Have you ever talked to someone who was all smiles because they’d burned “X” number of calories doing a workout? Unfortunately, if they worked out on a piece of exercise equipment at the gym like an elliptical machine or exercise bike, they probably burned fewer calories than what the readout said. Calorie counts on exercise machines aren’t always accurate.
Despite the many health benefits of exercise, most people work out to burn calories and to improve body composition. Most studies show exercise works best in combination with dietary changes for significant weight loss. Exercise is essential for weight loss maintenance and for improving body composition. Plus, it’s important for your health!
What determines how many calories you burn during a workout? In addition, is the number of calories you burn during a workout really that important?
Is There an Accurate Way to Measure Calories Expended During Exercise?
You burn a certain number of calories at rest just to maintain normal body functions but during exercise calorie expenditure increases. Each time your muscles contract, you need ATP to fuel those contractions. Your body has to burn more calories to supply muscle cells with ATP. Your heart and respiratory muscles also work harder during a workout. This further increases the need for ATP and calorie expenditure.
In a research setting, you can measure calories burned through direct calorimetry. This technique measures the amount of heat your body releases during exercise. The amount of heat you release is a measure of how many calories you’re burning. Another less cumbersome way to measure calories expended during exercise is indirect calorimetry. During exercise, you take in more oxygen and release more carbon dioxide. Indirect calorimetry measures oxygen consumption and carbon dioxide release as an indirect marker for how many calories you’re expending.
Indirect calorimetry can also be used to measure resting energy expenditure (resting metabolic rate) and excess post-exercise oxygen consumption, the number of calories your body burns during the recovery phase of a workout, the so-called afterburn. Indirect calorimetry isn’t something you can do every time you work out. You have to have special equipment and wear a mask over your face during exercise to collect oxygen and carbon dioxide. Plus, indirect calorimetry is only accurate during steady-state exercise.
Another way to get a rough idea of calorie expenditure during exercise is to track your heart rate. Your heart rate increases as oxygen consumption goes up and oxygen consumption correlates with energy expenditure. This method isn’t extremely accurate since other factors like what you’ve eaten, how hydrated you are, body temperature, the temperature of the room you’re exercising in, the type of exercise you’re doing and even the position of your body can affect your heart rate during exercise.
Plus, when you do upper body exercises or static exercise, like isometrics, your heart rate rises more than when you do dynamic lower-body exercises. If you rely on heart rate as a measure of calorie expenditure with upper body or static exercises, you’ll get a falsely high heart rate reading. This reading won’t necessarily accurately reflect oxygen consumption or how many calories you’re burning.
Factors That Influence How Many Calories You Burn During a Workout
The two most obvious factors that affect how many calories you burn during an exercise session are intensity and duration. As exercise intensity increases, so does oxygen consumption and requirements for energy. Not surprisingly, the longer you work out, the more calories you burn. Sounds pretty straightforward, doesn’t it?
Body weight is another factor that affects calorie burn. A person who weighs 150 pounds burns more calories than a 100-pound person when they do any kind of weight-bearing exercise. In fact, the calories you burn simply walking around is directly related to your body mass. This partially explains why weight loss plateaus are so common. As you lose weight, you burn fewer calories when you exercise because your body has less body mass to move around. You’re burning fewer calories when you work out and with daily activities after losing weight and have to adjust your diet appropriately or increase the intensity of the exercise you do to avoid regaining the weight.
Another factor that affects how many calories you burn is how efficient your body is at doing a certain type of exercise. Do the same workout long enough and your body becomes more efficient at doing it. As a result, you don’t have to work as hard or expend as many calories. Your heart rate is lower, your movements are smoother and more coordinated so you don’t expend as many calories. Of course, there’s a simple solution – increase the intensity or try something new that your body is less efficient at doing. When you’re a highly conditioned athlete, you burn fewer calories during a workout.
Why You Shouldn’t Obsess over the Number of Calories You’re Burning
If you’re doing steady-state exercise, unless you work out for a long period of time, the calories you burn during a workout is pretty modest. It’s easy to “undo” it by eating a post-workout cookie. Rather than obsessing over the calories, you’re burning DURING a workout, increase the intensity of your exercise so you create a hormonal environment that boosts fat burning even after you’ve finished. A few sessions of HiiT training a week will help you do that. HiiT training creates an “after-burn” effect that keeps your body burning calories at a higher rate even after you finish. Steady-state exercise burns more calories only during the time you’re doing it, while HiiT workouts boost calorie expenditure during and afterward.
Heavy resistance training also activates fat-burning hormones that prime your metabolism. Plus, resistance training builds more metabolically-active lean body mass. It’s an investment in your metabolism. A study published in the International Journal of Sport Nutrition and Exercise Metabolism showed high-intensity resistance training also creates an after-burn effect that elevates your metabolism after a workout. That means more calories burned! Focus on compound exercises and exercises that use large muscle groups like weighted squats to maximize the after-burn.
The Bottom Line?
We’ve looked at a number of ways to measure calories burned during a workout but the most accurate methods aren’t very practical. A number of factors, as mentioned, can also affect calorie expenditure during a workout. Rather than focus so much on how many calories you’re burning during your workout, do more HiiT training and high-intensity resistance training to jack up the calorie burn even after you finish. Just as importantly, don’t justify eating something decadent just because you burned “X” number of calories.
References:
“Making Sense of Calorie-Burning Claims” Robert Robergs, Ph.D. and Len Kravitz, Ph.D
International Journal of Sport Nutrition and Exercise Metabolism, 10 (1), 71-81. (2000)
Medicine and Science in Sports and Exercise, 2002 Apr;34(4):715-22.
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