This animation shows a comparison of the change in BMI for a given height and varying weights. It also shows why BMI is inaccurate for muscular people. This animation includes audio narration. Body Mass Index, or BMI, is a commonly-used measure of obesity. The animation shows a range of weights at a given height (5' 10"), and shows the points at which a person is classified as "overweight" or "obese." In addition, it shows one of the problems with using a simple measurement of height and weight to determine obesity: a very muscular person can have a BMI that would categorize him or her as obese.