Comparing body mass against your height is a basic anthropometric measurement that is referred to as the body mass index. It was designed to classify healthy and unhealthy weights for general and clinical populations. According to Dr. Vivian H. Heyward, author of "Advanced Fitness Assessment and Exercise Physiology," it gives a wider range of validity than compared with a simple height-weight chart but still has some biases in measure. Using the body mass index equation can supply an estimated idea on how your current weight can affect your health.
Body Mass Index
The body mass index -- or BMI -- is used to classify individuals as obese, overweight and underweight by a ratio determined by dividing your weight in kilograms by your height in meters squared. Dived your body weight in pounds by 2.2 to find your weight in kilograms, and multiply your height in inches by 0.0254 to find your height in meters.
BMI Ranges
According to the World Health Organization, the classes for the BMI are underweight, normal, overweight and three classes of obesity. A BMI value less than 18.5 is considered underweight, a value between 18.5 and 24.9 is considered normal and a value from 25 to 29.9 is considered overweight. Obesity in terms of BMI starts at a value of 30. The classes of obesity are 30 to 34.9 for class one, 35 to 39.9 for class two and 40 or greater for class three.
BMI Biases
The BMI is good indicator for apparent subcutaneous fat and can create health classes for individuals who are mainly sedentary with no other health complications. Dr. Heyward, author of "Advanced Fitness Assessment and Exercise Prescription," reports that BMI is limited as a measurement of only considering body fatness because it does not account for the composition of body weight. According to the American College of Sports Medicine, factors such as age, ethnicity, bone density, lean tissue mass and frame size affect the relationship between BMI and body fat percentage. The BMI, in essence, only considers the weight that you possess to be fat. The BMI can result in misclassifications for people who exercise regularly, athletes, amputees and people with osteoporosis, for example.
Body Composition
There are other ways to measure the health of your body composition that break down the percentages of lean body mass, bone mass and adipose fat tissue. A common device is skin fold calipers. These will be used by a trained professional who can determine the percentage of fat composition in your body through readings on several skin-fold sites. There is also a device called the BIA -- or bioelectrical impedance analysis -- which sends an electric current through your body to find your body composition. The accuracy of this device can be severely altered by your hydration level, reports Dr. Heyward. There are three other methods to determine percentages of body mass accurately, but these methods are costly and time-consuming. They include hydrostatic weighing, dual energy X-ray absorptiometry and the BOD POD.
References
- "ACSM's Guidelines for Exercise Testing and Prescription, 8th edition.;" American College of Sports Medicine; 2009
- "Advanced Fitness Assessment and Exercise Prescription, 5th ed.;" Vivian H. Heyward; 2006
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