The most common criticism of the BMI is that it cannot tell the difference between fat and muscle. Because muscle is denser than fat an athlete’s BMI might indicate that he is overweight, but that extra weight might be composed more of muscle than fat.
Olympic trainers take these systems into account. A long-distance runner should use aerobic metabolism for as much of her ATP as possible. To ensure this, she’ll be tested on a treadmill to measure her threshold of aerobic metabolism.