The Equation Of Body Mass Index

The equation of body mass index or (BMI) is used to assess a person's weight as it relates to height. It is also known as the Quetelet index and has been used to identify and evaluate the averages of overweight and obesity since the 19th century. It is considered to be one of the most basic body composition assessment tools used in the health, fitness and medical industries.

History

The equation of BMI or Quetelet index was created by Adolphe Quetelet in 1835. He was the first in the physical sciences to use the bell curve in creating and comparing averages as they compared to human traits. Quetelet used his idea of the average man as his central value and then created groupings from that value. Today, it is known as the international measure of obesity where, QI >30 is obese.

Equation Identification

The equation of BMI is calculated by dividing an individual's body weight in kilograms by his height in meters, squared. If a person is more comfortable with English measurement units he can find his BMI by multiplying his body weight in pounds by 703 and dividing by his height in inches, squared. Today, charts, graphs and calculators are available to help calculate index numbers with ease.

Interpretation of Numbers

For adults 20 years of age and older, index numbers are interpreted by standard weight categories and are the same for both males and females. If your BMI number is less than 18.5 you are underweight, 18.5 to 24.9 is classified as normal, 25 to 29.9 is considered overweight and a BMI greater than 30 is considered obese. The American College of Sports Medicine and the Centers for Disease Control and Prevention both use this classification system in describing index numbers to their clients. Recently ACSM has added a class II and III in the obese weight section. With BMI numbers growing larger better classifications are needed in order to help health and fitness professionals describe disease risks to their clients.

Considerations

The BMI equation is not a diagnostic tool, meaning that being overweight or obese does not mean that you have high blood pressure, cholesterol or another illness. If you have a high BMI number then you should consult with a health professional to assess your situation. BMI also fails to distinguish between body fat, muscle mass and bone mass; meaning that an individual with an acceptable body fat percentage with a larger frame may be considered obese because of higher muscle and bone mass which in return makes him weigh more.

Use

The equation results are used to screen for potential health problems in individuals. ACSM found direct correlations to BMI numbers greater than 30 and chronic illnesses such as high blood pressure, high total cholesterol levels, low high-density lipoprotein (HDL) cholesterol levels and various cardiovascular diseases. Even though this equation may not be the most accurate, using it is simple and fast, which allows professionals to screen large populations of people at one time and help encourage them to make healthy lifestyle changes depending on their BMI equation results.