*Geek Box: Melatonin, “Circadian Time” and “Clock Time”
Bioelectrical impedance analysis [BIA] is a method of assessing body composition and additional parameters, such as body cell mass, based on resistance within the body to an electrical current. In effect, BIA may provide a measure of the volume of a solution based on its colligative properties, i.e., the properties of molecules binding together. As such, the measures of body composition and cell mass are not direct measures of these compartments, but estimates derived from equations that require age, sex, and ethnicity-specific equations to provide such estimates.
The “phase angle” [PhA] is a parameter calculated from bioelectrical impedance data using its own specific equation and is based on appendicular impedance, i.e., of the leg and arm. Given the characteristics of appendicular lean soft tissue, PhA is considered a measure of skeletal muscle cell quality, and higher values reflect higher muscle cell quality.
PhA has shown strong correlations with muscle strength and correlates with nutritional status in patients with chronic diseases. As such, PhA derived from BIA has been attractive for conditions such as sarcopenia and in clinical nutrition contexts as a non-invasive measurement method. The ideal phase angle values range between 5–9 degrees, depending on the age and sex of the individual.