Is BMI a good way to track muscle mass?

Unfortunately, BMI (body mass index) is not a very good indication of fat mass or muscle mass. BMI is height-to-weight ratio that is calculated by dividing your weight in kilograms by your height in meters squared. Due to this, BMI does not differentiate between fat and muscle because that is not what it was intended to do. BMI is meant to be a simple calculations to be an indicator of obesity. If someone has a BMI of over 35, they are at severe risk of obesity-related diseases. When calculating the BMI of someone with large amounts of muscle mass, the results becomes inaccurate because it will classify them obese. A better way to track body fat is with skin fold calipers. The calipers estimate the percentage of fat mass that is in the body. You can multiply this percentage by your total body weight to determine the number of pounds of fat you have in your body.
Eric Beard
Sports Medicine
Body Mass Index (BMI) is not a good way to track muscle mass. BMI is calculated from the relationship between a person's weight and height. It provides information on their amount of weight a person carries relative to their height. BMI does not take into account lean body mass vs. fat mass. Body composition tests (body fat tests) are a much more effective way to assess and track changes in muscle mass. Hyrdostatic or under water weighing is the most accurate (as well as the most uncomfortable way) way to assess body composition and muscle mass. Skinfold calipers can be accurate when used by someone who has been trained properly and has significant experience using the calipers. Hand held devices such as bioelectrical impedence can provide accurate readings provided the user is hydrated and the readings are performed at the same time of day as the original test.
Wendy Batts
The BMI formula uses height and weight in its calculation, but it can’t tell whether the weight comes from muscle, fat or other body tissues. For that reason, Body Mass Index is not the best way to track muscle mass.

Usually body composition tests are a better way to track changes in muscle versus fat tissue. For example if I am 200 pounds and my body composition measurement is 10%, this means that I carry 20 pounds of body fat and 180 pounds of lean, or fat free, mass (made up of muscle, bone, organ tissue, nervous tissue, etc.). If I were still 200 pounds and was then 5%, then I would be carrying 10 pounds of body fat mass and 190 pounds of lean mass. Since we can assume that I didn’t make significant gains in organ or bone tissue then it’s a pretty safe bet to say that the 10 pound jump in lean mass was due to an increase in muscle.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.