The primary reason to measure body composition is so you can distinguish between fat and muscle. Instead of looking only at body weight, the body composition test lets you focus on body fat and lean body mass. Another reason to measure your body composition is so you can monitor your progress and get continual feedback. As you learned in chapter one on goal setting, it’s critical to have a way to objectively measure your progress. A weekly body composition test allows you to measure and record the exact effect your nutrition and exercise program is having on your body.
Many people mistake activity for achievement. They are apparently dieting hard and working hard in the gym – the problem is, they’re getting no results and not even noticing because they’re not measuring results! Many people are climbing the ladder of success every day, only to find that it is leaning against the wrong wall! If you don’t measure your results with body composition testing, you could be spinning your wheels (burning up energy but going nowhere), or even heading in the wrong direction!You might be busy, but without the constant feedback that body composition testing provides, you have no way of knowing if all that activity is moving you closer to your target. The only goals worthy of your effort are fat loss and muscle gain, not weight loss and weight gain. For example, if you’re losing weight but the type of weight you’re losing is muscle, then you’re headed in the wrong direction and you need to change your program!
If you’re losing fat and maintaining your muscle, then your program is working and you shouldn’t change a thing.
Body Muscle Workout Guide 