VO2 max

VO2 max (also maximal oxygen consumption, maximal oxygen uptake, peak oxygen uptake or maximal aerobic capacity) is the maximum capacity of an individual's body to transport and use oxygen during incremental exercise, which reflects the physical fitness of the individual. The name is derived from V - volume, O2 - oxygen, max - maximum.

VO2 max is expressed either as an absolute rate in litres of oxygen per minute (l/min) or as a relative rate in millilitres of oxygen per kilogram of bodyweight per minute (ml/kg/min). The latter expression is often used to compare the performance of endurance sports athletes.

Measuring VO2 max
Accurately measuring VO2 max involves a physical effort sufficient in duration and intensity to fully tax the aerobic energy system. In general clinical and athletic testing, this usually involves a graded exercise test (either on a treadmill or on a cycle ergometer) in which exercise intensity is progressively increased while measuring ventilation and oxygen and carbon dioxide concentration of the inhaled and exhaled air. VO2 max is reached when oxygen consumption remains at steady state despite an increase in workload.

Fick equation
VO2 max is properly defined by the Fick equation:


 * $$\mathrm{VO_2\; max} = Q(\mathrm{CaO_2} - \mathrm{CvO_2})$$, when these values are obtained during an exertion at a maximal effort.


 * where Q is the cardiac output of the heart, CaO2 is the arterial oxygen content, and CvO2 is the venous oxygen content.


 * (CaO2 – CvO2) is also known as the arteriovenous oxygen difference.

Estimation of VO2 max
Tests measuring VO2 max can be dangerous in individuals who are not considered normal healthy subjects, as any problems with the respiratory and cardiovascular systems will be greatly exacerbated in clinically ill patients. Thus, many protocols for estimating VO2 max have been developed for those for whom a traditional VO2 max test would be too risky. These generally are similar to a VO2 max test, but do not reach the maximum of the respiratory and cardiovascular systems and are called sub-maximal tests.

Uth—Sørensen—Overgaard—Pedersen estimation
Another estimate of VO2 max, based on maximum and resting heart rates, was created by a group of researchers from Denmark. It is given by:
 * $$\mathrm{VO_2\; max} = {15{  \mbox{HR}_{max} \over \mbox{HR}_{rest} }}$$

This equation uses maximum heart rate (HRmax) and resting heart rate (HRrest) to estimate VO2 max in ml/min/kg.

Cooper test
Kenneth H. Cooper conducted a study for the United States Air Force in the late 1960s. One of the results of this was the Cooper test in which the distance covered running in 12 minutes is measured. Based on the measured distance, an estimate of VO2 max (in ml/min/kg) is:


 * $$\mathrm{VO_2\; max} = {d_{12} - 505 \over 45}$$

where d12 is distance (in metres) covered in 12 minutes. There are several other reliable tests and VO2 max calculators to estimate VO2 max, most notably the multi-stage fitness test (or bleep test), based on the research paper by Leger and Lambert, "A Maximal Multi-Stage 20m Shuttle Run Test to predict VO2 Max".

VO2 max levels
“Maximal oxygen uptake (VO2max) is widely accepted as the single best measure of cardiovascular fitness and maximal aerobic power. Absolute values of VO2max are typically 40-60% higher in men than in women.”

The average untrained healthy male will have a VO2 max of approximately 35-40 ml/kg/min. The average untrained healthy female will score a VO2 max of approximately 27-31 ml/kg/min. These scores can improve with training and decrease with age, though the degree of trainability also varies very widely: conditioning may double VO2max in some individuals, and will marginally improve it in others.

In sports where endurance is an important component in performance, such as cycling, rowing, cross-country skiing, swimming and running, world class athletes typically have high VO2 maxima. Elite male runners can generate up to 85 ml/kg/min, and female elite runners can generate about 77 ml/kg/min. Five time Tour de France winner Miguel Indurain is reported to have had a VO2 max of 88.0 at his peak, while cross-country skier Bjørn Dæhlie measured at 96 ml/kg/min. Dæhlie's result was achieved out of season, and physiologist Erlend Hem who was responsible for the testing stated that he would not discount the possibility of the skier passing 100 ml/kg/min at his absolute peak. Norwegian cyclist Oskar Svendsen is thought to have recorded the highest VO2 max of 97.5 ml/kg/min, a "sensational" value in itself, made more remarkable by his young age (18 years old at the time). World class rowers are physically very large endurance athletes and typically do not score as high on a per weight basis, but often score exceptionally high in absolute terms. Male rowers typically score VO2 maxima over 6 litres/minute, and some exceptional individuals have exceeded 8 l/min.

To put this into perspective, thoroughbred horses have a VO2 max of around 180 ml/kg/min. Siberian dogs running in the Iditarod Trail Sled Dog Race have VO2 values as high as 240 ml/kg/min.

Factors affecting VO2 max
The factors affecting VO2 are often divided into supply and demand factors. Supply is the transport of oxygen from the lungs to the mitochondria (including lung diffusion, stroke volume, blood volume, and capillary density of the skeletal muscle) while demand is the rate at which the mitochondria can reduce oxygen in the process of oxidative phosphorylation. Of these, the supply factor is often considered to be the limiting one. However, it has also been argued that while trained subjects probably are supply limited, untrained subjects can indeed have a demand limitation.

Tim Noakes, a professor of exercise and sports science at the University of Cape Town, describes a number of variables that may affect VO2 max: age, gender, fitness and training, changes in altitude, and action of the ventilatory muscles. Noakes also asserts that VO2 max is a relatively poor predictor of performance in runners due to variations in running economy and fatigue resistance during prolonged exercise.

Cardiac output, pulmonary diffusion capacity, oxygen carrying capacity, and other peripheral limitations like muscle diffusion capacity, mitochondrial enzymes, and capillary density are all examples of VO2 max determinants. The body works as a system. If one of these factor is sub-par, then the whole system loses its normal capacity to function properly.

In theory, the drug Erythropoietin (EPO) can boost VO2 by a significant amount. This makes it attractive to dopers in endurance sports like professional cycling. By 1998 it had become widespread in cycling and led to the Festina affair as well as being mentioned ubiquitously in the USADA 2012 report on the US Postal team. Greg LeMond has suggested establishing a baseline for riders' VO2 (and other attributes) to detect abnormal performance increases.