The body weight alone is not significant. The same weight can be made up of a large amount of muscle and little fat, or of little muscle and a lot of fat. The weight, or changes to the weight, should always be assessed under consideration of the proportion of body fat.
The BMI is the quotient of weight and height squared. It serves towards classification of one's weight.
As before, the BMI is still used to assess the risks of diseases that accompany overweight, but this is controversial, because it takes neither the ratio of fat to muscle, nor the fat-distribution pattern into account. For example, someone with a high proportion of muscle can have the same BMI as a person with a high proportion of fat. In order to assess overweight, it is better to consider the percentage of fat and the Waist to Hip Ratio.
Body fat and lean mass are represented in both absolute (in kg) and relative (in %) values. The relative proportion of body fat is the percentage of stored fat in relation to the overall mass (weight). It is used to assess the level of overweight. Healthy women have a higher proportion of body fat than healthy men, therefore the normal ranges for body fat are gender-dependent.
Together with the Waist to Hip Ratio, the proportion of fat gives an indication of the risk of metabolic diseases (e.g. cardiovascular disorders, diabetes) – the higher the proportion of fat, the higher the risk.
Together with the weight and the lean mass, the body fat serves, above all, as a means of assessing appropriate workout or nutritional programs (in the analysis of two concurrent scans). For a muscle-building workout, the fat can be lost, although the weight might remain constant/increase, because more lean mass (muscle mass) is built up. The opposite can happen in the case of a diet – the proportion of body fat might remain similar, although the weight and the absolute body fat are reduced. This happens when the lean mass is also reduced.
The body fat calculations have the advantage of being very precise in terms of repeated measurement. Tracking of changes over time are highly valid. But note that the body fat data is based on calculations derived from scientific studies. These calculations are to be seen as estimates of the "true" values. The "true" values can only be determined with equipment that is too expensive and complicated for the fitness industry.
The lean mass is inversely proportional to the fat mass. Changes to this value are mostly the result of a change in muscle mass, or stored water. The latter can be influenced by nutrition (especially by carbohydrate intake). In order to determine whether the changes mostly affect the muscles, it is important to check whether or not the client has changed his/her diet. If not, the changes are most likely to be in the muscles.
RMR – Resting Metabolic Rate (Calorie Basal Metabolism)
The basal metabolism indicates the number of calories (kcal) that are required over a 24-hour period, in order to sustain the bodily functions at rest. This is influenced by gender, weight, height and ratio of muscle to fat, among other factors. Besides the basal metabolism, the active metabolism is the additional amount of energy used daily, due to physical activity. The more intensive and comprehensive the activity, the higher the active metabolism. Together, the basal and active metabolism indicate the overall energy used by a person. Based on the energy used, recommendations can be made regarding the number of calories that should be consumed.
WHR – Waist to Hip Ratio (Health-Compromising Body Fat)
The WHR indicates the ratio between the circumference of the waist and the hips. This ratio is used to assess the distribution of fat tissue deposits. A high proportion of fat around the waist is characterized by a waist-circumference similar to, or even larger than, the hip circumference. This waist-heavy fat distribution (so-called visceral fat) indicates an increased risk of metabolic disease (e.g. cardiovascular disorders, diabetes). It is recognizable by the so-called "apple shape". On the contrary, the so-called "pear shape", which is less of a risk, is characterized by more fat deposits around the hips. Scientific studies have defined gender-specific threshold values for the assessment of an increased risk of metabolic disease. A value that falls within the red zone of the scale indicates that the customer should be put onto a fat-reduction program.