Body Mass Index (BMI) is another popular way to determine whether someone is at a "healthy weight." Like the height and weight charts, BMI is a poor measure of fitness because it doesn't take into account fat versus lean tissue.
According to the textbook, Physiology of Sport and Exercise by Wilmore and Costill, BMI is defined as, "A measurement of body overweight or obesity determined by dividing weight (in kilograms) by height (in meters) squared."
The text says you are considered overweight if you're female with a BMI is 27.3 or greater or if you're male with a BMI of 27.8 or higher. It also says that BMI correlates highly with body composition and is a better indicator of fitness than your weight alone. (It even says you're more likely to die if your BMI is 25 or greater).
I'll buy the part about BMI being better indicator of health and fitness than body weight alone, but the part about BMI correlating well to body composition is complete hogwash!
Let me show you an example of how BMI falls short as a measure of body composition.
In the off-season, I weigh about 201 lbs. and I am 5' 8 inches tall. Converted to metrics, 201 lbs. is 91.36 kilograms and 5' 8" is 172 cm or 1.72 meters. So now let's plug my stats into the BMI formula and see what we come up with...
1.72 meters squared = 2.96 meters
If we judge my physical condition according to my BMI of 30.86, then I'm a serious health risk and I need to lose some weight. Obviously, that's not the case. Even when I'm not in a pre-competition mode, my body fat seldom goes into the double digits (it was 8.7% last time I had it measured.)
Body builders and other athletes carry more lean body mass than the average person and will therefore be classified as overweight if BMI is used as the criteria for measurement. Conversely, someone could have a "healthy" BMI of 19 to 22 and yet have a dangerously high level of body fat (a "skinny fat person").
Shape up America, the anti-obesity campaign started by Dr. C. Everett Koop, recently published a statement pointing out the shortcomings of BMI. According to the Shape up America website, BMI misclassifies one out of four people and should not be used by athletes.
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