Your body burns calories, even when you're not exercising. This is referred to as your resting metabolic rate, or metabolism, which is the calories burned sitting or sleeping — in other words, while you're at rest.
Calories Burned Sitting
Even when you're sitting still, your body is burning calories because of the metabolic processes going on inside, according to the American Council on Exercise (ACE). Therefore, your resting metabolic rate, also known as RMR or metabolism, is the calories your body is burning during this sedentary period. The Mayo Clinic notes that your individual metabolism is influenced by a number of factors, including your body size, the amount of muscle versus fat on your body, your sex and your age.
Although similar, RMR is different than your basal metabolic rate, or BMR. ACE explains that BMR is a restrictive measurement of the calories you're burning in a totally rested, post-absorptive state in a neutral environment. It's usually used in clinical settings.
It is possible to find out your specific RMR, but it's not simple. Indirect calorimetry uses the oxygen you breathe in and the carbon dioxide you breathe out to determine the amount and types of fuel you're burning, according to research published in November 2016 in the European Journal of Clinical Nutrition. Figuring this out requires a special device; however, in absence of that, you can calculate your estimated RMR with a little bit of simple math.
Calculating Your RMR
You can estimate the number of calories you burn each day with an equation that takes your weight, height, gender and age into account. It's known as the Mifflin-St. Jeor Equation, according to the National Academy of Sports Medicine (NASM).
- For men: (10 x weight in kilograms) + (6.25 x height in centimeters) - (5 x age in years) + 5
- For women: (10 x weight in kilograms) + (6.25 x height in centimeters) - (5 x age) - 161
For example, a 45-year-old woman who weighs 154 pounds and is 5 feet, 5 inches tall would have an RMR of 1,343, which is the number of calories she should eat per day to maintain her weight. Keep in mind that this number is only an estimate, as NASM notes that lean body mass can significantly influence your RMR.
Increasing Your RMR
It's possible to increase your RMR, according to Harvard Health Publishing. Perhaps the best way to improve your RMR through exercise is by lifting weights and high-intensity interval training (HIIT).
Physical activity recommendations from the Dietary Guidelines of Americans, 2015-2020, advises adults to lift weights for all major muscle groups at least two days a week. A study published in October 2014 in the European Journal of Clinical Nutrition found that nine months of resistance training increased a person's RMR by approximately 5 percent, though it noted that there was varied results between individuals based on their body fat and hormone levels.
Additionally, high-intensity interval training — a workout consisting of short periods of intense effort at 80 percent to 95 percent of maximum heart rate, followed by a recovery period — has an effect on your metabolism, according to the American College of Sports Medicine. For about two hours after a HIIT workout, your body burns more calories than it did before the workout — even while you're sitting.
Read more: How to Build the Best HIIT Workout for You
- American Council on Exercise: "Resting Metabolic Rate: Best Way to Measure It—And Raise It, Too"
- National Academy of Sports Medicine: "Resting Metabolic Rate: How to Calculate and Improve Yours"
- European Journal of Clinical Nutrition: "Indirect Calorimetry: An Indispensable Tool to Understand and Predict Obesity"
- Harvard Health Publishing: "Exercise and Weight Loss: The Importance of Resting Energy Expenditure"
- European Journal of Clinical Nutrition: "Effect of Resistance Training on Resting Metabolic Rate and Its Estimation by a Dual-Energy X-Ray Absorptiometry Metabolic Map"
- Health.gov: "Dietary Guidelines for Americans, 2015-2020: Appendix 1. Physical Activity Guidelines for Americans"
- Mayo Clinic: "Metabolism and Weight Loss: How You Burn Calories"
- American College of Sports Medicine: "ACSM Information on...High-Intensity Interval Training"