3. Lean Mass This is everything else that makes up your weight. It includes muscle, bones, organs, water, and all non-fatty tissues. Again, there is a gender difference. Thanks to much higher levels of testosterone, men have a greater amount of muscle mass than women. One pound of muscle takes up much less space than one pound of fat. So, as you exercise consistently and build up strength, your total body weight may actually increase. This can be confusing (and sometimes scary), but you are gaining muscle, while maintaining or even losing fat.
4. Fat Distribution Ever notice how some people can have big bellies but lean legs? Women store most of their fat in their thighs, hips, and butt. These are examples of fat distribution, which refers to where your body typically stores the fat that you have. This is important because where you store fat can be a predictor of health risk. "Apple" shapes (fat storage around the belly) have been shown to have a higher risk of certain cardiovascular diseases, whereas storing fat in your lower half, known as a "Pear" shape, is actually a healthier site for fat accumulation.
Look for gains: Your lean mass can be calculated by subtracting your total fat (as a percentage or in actual pounds) from your total weight. This number will probably be relatively stable, or increase over time, as long as you are exercising. Gains in muscle mass will increase your metabolism, thus enabling you to burn more calories during every activity—even sitting! So, while you do want to lose fat, setting a goal of increasing your muscle mass will help you get there.
Whatever your fitness goal, measuring body composition will help you track your progress, not to mention leave little doubt that all those little (and sometimes big) changes you’ve made are moving you in the right direction. Bottom line: If your goal is fat loss, then measure progress by decreases in body fat percentage, and possibly improved fat distribution. If your aim is to increase strength, then lean body mass will tell you how much muscle you have gained. Breathe a sigh of relief, number-crunchers. These are the only numbers you need to help you meet your goals.
Room for improvement: Changes in fat distribution happen when you are losing fat and building muscle. Typically, the body burns fat all over, and just as typically, fat in the stomach is usually the last to go. There are no exercises you can do to speed up fat burn in any particular area. Cardio activity, utilizing large muscle groups, burns fat all over the body. So, don’t waste your time doing lots of crunches to lose the belly fat, or boxing to lose your arm jiggle. You can measure these changes with a simple tape measure, or just by how your clothes look and feel.