Lab based Exercise Scientists and Physiologists have long used VO2 as the gold measure of ‘fitness’. Should we alter this standard to measure the ABILITY to complete physical tasks. VO2 measures the POTENTIAL to complete physical tasks.
VO2 compares the amount of oxygen expired by the body to the amount of oxygen present in the atmosphere. Atmospheric air is composed of an average of 20.93% oxygen, and by comparing this to the percentage of oxygen exhaled, we can extrapolate the oxygen consumption by the body, or VO2. Oxygen consumption can be further broken down into the ‘Fick’ Equation:
Oxygen Consumption = Cardiac Output x a–VO2 Difference
The difference in oxygen is caused by diffusion of the gas from the alveoli in the lungs to the capillary beds. The oxygen is then used to produce adenosine triphosphate during the process of cellular respiration. A by-product of this chemical reaction is carbon dioxide. If simple carbohydrates are the only source of fuel, the CO2 output will be equal to the O2 input. As this is rarely the case, the difference between the concentrations of these gases can provide an accurate indication of the proportions of carbohydrates, lipids and proteins used as fuel (the respiratory exchange ratio).
Thus, resting VO2 provides an effective measure of the amount and type of fuel being burned by the body at rest. As the resting VO2 is measured in a relaxed state, it does not provide an indication of energy required for activity, only the energy required to sustain normal maintenance of the body and includes the energy required to keep the heart beating, sustain breathing, repair tissues and keep the brain and nerves functioning (Lafferty et. al.). As oxygen is needed to release energy from food (one litre of oxygen releases ≈ 4.72 kilocalories – found using the Weir equation), VO2 also provides an accurate estimate of the Basal Metabolic Rate of the body.
It is vital to measure VO2 and thus BMR in the fields of medicine and nutrition. Daily energy requirements can be determined by adding the resting metabolic rate, dietary induced thermogenesis and energy demands of activity; the resulting value can be used to determine caloric intake and exercise levels required to maintain, increase or lose weight. An abnormally high basal metabolic rate (increased resting VO2 ) can indicate high levels of thyroid hormones in the blood (Hyperthyroidism), providing a medical explanation for rapid weight loss, while a low BMR can indicate low levels of thyroid hormones (Hypothyroidism), suggesting a reason for obesity.
BMR can also be used to asses body composition, as muscles are metabolically active, as opposed to fat which is not. At a more basic level, VO2 can provide an accurate measure of cardiopulmonary fitness. By taking weight into account, it is possible to correlate fitness levels regardless of the size of the subject. VO2 can also be used as a base to determine levels of intensity in exercise. A metabolic equivalent (MET) is a multiple of the resting metabolic rate which allows us to extrapolate how many times above the RMR a subject is exercising.
Ok, so that’s VO2 101 – a general overview of the ‘be all and end all’ of lab based Exercise Science. Does it have a place? Yes. In science we need to measure, and to measure we need to have a value. VO2 is this value. But is there a better way for us non labcoat wearing athletes (I use that term to describe anyone chasing improved health through exercise)? I think, ‘yes’. We can follow the same scientific principles as the Boffins. If we can meaure our exercise (whether it be in time, rounds completed, weight lifted or other) and we can replicate our exercise, then we can make judgements as to improvements. If you’re not measuring your exercise performance, you have no evidence that all the hard work you are doing is working. Apply a stimulus to your body (exercise), measure the outcome, repeat the process. If you’ve improved, keep going. If not, make a change.
