A body analysis scale is an instrument resembling a bathroom scale that estimates the percentage of fat in the body. It uses a small electrical current that enters the body through bare feet. The body's density is measured by the current, and the body fat percentage is determined based on the body density measurement.
Analyzing body fat and body density are more accurate tools in understanding a person's health than weight alone. This is because fat weighs less than muscle and bone, so it's possible for a person with a high percentage of body fat to weigh less than someone with a high percentage of muscle. In the past, it was not possible to accurately measure body fat percentages with a home device. One common method involved weighing a person, and then submerging him in a tub of water to be weighed again. The higher a person's body density, the lower that person's fat percentage.
A newer method of measuring body fat is called body impedance analysis. Before the invention of the body analysis scale, the procedure was generally done in a clinical setting. The person would lie prone on a cot with electrodes attached to the hands or feet. A 50 kHz current sent through the body measured the density of the tissues by the amount of water contained in them. This method is quite accurate because fat is only 10 percent to 20 percent water while the rest of the body is closer to 70 percent or 80 percent water.
The simplest body analysis scale allows the user to enter information such as gender and activity level. A person stands on the scale and the scale measures both weight and impedance of the current as it travels up one leg through the body and down the other leg. A microprocessor uses a formula to give an estimate of body fat. More elaborate body analysis scales found in hospitals or health clubs allow a user to enter detailed information such as age and specific fitness level information. These scales can give readouts that include fat weight, body mass index, and hydration levels.
A body analysis scale measures body fat accurately to within 5 percent. For home users, the scales are better used to track changes in body fat over time. The conditions for using the scale need to be fairly consistent for the most accuracy. Body temperature and hydration level should be approximately the same for each use, and weighing should take place around the same time of day.