The skeletal muscle mass was one I had to look up. It isn't your skeletal bones, but all the muscles attached to your bones. Men on the average are in the 30% range depending on age. Unless you work out you begin to lose muscle mass at around age 40. Mine is 48% meaning almost have my body weight is muscle a plus as I age. On the other hand, I'd probably be 20 pounds or more lighter in the normal range. I'll take the muscle. :thumbsup: