Employee Wellness Programs Glossary Term:
"What Is Underwater Weighing?"

Underwater weighing is also known as hydrostatic weighing. Underwater weighing, as the name suggests, is weighing a human underwater. This method is popularly used for weighing the human body. Underwater weighing is used to determine the body composition or the different components that constitute a person's total body density. The body composition is calculated using Archimedes principle of displacement.

Underwater weighing is considered to the most accurate standard to assess body composition. Underwater weighing is based on the principle that the density of fat-free and fat mass of human body are constant, lean tissues in human body such as muscles and bone have greater density than water, fat tissues in the human body have less density than water. Therefore, when a person is weighed underwater, a person who has greater body fat will weigh less. On the other hand, a person with more muscles will weigh less underwater.

Underwater weighing involves a particular procedure. The procedure ensure the body mass is assesses precisely. Before underwater weighing is performed, the person is first weighed on land. Then the person is immersed into a large water tank while the person is seated on a special scale. The scale is lowered slower underwater and the person is instructed to expel air from his lungs and remain still while underwater weight reading is noted down. The same procedure is repeated 3 times and the average underwater weight is calculated. Once the average body weight is calculated, a special calculation is used to determine fat weight and lean weight to determine the person's exact percentage of body fat.

One of the most significant advantages of underwater weighing is that the body density assessment done through this method is considered to be the gold standard. The results obtained can be used for other indirect measures.

However, underwater weighing also has few disadvantages. A major drawback is that the equipments used for underwater weighing is expensive. The water tanks used for weighing are not easily available; the tanks are located in universities and research institutes and are not accessible for common people.

Though underwater weighing is a popular method to measure body mass composition, many researchers have apprehensions about the validity of the weighing method. Researches suggest that underwater weighing may underestimate the body fat percentage of athletes who tend to have more dense muscles as compare to non-athletes. Researchers have also suggested that underwater weighing may also overestimate the percentage of body fat in elderly people who may suffer from osteoporosis.

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