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The method that uses electrical signals to assess body composition is bioelectrical impedance analysis (BIA). This technique works on the principle that different tissues in the body conduct electricity at different rates. Muscle, which contains a high percentage of water, conducts electrical signals well, while fat, which contains less water, resists the flow of electricity.

During a BIA measurement, electrodes are placed on the skin, typically on the hands and feet. A low-level electrical current is passed through the body, and the resistance to the current is measured. This data is then used to estimate total body water, lean mass, and fat mass, providing a comprehensive picture of body composition.

In comparison, hydrostatic weighing involves measuring body density by submerging an individual in water, while skinfold thickness measurements involve using calipers to measure fat near the skin's surface at specific sites on the body. Ultrasound scanning uses sound waves to visualize tissues and can provide measurements related to muscle and fat but not through electrical signals like BIA. Each of these methods has its own advantages and limitations, but BIA is specifically distinguished by its reliance on electrical signal conductivity to assess body composition.