Intro to key Body Composition terms
A professional body composition result sheet can appear intimidating at first glance, with a lot of terminology and lingo that may seem confusing.
This article will explain what the key body composition terms found on a result sheet mean in plain and simple language, making it easier for you to get insights into your health!
Percent Body Fat (PBF)
Bioelectrical Impedance Analyzers are sometimes referred to as "body fat scales", because this is the output that many people care the most about, understandably!
This is the percentage of body fat is in your body, calculated by dividing the weight of body fat mass by total weight. Although there are no universal standards for under, normal, or over, some commonly used standards for "healthy" body fat are 10-20% for men and 18-28% for women. Other commonly found standards are those used by the American Council for Exercise (14-24% for men, 21-31% for women), or those where you have different recommended standards for different age groups.
Generally speaking, it is recommended to keep PBF within normal range.
Body fat can be simplified into two types - the fat underneath your skin that is readily visible from the outside (subcutaneous fat), and the fat around your abdomen wrapping around the internal organs (visceral fat).
Visceral Fat is important to track because although you can't see it externally, it is highly correlated with risk of obesity-related diseases! Generally speaking, it is best to keep Visceral Fat Area lower than 100.0 cm2 (or less than Level 10 for Visceral Fat Level) to reduce health risks.
Soft Lean Mass
This is the weight of all the muscle in your body. Note that this isn't what most people refer to when they talk about "building muscle" - in most cases, they are in fact thinking of "skeletal muscle mass" (detailed below). Soft Lean Mass refers to the various types of muscle including cardiac muscle, smooth muscle, and skeletal muscle.
This is an important distinction to understand because analyzers from different brands may not all use the same terminology. Some devices may use "muscle" to refer specifically to "skeletal muscle", and comparisons will be inapplicable if you try to directly compare the two!
Skeletal Muscle Mass
This is the muscle used to move the body/skeleton, hence the name. In contrast to other types of muscle, it can be consciously controlled and developed actively through nutrition and training, which is why it is used as the main muscle indicator.
As noted above, most people use the word "muscle" to refer to skeletal muscle. Skeletal muscle mass typically correlates with strength and muscular body type. As such, a common goal is to develop it to the higher end of "normal" or even "over".
Whereas "Muscle Mass" refers to the amount of muscle in the body, "Muscle Quality" refers to strength. A commonly used strength assessment method is grip strength, which has been found to be representative of total body strength. Why is it important to estimate and assess strength?
Generally speaking, muscle strength declines faster than mass in elderly populations. Therefore, monitoring muscle mass is important but insufficient for detection of sarcopenia - routine strength assessments are also essential!
If strength measurement or projection consistently declines, that is an important warning sign of potential sarcopenia, which can help lead to earlier treatment and training to address the problem. This is particularly useful in long-term care, rehabilitation, and other fields where muscle quality is a valuable metric to track.
Basal Metabolic Rate
Basal Metabolic Rate (BMR) is basically the number of calories your body needs to burn each day (24h) to maintain itself. This is an important output relating to gaining, or losing weight. All else being equal, a person with higher muscle mass will have a higher BMR compared to someone with less muscle mass.
To lose weight, a person needs to burn more calories than they consume, and vice versa. By multiplying your BMR with Physical Activity Level (PAL), you can get a general estimate of Total Energy Expenditure (TEE), which is the amount of energy you actually expend each day, since in addition to BMR, activities such as movement, thinking, digesting food, etc. also consume energy.
Common PAL typically ranges between 1.2 for sedentary desk jobs with little to no physical exercise, and 1.5 for moderate exercise/sports.
Total Body Water
The body is mostly comprised of water, contained in the blood, organs, muscles, and elsewhere. Body Water can be subdivided into intracellular water and extracellular water. Because muscle is high in body water, highly muscular people tend to have more body water than normal, but this is not cause for concern, as Edema (excessive body water) is about the proportion of body water, not total amount.
Intracellular Water and Extracellular Water
Body Water is divided into Intracellular Water / ICW (water inside the cells) and Extracellular Water / ECW (water outside the cells). This is an important indicator of body water balance - various illnesses are correlated with excessive ECW, defined as ECW/TBW (Edema Index) ratio exceeding 0.39.
Phase angle is a bioelectrical impedance measurement that is used as an indicator of cellular health, and is particularly important because body composition outputs such as fat or muscle don't tell the entire story about health. Two people can have the exact same BMI, Body Fat, and Muscle - but they aren't necessarily equally healthy!
Generally speaking, a higher phase angle means healthier cell membranes. So if a person's phase angle consistently decreases, that could be a sign of more serious condition causing this change.
Bioelectrical Impedance Vector Analysis (BIVA)
BIVA compares bioelectrical Reactance (Xc) and Resistance (R) with others of the same age, gender, and ethnicity, making it possible to evaluate hydration and cellular status
The three ellipses correspond to results for the comparison group. 95% of people's results fall within the outside ellipse, 75% within the second ellipse, and 50% within the innermost ellipse. In other words, the further out the measurement point, the more abnormal the result. Tracking change in the measurement point's location is an important way to observe abnormality.
We hope this article has been useful in unpacking some key body composition terms and how to make use of them! Please check out the linked articles to explore each measurement in more detail!