Fitness professionals generally describe body composition in terms of two categories: fat body mass and lean body mass. Fat body mass includes all of the body’s fatty tissue, while lean body mass includes everything else, such as the bones, organs, and muscles. Therefore, the term lean muscle refers to the fact that muscle is part of lean body mass. These two components are usually measured in a ratio, or by percentage. Body fat percentage, the amount of the body composed of fat mass, is becoming an increasingly popular way to measure fitness levels.
In previous decades, an individual was generally judged to be overweight or underweight based on how much that person weighed in relation to his or her height. The medical community still uses a measurement called body mass index (BMI) to evaluate a person’s weight and determine if he or she is healthy, or needs to gain or lose weight. BMI is based purely on the measurement of weight, measured in kilograms, divided by the square of the individual’s height in meters. This measurement works as a rough estimate of fitness for the majority of people, but is not accurate or appropriate for some circumstances.
The problem with this measurement is that it leaves no room for very athletic or very sedentary people to have differing body compositions, and therefore differing levels of health. For instance, an extremely sedentary person may be composed of 35 percent body fat with very little lean muscle, and yet weigh the same as a bodybuilder with 6 percent body fat and a huge amount of lean muscle. If these two individuals are the same height, they will also have the same BMI, and will be judged to be at an equal fitness level.
Currently, the fitness industry is heavily populated with products claiming to allow the user to rid his or her body of fat while preserving the lean muscle, resulting in a sculpted, toned physique. This goal is what most fitness trainers and athletes recommend working toward. It is considered to be medically sound advice, because it is much healthier for a person to have a large amount of lean muscle than it is for someone to have a large amount of body fat. Many fitness professionals, doctors, and health institutions readily provide information on what body fat percentage or ratio of fat mass to lean muscle and other lean body mass is healthy for each gender at varying age groups and fitness levels.