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Body Mass Index

Brian Bambl, B.S. Exercise Science 2010-02-23

BMI, which stands for Body Mass Index is a calculation that compares how much you weigh relative to your height.  BMI is a quick and easy way of assessing whether or not you’re at a healthy weight.  It only requires that you know your height and your body weight.  BMI can be calculated using a metric formula,

(body weight in kilograms/(height in meters^2)) or using an imperial  formula,

(703 * weight in lbs./(height in inches^2)).  CLICK HERE TO USE OUR BMI CALCULATOR

 BMI is a very simple measurement and has become the most frequently use method by health care professionals in assessing whether or not an individual is at a healthy weight.  However, before using your BMI as your sole piece of information in determining whether or not you’re at a healthy weight, let’s first put BMI in perspective.  BMI only takes into account your height and weight, so the amount of body fat can vary from individual to individual despite two people having the exact same BMI.  This is a major reason why BMI can sometimes be misleading and inaccurate in assessing a person’s weight. 

High BMI’s for individuals with low body fat are often the case when looking at athletes who typically possess a large amount of muscle mass and therefore end up weighing more than the average individual at their height.   For example, Cael Sanderson a 4 time NCAA wrestling national champion and Olympic gold medalist would have be considered to be overweight in the 2004 Olympics based on the BMI scale.  In the 2004 Olympics he wrestled at 184.8 lbs and is 6’0” tall.   This height and weight gives him a BMI of 25.1, which barely places him in the overweight category.  This of course is ridiculous since his body fat percentage at the time was probably somewhere around 5 to 7%.  This goes to show that for very muscular lean individuals, that BMI will often place them in the incorrect category. 

Low BMI’s for individuals with high body fat are less common, but there are some people who fall into this category.  This is more common among inactive individuals who possess very little muscle mass.  For example, a female who is 5’ 8” and weighs 135 lbs would appear pretty lean, but may have a body fat percentage of 33%.  At this height and weight she would have a BMI of only 19.8, which would place her at the low end of the healthy range for BMI.  However, her body fat percentage would place her above the healthy body fat range for females (20% to 32%). 


Despite the fact that BMI is not a perfect measurement it is a good place to start when assessing your body weight.  If you’d like the most accurate assessment of your weight then you should have your body fat percentage checked.

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