During the bioelectrical impedence measurement, you will be asked to stand barefoot on what looks like a weighing scale and grip a portable handle in each hand for a period of 30-40 seconds.
Bioelectrical impedence measures the resistance of body tissues to the flow of a small, harmless electrical signal. The current is so low that you will not feel any sensation from it.
The proportion of body fat can be calculated as the current flows more easily through the parts of the body that are composed mostly of water (such as blood or urine) than it does through bone or fat. It is possible to predict how much body fat a person has by combining the bioelectric impedence measure with other factors such as height, weight, sex, and age.