Lean body mass is commonly used to describe the muscles in your arms, legs, back, neck and abdomen. But actually it also includes your heart muscle, and the tissues of your other internal organs as well as water, and bone. This is the part of your body you want to preserve or expand.

How much lean body mass you have is the most important factor in determining your metabolism (the rate at which you burn the calories). The higher the amount of your lean body mass, the higher your metabolic rate and the more calories you will burn when you are sitting or lying down. This higher metabolic rate makes it easier to maintain your weight.

Want to build up your lean body mass? The good news is that you can increase the amount and the strength of your muscles through a regular program of strength training — also known as “resistance” training.