When the long hours you spend in training pay off with low body fat and toned, sculpted muscles, you feel pretty good about yourself. That is, until you assess your body mass index, or BMI.
For athletes and fitness enthusiasts, BMI can categorize you as overweight or obese, even though you are in better shape and have lower body fat than your nonathletic friends.
Women athletes should fall into the range of 12 to 22 percent body fat and male athletes, 5 to 13 percent.
What Is BMI?
According to the Centers for Disease Control and Prevention (CDC), BMI is a measure of weight adjusted for height, calculated by dividing your weight in kilograms with your height in meters squared. BMI measures excess weight rather than excess fat, and provides an easy, noninvasive and inexpensive means of classifying individuals into weight categories.
The CDC concedes that BMI does not calculate your body fat and should not be used as a diagnostic tool to assess health, but rather as an indicator of potential health problems. Curious? You can check your BMI on an online BMI calculator.
BMI for Athletes
If you are athletic, you are likely to be more muscular and have higher bone mineral density than a sedentary or nonathletic person, and that adds up to extra pounds. When you put your weight into the BMI equation, you may get a value greater than 25 percent, putting you in the overweight category, or perhaps greater than 30 percent, classifying you as obese. The CDC admits that some athletic individuals may have a high BMI but a low percentage of body fat.
Use Your Waist Circumference Instead
ACE Fitness claims that BMI is not useful in assessing body builders or those with athletic muscular individuals and is not a good indicator of changes in body composition. Harvard Health Publishing says to take out your tape measure and measure your waist circumference instead. Over 35 inches for women or over 40 inches for men is not great and puts you at risk for disease.
BMI Versus FFM
Your fat free mass, or FFM, includes your muscles, bones, connective tissue and other not-fat components of your body mass. According to exercise scientist Len Kravitz, Ph.D., of the University of New Mexico, we all need a certain amount of fat to maintain good health, and women need more than men.
When you subtract your FFM from your total body mass, you get your fat mass. Body composition is a measurement that compares your fat mass to your total body mass, expressed as percent body fat.
Better Than BMI
Body composition gives an athletic individual a more accurate profile than BMI of health status in relation to weight because you are measuring fat and not just weight. The "gold standard" of assessing body composition is underwater weighing, which can be expensive and inconvenient.
Less expensive and more convenient methods are skin fold measurements, and bioelectric impedance using a hand-held device.
Of the two, skin folds provide a more accurate assessment for athletes, according to Kravitz, because bioelectric impedance tends to overestimate percent body fat in very lean individuals. A qualified fitness professional can do a skin fold assessment for you.
Desirable athletic ranges of body fat are 5 to 13 percent for men, and 12 to 22 percent for women. Optimal fitness values are 12 to 18 percent for men and 16 to 25 percent for women.