Your body derives most of its energy from a system that uses oxygen. For this reason, your energy requirements can be estimated from the amount of oxygen you consume. When you are sleeping, your body still requires some energy to maintain its internal environment. You consume oxygen as you sleep to fulfill this requirement.
Oxygen
Oxygen is a gas that makes up 20.9 percent of atmospheric air. When you inhale air into your lungs, oxygen moves into blood that transports it to your tissues. When blood flows through your tissues, oxygen is removed and consumed to produce energy. Any oxygen that is not consumed is moved back to your lungs and exhaled.
Oxygen Consumption
Metabolic rate is the sum of all energy-requiring processes in a living organism. This value can be estimated based upon the fact that all metabolic processes ultimately require the consumption of oxygen. Oxygen consumption is often measured using open-circuit spirometry. This computer-based technology measures the amount of oxygen in the air you exhale and calculates the difference between this value and the amount that is in the air you inhale. This reveals the oxygen you have consumed with each breath.
Resting Metabolic Rate
Your resting metabolic rate, or RMR, is the amount of energy you need to maintain your vital bodily functions in the waking state at rest. Measurements derived using open-circuit spirometry have shown that a person consumes 3.5 mL. of oxygen per kilogram of body mass each minute to satisfy his RMR. Metabolic equivalents, or METs, are multiples of the RMR that can be used to quantify any activity. For example, measurements have shown that jogging 6 miles per hour on flat terrain requires 10.2 METS. This means that you use 35.7 mL. of oxygen per kilogram of body mass each minute when you run at this speed.
Basal Metabolic Rate
Your basal metabolic rate, or BMR, is the oxygen you require at rest under very specific conditions. Unlike RMR, BMR is measured after 12 hours of fasting because metabolism is increased when you are digesting, absorbing and assimilating nutrients. Measurement of BMR also requires abstinence from physical activity prior to the test. Typically, a subject lies supine for 30 minutes in a room with a neutral temperature before having their BMR measured. BMR values usually fall only slightly below RMR values, so the two terms are often used interchangeably.
Sleep
Sleeping requires less energy than your RMR because of the decreased state of arousal compared to the waking state. Measurements have shown that the MET value for sleeping is 0.9, although this will vary, depending upon quality of sleep and also what took place prior. A MET value of 0.9 indicates that the average person consumes 3.15 mL. of oxygen per kilogram of body mass each minute while he is asleep. This means that a 175-lb. person consumes 120 L. of oxygen during eight hours of sleep.
References
- "Exercise Physiology: Nutrition, Energy, and Human Performance Seventh Edition"; W.D. McArdle, F.I. Katch and V.L. Katch; 2010
- Linking the American Time Use Survey (ATUS) and the Compendium of Physical Activities: Methods and Rationale
