One way to determine how fit you are is to measure how much oxygen your
body can efficiently consume-a measurement of how hard your muscles are
working. Your VO2 max is the measurement of how much oxygen you consume
in a minute, while exercising at sea level. The greater your oxygen consumption,
the better your cardiovascular health.
Hospital fitness programs measure a person's VO2 max by having a person
exercise under conditions that push the heart's ability to deliver blood
to its maximum. For instance, you might run on a treadmill that increases
in speed and/or steepness at regular intervals. While you are exercising,
you breathe out through sensors that measure air volume and oxygen concentration.
Computer analysis determines how much oxygen your body is using. As the
workload increases, so does your oxygen consumption-up to a point. At that
point, exercising harder shifts the muscles into anaerobic activity. Soon
after this point, the muscles will fatigue and you will have to stop exercising.
VO2 max can be expressed as an absolute number-the number of liters of
oxygen a person consumes in a minute. Or it can be expressed as a relative
number-the number of milliliters of oxygen a person consumes in a minute
divided by the person's weight in kilograms.
The average relative VO2 max of an untrained man in his mid-30s is about
4045 ml/min/kg. After an endurance exercise program, that same man
might have a VO2 max of 5055 ml/min/kg. An Olympic champion 10,000
meter runner might have a value approaching or over 80 ml/min/kg. And if
you think jockeys just get to go along for the ride while their horses do
all the work, think again. One study found that a jockey's VO2 max can be
as high as 69 ml/min/kg.