If you work out, BMI might not be for you
BMI does not take into account how much of your weight is muscle and how much of your weight is fat. If you are an active individual or an athlete, more than likely you have more weight in muscle than the average person and your BMI may not accurately reflect your fitness level or how healthy and fit you look. Why? Because BMI is merely a correlation between your height and weight. Many active individuals or athletes have a higher than normal weight, despite being active and lean. It's not unusual for a bodybuilder or athlete to have a BMI that indicates overweight or obese, despite the fact that they are lean and fit.
BMI does have some advantages. First of all, it's inexpensive, noninvasive and simple to calculate. All in all, it provides a quick reference for non-active and obese adults, however as someone progresses in a fitness program their body composition changes and BMI may not accurately account for such changes.
Body Fat Percentage and Body Composition (body fat and lean mass)
This is where measuring body fat composition is important. Measuring body composition is literally measuring what percentage of your body is made up of fat compared to lean mass. These numbers give a more accurate representation of fitness and leanness for someone who is physically active.
Why is measuring body fat percentage important?
Most people track their progress by jumping on a scale and hoping for a smaller number. That process can be misleading! Body composition refers to the proportion of fat mass and fat-free mass (muscle, bones, organs) in your body. When you begin a new fitness program you will be decreasing you body fat percentage and increasing your lean body mass percentage with muscle (which weighs three times more than fat does per unit of volume). This is why you may look leaner, but not be losing much weight. Body weight scales can tell you how many pounds you have lost or gained, but they can't tell you how much of that was fat or muscle. By tracking your body composition you can track how much fat you are actually losing and how much lean mass you are gaining.
This is why tracking your body composition is important in any fitness program. We call this "measuring up."
So, ask yourself "How do I look in the mirror?" "How do my clothes fit?" And don't forget to measure up!