College athletes with an elevated body mass index often have a high upper arm muscle area, but not elevated triceps and subscapular skinfolds

Body mass index (BMI, calculated as kg/m2) is increased by high amounts of both lean and fat tissue. Therefore, a very muscular individual with low body fat could be classified as overweight by BMI. To evaluate this problem, the relationship between BMI, body fat as indicated by the sum of triceps and subscapular skinfolds, and muscle mass as indicated by upper arm muscle area (UAMA) was studied in 107 male and 106 female National Collegiate Athletic Association Division III athletes. Sex, the sum of triceps and subscapular skinfolds, and UAMA were significantly related to BMI (overall P<.0001, R2=0.617), although the relationship was nonlinear and more complex in females than in males. Thirty-eight athletes had a BMI of 25 or higher, indicating overweight or obesity. Of these, only four had excess body fat, as indicated by a sum of triceps and subscapular skinfolds greater than the 85th percentile, but 27 had high muscle mass, indicated by a UAMA greater than the 85th percentile. In the nonrandom sample of athletes we studied, BMI frequently classified muscular individuals who did not have high skinfold measurements as overweight.