The Fitness and Strength Experiment: Measuring Muscle Mass

There are 2 readily available ways to measure muscle mass and numerous ways to estimate it. To measure muscle mass directly, the 2 readily available methods are BIA (Bio-Impedance Analysis) and DEXA (Dual-Energy X-Ray Absorptiometry) scanning. The BIA method uses an electrical charge to estimate muscle mass throughout the body. It is relatively easy to do and reasonably accurate as long as you use a machine that has been properly calibrated as you would find at a doctors office and in some fitness gyms. The DEXA method is much more accurate especially at extremes of height and weight. We use the DEXA method regularly on all of our patients, but most of you performing this experiment will not have ready access to it. If you do, we recommend using it as your gold standard for muscle mass.

Once you have your muscle mass calculated, we recommend calculating the skeletal muscle index using the following method:

1. Take the muscle mass in kg of the 4 limbs (the appendicular mass).

2. Divide that by the square of the height in meters.

3. This is called the skeletal muscle index or SMI.

An SMI of 5.5 for women or 7.0 for men is considered a sign of low muscle mass and is the main criteria used to diagnose Sarcopenia (the condition of low muscle mass). We try to maintain our female patients above 6 and our male patients above 7.5 at all times. Many of our patients well exceed this.