Define Body Mass

You have likely heard the term "body mass" used frequently in reference to health and fitness. Your health care provider may have calculated your body mass index, or your personal trainer may have commented on your lean mass. However, many people are uncertain about the true meaning and importance of body mass, and how it applies to them.

Lean Mass

Your total body mass can be divided into two categories: fat mass and lean mass. Your lean mass includes muscle, bone and any other body parts which are not fat. Lean tissue is metabolically active. That is, lean tissue is living tissue, and there are a number of metabolic functions being carried out within lean body cells around the clock. You can think of lean mass as your metabolic furnace. The more you have, the more calories you will burn each day.

Body Fat

Unlike lean mass, most of your body fat is storage fuel. There is minimal metabolic activity in your storage fat cells. Excessive body fat is dead weight that does not contribute to joint movement and will weigh you down. However, some stored fat is desirable, and some body fat is essential to maintain overall health. Essential body fat provides insulation and protection for your vital organs, stores fat-soluble vitamins, and contributes to your hormonal balance. Subcutaneous fat plumps out your skin, helping to maintain a youthful appearance.

Measuring Body Mass

An individual who is muscular with high bone density will have a lower body fat percentage than a high-fat individual of the same height and weight. There are a variety of methods available for determining your body fat percentage. The most user-friendly are smart weight scales or hand-held bioimpedance devices. While easy to use, these methods are sometimes less accurate than a skin-fold caliper or hydrostatic (underwater) weighing. According to the American Council on Exercise, the recommended body fat percentage for average women is 20 to 24 percent and 14 to 17 percent for average men. For athletes, it is about 20 to 30 percent lower. Your body mass index, on the other hand, is derived by a mathematical formula which divides your weight in kilograms by your height in meters squared. By National Institutes of Health standards, a body mass index of over 30 categorizes you as obese, 25 to 29.9 as overweight and 18.5 to 24.9 as normal.

The Trouble with BMI

The trouble with BMI is that it does not take into consideration your lean muscle mass or bone density. This becomes problematic when dealing with athletic populations. If you consider BMI alone, many gold medal Olympians would be categorized as overweight, despite the fact that they are lean and muscular. Even if you are not a world-class athlete, if you exercise regularly, you may not score well on the BMI scale.

Weight Versus Body Mass

Most personal trainers will agree that the scale is not the best way to measure a client's progress. This is because clients often drop several clothing sizes without shedding many pounds. To get a better grasp of this phenomenon, think of the marshmallow and the peanut. They both weigh about the same. Yet, the peanut is tiny and dense while the marshmallow is big and fluffy. Your lean mass is like the peanut, and your body fat is like the marshmallow. Instead of just trying to lose weight, focus on increasing lean mass and bone density, You will have more energy, be stronger, have healthier bones, and burn more calories all day long.