost of this exercise was so much higher than the caloric cost of walking for an hour.
Michael Ormsbee is an Associate Professor in the Department of Nutrition, Food, and Exercise Sciences and Interim Director of the Institute of Sports Sciences and Medicine in the College of Human Sciences at Florida State University. He received his MS in Exercise Physiology from South Dakota State University and his PhD in Bioenergetics from East Carolina University.