BMI treats all weight equally, but athletes have significantly more muscle mass than average. Since muscle weighs more than fat by volume, a 200-pound athlete and a 200-pound sedentary person of the same height will have the same BMI despite very different body compositions.

Many healthy athletes have BMIs of 25-30, technically 'overweight,' due to muscle mass. Body fat percentage is a far better metric for athletes — male athletes typically range from 6-15% and female athletes from 14-25% depending on sport.

Athletes should track body fat percentage, lean body mass, waist-to-height ratio, and sport-specific performance metrics rather than relying on BMI. DEXA scans, hydrostatic weighing, or calibrated skinfold measurements provide much better body composition data.