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Body mass index - Wikipedia, the free encyclopedia
The BMI is meant to broadly categorize populations for purely statistical purposes. As noted, its accuracy in relation to actual levels of body fat is easily distorted by such factors as fitness level, muscle mass, bone structure, gender, and ethnicity. People who are mesomorphic tend to have higher BMI numbers than people who are endomorphic, because they have greater bone mass and greater muscle mass, respectively, than do endomorphic individuals.
Similarly, ectomorphic individuals could conceivably receive a reading below the normal range, when in fact their body type makes it healthy for them to be thin. In fact, ectomorphs could obtain healthy readings even when their body fat percentage is higher than is healthy, as their low lean mass will lower the BMI.
People with short stature tend to have lower BMI. Therefore they should use a lower cut-off value for obesity diagnosis. The same applies to older people, whose reduced muscle mass can hide additional body fat without increasing BMI. Therefore, find out what your body fat is to work out if you are in the healthy BMI range.