WHY SHOULD I CARE WHAT MY RMR IS?
What is RMR? RMR stands for resting metabolic rate. Resting metabolic rate can simply be defined as the total amount of calories your body requires on a daily basis to perform normal physiological functions (i.e. digestion, breathing, or pumping blood throughout the body) and light activities (i.e. brushing your teeth, folding laundry, standing while cooking). RMR does not include exercise, however exercise and the type of exercise do in fact influence your overall RMR and total caloric intake. For example, if your RMR is 1,500 calories and you burn an extra 300 calories through exercise, then your maintenance caloric intake would be roughly 1,800 calories. The type of exercise can also influence your RMR. For example, people who weight train tend to have a higher RMR because increasing muscle mass will increase your RMR. Muscle tissue requires more energy and is more metabolically active than fat, meaning muscle tissue will burn more calories at rest than fat tissue!
How can I use RMR? Knowing your RMR is important because it goes hand in hand with your goals. For example, if you are trying to lose weight, RMR testing is a great way to create a more accurate nutrition plan. Rather than guessing or using prediction equations, knowing your actual RMR can help a nutritionist or coach write a more detailed plan based on your needs. Say you think your RMR is 1,300 calories and due to exercise you predict your maintenance caloric intake to be roughly 1,600 calories. After testing your RMR you find it's actually much higher, roughly 1,800 calories (making your maintenance intake ~2,100). Therefore, you have not been eating enough calories to adequately fuel your body and metabolism properly. Overtime, this can slow your metabolism (and lower your RMR) and negatively decline performance.
How to test RMR? RMR can be predicted using equations that take into consideration variables like height, weight, gender, body fat and lean muscle mass. However, the “gold standard” approach is indirect calorimetry. Indirect calorimetry is a method that measures the volume/concentration of oxygen and carbon dioxide via inspired and expired air. In a normal setting, a metabolic cart and a test administer are required to perform the test. The person being measured sits in a comfortable resting position with a tube in their mouth causing all respiration to flow into the metabolic cart to be analyzed. A test like this typically lasts ~10-30 minutes. Prior to the test, you are instructed to fast, avoid supplements and caffeine, and avoid exercise for roughly 12 hours beforehand (all of these factors can skew the results).
What influences RMR?
Age
Gender
Stature (Height and Weight)
Amount of Muscle Mass
Medications
Brain Activity
Disease State
Organ Functioning
Emotional Stress / Chronic Levels of Elevated Stress
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