By Michelle Colvin, Spinning® Master Instructor | United Kingdom
VO2 sounds complicated but it isn’t. ‘V’ stands for volume and ‘O2’ stands for oxygen. VO2 is the volume or amount of oxygen your body consumes. The fitter you are, the more oxygen your body burns and the higher the score.
Peak VO2 is the measure of millilitres of oxygen consumed at maximal effort divided by a person’s weight in kilos per minute. VO2 max is an effective measure of fitness and your body’s maximum potential to perform work. It is impacted by (amongst other things) hereditary factors, age and health status.
Just like a car engine, your body needs oxygen to mix with fuel to produce energy. Your lungs (engine) 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, which causes you to breathe even harder. This point is typically referred to as your lactate or ventilatory threshold.
Measuring VO2 Variables: A Metabolic Assessment Profile
A metabolic assessment analyses 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 calorie intake needs for a weight loss programme.
An exercise metabolic assessment measures the VO2 and VCO2, blood lactate is measured 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 (VO2max), Aerobic Threshold (AeT), Lactate Threshold (LT) and Anaerobic Threshold (AT) are determined and these are used to develop a training programme. Target heart rates are scientifically determined by your metabolic assessment profile during exercise and can be incorporated into a fitness or weight loss-training programme.
What is determined from taking a metabolic Assessment is where your Lactate Threshold occurred in relation to your Heart Rate and as a percentage of your VO2 max. Typically, a Lactate Threshold of 65% or more of VO2 max represents above-average fitness while below 40% is considered deconditioned. Your Lactate Threshold also determines the type of recreational activities or sports in which you can comfortably participate at your current fitness level.
Metabolic assessments are useful because an exercise programme can be based on your unique response to exercise. An Exercise Professional or your Personal Trainer can use key elements from your exercise assessment to create an individualized plan to help you achieve your fitness goals. To further your training, your can wear a metabolic monitor or training device during exercise that to ensure you train at the proper intensity to maximize the effectiveness of your workouts.