Body Mass Index (BMI) - How Accurate?

Body mass index (BMI) or Quetelet Index is a widely-used statistical measure of a person's weight in proportion to height. It was invented over 100 years ago, and is frequently used in assessing the fitness level of individuals or populations. The BMI calculation renders a value called a BMI Index that is used to rate how close a subject is to the "ideal" weight.

For example, surveys that show the increasing levels of obesity in America are usually based on BMI index, as follows:

BMI > 30 = OBESE

BMI 25-30 = OVERWEIGHT

BMI 18-25 = NORMAL

BMI < 18 = UNDERWEIGHT

How does the calculation work?

BMI is calculated as 703 * (weight in pounds / height in inches squared).

So, for a person who is 5'10 and weighs 200 lbs, the BMI would be calculated as follows:

703 * (200 / 4900) = 28.7... This person would be considered OVERWEIGHT, nearly obese.

There are, however, problems with this formula. One of the problems is that there can be a substantial variance in what constitutes "ideal weight" from person to person. For example, the BMI calculation does not take into account persons with dense muscle mass. So, someone who does extensive strength training and has developed muscle mass may in fact have a BMI that indicates he or she is overweight even though the person may be very fit with low body fat.

In fact, we know several extremely fit people with BMIs in the high 20s, but whose body fat is approaching the level of professional athletes! Their body weight is relatively high in proportion to their height because they carry substantial muscular weight.

So, how useful is the BMI indicator?

The BMI index is not a one-size-fits-all wellness indicator. And like any other measure of fitness it needs to be used within context, along with other metrics such as blood pressure, cholesterol level, body fat percentage, and cardiovascular efficiency.

If your BMI is outside the "normal" range, it's a good idea to assess your other fitness metrics when determining whether you are at your ideal weight. But as with any other fitness metric, BMI can be misleading or even useless when evaluated in a vacuum.

Pete Bellisano is a certified personal trainer and owner of Peak Performance Fitness in Berkeley Heights NJ. Peak clients are achieving outstanding results losing weight and improving overall fitness, through our unique approach to Fitness For Real People. Visit our site to see what our clients have to say about their success, and to pick up your free fitness info. http://www.peakperformancenj.com

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