The term VO2max refers to the maximal rate of oxygen consumption of the whole body. The human body consumes oxygen all the time (VO2), and the rate of consumption tops out when we are at our maximal work rate. Understanding of VO2max is critical to certain types of exercise training and performance, specifically aerobic exercise in which higher performance is generally directly related to a higher VO2max.
Measuring VO2max directly and accurately requires metabolic measurement equipment that measures the volume of air a person breathes as well as the fraction of oxygen inspired and expired with each breath. Typically this involves performing some graded exercise (gradually increasing intensity) over approximately 8 - 12 minutes until maximal exertion is reached, while breathing through some sort of mask. The most common place to get a direct measure of VO2max is at a university kinesiology department, some of which will offer a fee for service test. The cost is often $150 - $200 per test. Most aerobic athletes who are competing at university level or higher will likely have their VO2max tested on numerous occasions. Other professional athletes will also get tested on a regular basis (for example, most National Hockey League teams include a VO2max test in their annual battery of tests at fall training camp). But many recreational athletes will never have the opportunity to be tested in that way. Depending on your interest level in sports, it may be worth having such a test conducted at some point, but there are a few things you'll want to note before and after the test to help future estimates of fitness without having to pay for another test. (See below).
There are several ways to estimate VO2max without directly measuring it. None are perfectly accurate and all have some built in errors and assumptions that result from individual differences between people. The American College of Sports Medicine (ACSM) provides a prediction equation for oxygen uptake (VO2) based on running or walking speed. The equations are:
running VO2 = (0.2 x speed) + [(0.9 x grade) x speed] + 3.5
walking VO2 = (0.1 x speed) + [(1.8 x grade) x speed] + 3.5
speed is expressed in metres per minute (e.g. 10 mph = 268 m/min) and grade is expressed as a percentage (e.g. 2% on the treadmill = 0.02)
As an example, if the treadmill running speed is 8.0 mph (214.4 m/min) and the grade is 1% (0.01), then the running VO2 = 48.3 ml/kg/min, which means that, on average, each kilogram of body weight is consuming 48.3 ml of oxygen every minute.
Since measurement of VO2max requires that the exercise intensity is sustainable (i.e. not a short sprint that lasts only a few seconds), you can not simply find the fastest speed you can run on a treadmill and then assume that is your VO2max. Your body can supplement the energy supplied by aerobic systems anaerobically (without the presence of oxygen) for short periods. Therefore, for short bursts you are capable of running at speeds higher than the speed that corresponds to your VO2max. In theory, if you knew what speed corresponds to your VO2max, then you could use the equation above to estimate your VO2max. One way of estimating this speed is to find the speed that you can run at for 5 - 6 minutes and no longer. Most people with some degree of exercise training can sustain their VO2max intensity for this time period, but are completely exhausted at the end of it. So, if you are able to run at 10mph for 5 - 6 minutes but no longer then it is a good bet you are running at or close to your VO2max at 10mph. Simply taking that speed and plugging it into the ACSM equation will estimate your VO2max. It is just an estimate because, like all such equations, it is based on averages for a large population and there is some variation between people.
Of course, getting your VO2max measured directly once in a while is not a bad idea if you are serious about performance. But, before (or within a few days following) the test, also run through the calculation above. Find your estimated VO2max from the running speed you can sustain for 5 - 6 minutes as above. That way, when you also have the direct measure you'll have an idea how accurate the prediction equation is for you. If your calculated VO2max is 57 ml/kg/min and the direct measure is only 53 ml/kg/min, then in future estimations you'll know your are over-estimating by about 7.5% and can adjust accordingly. It is also worth doing a VO2max test at a time in your training when you are familiar with several times for various performances (e.g. 1 mile run time, 10km run time, half marathon, etc.). In that way, you'll know exactly how your performance is at a given VO2max. In future, you'll be able to use these performance times to estimate whether your VO2max is above of below where it was previously when measured directly. (Though performance and VO2max are not perfectly correlated due to a number of other performance factors, they do have quite a strong relationship).
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