VO₂ Max is a measure of how fit an athlete is: it expresses the volume of oxygen a body consumes per minute.

Athletic performance is directly related to the amount of oxygen supplied to the muscles. The supply of oxygen is dictated by how often the heart beats, the volume of blood transported by every beat and the amount of oxygen in that blood. It is also dependent on how well the tissue or muscle extracts the oxygen. So if we could find the volume of blood pumped in one minute and the difference between the amount of oxygen in arterial and venous blood, we would have all the data we need. The stroke volume is usually measured in millilitres per beat. The cardiac output is the product of stroke volume and heart rate and is measured in millilitres per minute. Multiply this by the difference in oxygen concentration and we have the litres of O₂¹ processed per minute. If we make these measurements when the athlete is working at his or her maximum heart rate, we have VO₂ Max.

A straight comparison of the absolute amount of oxygen that the bodies of two different athletes can process is not quite fair. A heavy-weight athlete with the same values would not perform as well as a lighter athlete. For most sports, including running, VO₂ Max is expressed as VO₂/Kg - millilitres of O₂ per minute per kilogram of body weight. Cyclists tend to be measured strictly in terms of litres of O₂ per minute because body weight is less important in that sport.

Direct Measurement

To measure VO₂ Max directly an athlete has to be wired to a computer and breathe into an apparatus that analyses exhaled air while he runs on a tread mill. The equipment is expensive and the test is not practical for most people. Strictly speaking, in this case it is VO₂ peak that is measured anyway - it becomes too painful for anyone but the highly motivated to reach the maximum.

Indirect Measurement

If we measure a group of athletes directly and take them to the maximum and then have them perform some simpler, submaximal test, we can find an equation to extrapolate the indirect test result to a predicted VO₂ Max value. There are some problems with this - the test is not always accurate and maximum heart rate factors into the equation. Because the subject isn't taken to the limit, a theoretical maximum heart rate number must be used. A common estimate is 220 - age. This, the Karvonen formula, is said to be accurate for 75% of the population with a margin of error of 10-15 beats per minute. However, if you are interested in a rough measurement to use as a base against which to measure your progress, then indirect measurement is fine.

Improving VO₂ Max

You probably just realised that you can improve your VO₂/Kg simply by losing weight, assuming you lose fat and not muscle. Women are at a slight disadvantage because they have a higher percentage of essential body fat.

There is not much that can be done to increase max heart rate - in fact it decreases with age. We can increase the cardiac output by making the heart larger and stronger, which we do over the years through prolonged endurance training. A trained athlete's resting heart rate is lower because it pumps more blood per beat than an untrained person's does.

The last parameter in the equation is the body's ability to extract more oxygen out of the arterial blood, which is increased mainly as a result of long, slow endurance runs. The aerobic capacity of Type I fibres is improved only after 1.5 hour's exercise.

Real Numbers

The chart shows actual figures from this Researcher's test at the Science Centre in 1989. The subject's VO₂/Kg peaked at 63.2 ml/minute/kg after 13 minutes of progressively faster and steeper running on a treadmill. The subject weighed 72.1 kg at the time. This means the VO₂ MAX was 4.6 litres/min. The test listed a lot of other data, things like litres per breath and the VCO₂ (at STP) that are used during the calculation of VO₂. A MET is a metabolic equivalence unit. One MET is equal to 3.5 ml/kg/min and is the amount of oxygen the body uses at rest.

If you want to compare yourself with real mortals, here are tables from Ästrand, 1960. There's one for men and one for women. The tables list VO₂/Kg in ml/min/kg for a range of ages and levels of fitness.

Here, expressed as VO₂/Kg are some well-known athletes' statistics.

• Carlos Lopes - 85.1

• Grete Weitz - 73.5

• Matt Carpenter - 92

• Miguel Indurain - 88

• Greg LeMond - 92.5

• Ed Whitlock² - 52.8 (at 69 years)

Indirect VO₂/Kg Test

Here is one indirect test you can do yourself. It is the Rockport Fitness Walking Test (RFWT), named from the shoe company of the same name.

To perform the test, all you need is your weight and age and to walk one mile. Before the walk, warm up with some stretching. After the warm up, walk one mile as fast as possible and note the time it took you. Immediately after finishing the mile, take your pulse. The equation for estimating your VO₂/Kg follows:

• Weight is in pounds
• Age is in years
• Sex: male = 1, female = 0
• Time is expressed in minutes and 100ths
• Heart rate is in beats per minute, taken at the end of the walk

Notice how gender adds a constant 6.3 to the male score. It's interesting that the Ästrad tables differ by roughly this order of magnitude for the average, middle-aged man and woman.

Conclusion

A high VO₂ Max alone does not make a super athlete. On competition day, psychological factors are important. If it's a race, then pacing and tactics are also critical. Depending on the sport, mechanical efficiency and technique play a large role. If lactate tolerance is low, then a super VO₂ Max is all for naught - interval training can help here. But as a measure of the efficiency of the amazing heart/lung/muscle machine, V0₂ Max is the standard.