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When it comes to using BMI for athletes, the calculation may be a less accurate measure of body fat than it is for most of the general population. Because muscle is denser than fat, it weighs more. As athletes tend to be muscular, using BMI to assess their weight may result in overestimating their true level of body fat. Instead of using BMI for athletes, doctors may use other methods of assessing levels of body fat, including skinfold thickness measurements, underwater weighing, and bioelectrical impedance.
The BMI (body mass index) score is valid for both men and women, but it does have some limits. One of these limits involves the accuracy of using BMI for athletes. Using BMI for athletes can overestimate their level of body fat because muscle is denser than fat and weighs more. Therefore, an athlete's body fat can be normal or even low, but the person may have a high BMI. This does not mean that they are unhealthy or overweight. In fact, a number of gold medal winning athletes at the Olympics would be considered obese based solely on their BMI.
However, keep in mind that just because someone is an athlete does not mean that they cannot be overweight or obese and at risk for developing medical conditions related to obesity (such as type 2 diabetes and heart disease).
BMI is used as a screening tool to identify possible weight problems for adults and children. However, there are a number of different ways to measure body fatness. These other methods used to measure body fat include:
- Skinfold thickness measurements (with calipers)
- Underwater weighing
- Bioelectrical impedance
- Dual-energy x-ray absorptiometry (DXA)
- Computerized tomography.
These other methods of measuring body fatness are more accurate than BMI, especially in athletes. For an athlete with a high BMI, one of these alternative methods is recommended.