How is VO2 Max Measured?
The direct measurement of VO2 max during a maximum exercise test provides the most accurate assessment of aerobic power. Measuring VO2 max requires some sophisticated laboratory equipment, including oxygen and carbon dioxide gas analyzers, an expiratory air flow probe, an air mixing chamber, a dehumidifier, a vacuum pump and a data acquisition system. Some computerized systems contain all of these things in one unit.
There are many testing variables that can affect the determination of VO2 max, including:
- the type of exercise (typically cycling or running)
- whether a treadmill test incorporates increases in grade and speed
- the environment in which the test is conducted (altitude, temperature, humidity)
- the specific measurement system used, the sampling interval for respiratory gases—the foreign open-ended nature of the test that requires individuals to continue running or cycling until they no longer can
- the duration of the test and its stages.
Although the classical definition of VO2 max is the maximum volume of oxygen that is consumed per minute, many laboratories collect air samples over a shorter time period (sometimes for each breath), and extrapolate to a minute's value. All of these differences make the comparison of VO2 max values obtained from different labs difficult.
Typically, the treadmill test starts at a slow speed (about the runner's normal easy running pace) and gets progressively harder with each stage, initially with increasing speed and then with increasing grade, until the runner is completely exhausted and can no longer keep pace with the treadmill. The runner runs while breathing through a snorkel-like mouthpiece that connects him or her to respiratory gas analyzers, and wearing a nose clip to prevent breathing through his or her nose. The whole test takes about 10 to 15 minutes.
VO2 max can be measured either in liters of oxygen per minute (L/min) or in milliliters of oxygen per kilogram of body weight per minute (ml/kg/min). In order to compare runners of different sizes, it is usually measured relative to body weight. The greater the amount of muscle mass used during the test, the higher the VO2 max.
More: Maximize Your VO2 Max
For example, running results in a 10 to 15 percent higher VO2 max than cycling (unless testing a trained cyclist). The VO2 max of elite male endurance athletes is over 70 ml/kg/min, while that of elite female endurance athletes is over 60 ml/kg/min. Men have a higher VO2 max than women because they have a greater cardiac output to send more blood and oxygen to the muscles, more hemoglobin in their blood to transport oxygen, and more muscle mass to consume oxygen. Even when the difference in muscle mass between men and women is accounted for and VO2 max is expressed relative to lean body mass, men still have a higher VO2 max than women. But there are plenty of female endurance athletes who have a higher VO2 max than most men.
The highest VO2 max ever recorded is that of Bjorn Daehlie, a cross-country skier from Norway who won eight gold and four silver medals in three Olympic Games from 1992 to 1998. His VO2 max when he was competing has been reported to be an astounding 93 to 95 ml/kg/min. The VO2 max of other cross-country skiers has also been tested to be in the 90s. Comparatively, Olympic 5,000-meter 4th place finisher Steve Prefontaine's VO2 max was 84; Olympic Marathon gold and silver medalist Frank Shorter's was 71; Olympic 1500-meter silver medalist and former world 1500-meter record holder Jim Ryun's was 81; and nine-time New York City Marathon champion Grete Waitz's was 73.
As high as these athletes' VO2 max values are, humans actually do not fare well against many other mammals in their ability to consume oxygen at a fast rate. Humans' VO2 max is equal to that of the pig and the rat, about half that of the horse and the dog, and only one-third that of the fox. Among all animals, flying insects have the highest rate of oxygen consumption relative to their size. For example, the VO2 of a hummingbird flapping its wings 80 beats per minute is 40 ml/gram/hour which, in human terms, is equivalent to 666 ml/kg/min. As if this were not impressive enough, the flight muscles of worker honeybees, flapping their wings 250 beats per minute, consume 6 ml/gram/min, equivalent to 6,000 ml/kg/min in human terms.
Check out the second article in this two-part series to learn ways to improve VO2 max.race.