Which method for assessing body composition is very accurate but expensive and uses water displacement?

Which method for assessing body composition is very accurate but expensive and uses water displacement?

• A. BMI
• B. Hydrostatic weighing
• C. Skinfolds
• D. Bioelectrical impedance analysis

Answer: (B)

Measuring body composition by determining body density through water immersion uses Archimedes’ principle: the amount of water displaced equals the body's volume. By weighing a person in air and then underwater, you obtain their body volume. With the body’s total mass known, you calculate body density. From that density, a two‑component model separates fat mass from fat‑free mass, and a conversion equation (often the Siri equation) yields percent body fat. This method is highly accurate because it directly measures volume and relies on well‑established density relationships rather than relying on estimates of hydration or fat distribution. The trade‑off is practicality: it requires specialized equipment like a hydrostatic tank and precise scales, trained staff, and submersion of the person, which makes it expensive and less convenient for routine use.

Measuring body composition by determining body density through water immersion uses Archimedes’ principle: the amount of water displaced equals the body's volume. By weighing a person in air and then underwater, you obtain their body volume. With the body’s total mass known, you calculate body density. From that density, a two‑component model separates fat mass from fat‑free mass, and a conversion equation (often the Siri equation) yields percent body fat. This method is highly accurate because it directly measures volume and relies on well‑established density relationships rather than relying on estimates of hydration or fat distribution. The trade‑off is practicality: it requires specialized equipment like a hydrostatic tank and precise scales, trained staff, and submersion of the person, which makes it expensive and less convenient for routine use.