An average adult consumes nearly a million calories a year. Despite this huge number, some healthy people are able to maintain a relatively stable body weight over years and decades without much conscious effort. When "calories in" equals "calories out," a state of energy balance is achieved and body weight remains constant.
Metabolism is the process of converting food to fuel for the body. Metabolic rate is the number of calories used to fuel the body. Therefore, your resting metabolism is the amount of energy your body uses at rest.
The Role of Oxygen, VO2
Just like an automobile engine, your body needs oxygen to mix with fuel to produce energy. Your lungs (carburator) and heart (fuel pump) deliver oxygen to the individual muscle cells and combine with fuels (fat, carbohydrates) for the production of energy. One of the by-products (exhaust) of this energy creation is carbon dioxide. You breathe in oxygen and you breathe out carbon dioxide.
At lower exercise intensities, your aerobic system uses fats and some carbohydrates as fuel along with a moderate amount of oxygen. Of these fuels, only carbohydrates have the capacity to be used as fuel without oxygen or anaerobically. As the intensity of your exercise increases and you reach the capacity of your aerobic system, to bring oxygen into your body and you shift progressively to your anaerobic system. Your anaerobic system primarily uses carbohydrates (in the form of blood sugar or stored glycogen) as a fuel source and produces an increased amount of carbon dioxide exhaled.
For example, if you are walking up a few flights of stairs, as you get to perhaps the third flight, you begin to switch from your aerobic system to your anaerobic system and will notice an increased demand for oxygen and you will breathe harder and more rapidly. If you continue to climb the next flight of stairs, you will notice a burning sensation (accumulation of lactic acid) in your leg muscles and as this lactic acid accumulates in the muscle, your body attempts to rid itself of this condition by buffering it with bicarbonate in the blood. This buffering process produces additional carbon dioxide in the blood that causes you to breathe even harder. This point is typically referred to as your anaerobic or ventilatory threshold.
A metabolic assessment analyzes the volume of oxygen consumed (VO2) and the volume of carbon dioxide produced (VCO2) in a controlled setting to determine the type of fuels your body is using, or your "metabolic profile". A Resting Metabolic Rate (RMR) assessment measures the amount of energy used at rest. The RMR is then adjusted by an activity factor to produce the amount of calories you burn in a typical day. Your RMR can be used to identify your caloric intake needs for a weight loss program (e.g. 2000 calories per day).
An exercise metabolic assessment measures the VO2 and VCO2 along with your heart rate during exercise with a gradual increase in intensity until you reach a point sufficient to collect the desired exercise "metabolic profile". Data such as heart rate, oxygen consumed (VO2 Max), and Anaerobic Threshold (AT) are determined and these are used to develop training program for you. Target heart rates are scientifically determined by your metabolic profile during exercise and can be incorporated into a fitness or weight-loss training program by your exercise professional.
Metabolic assessments are better than estimates because the program is based on your unique response to exercise. Your exercise professional will have more information from the assessments on how your body is working which leads to more effective nutritional planning and exercise programming.
Consult your physician before starting any exercise or nutrition program!
Everyone has a unique metabolism.....
just like they have different fingerprints and DNA.