The test administrator records the weight when no more air bubbles appear in the water and the individual can then resurface. The test is typically repeated several times and the average of the weights used to minimize errors. The recorded weight will be plugged into equations that account for any leftover air in the lungs and gastrointestinal tract to calculate body density in water and total body fat percentage.

Underwater weighing is considered one of the most accurate forms of measuring body composition. Underwater weighing was once considered the "gold standard" for comparing accuracy and reliability of other body composition measurement methods.

However, with newer technologies available, it's being used less often since it does require special equipment. The individual should also be capable and comfortable expelling air from their lungs and keeping still while submerged underwater.

Underwater weighing is one method for calculating percentages of body fat and lean mass. Although highly accurate, it is not widely available, and therefore, may not be convenient for taking regular weight measurements.

Other methods, such as bioelectrical impedance or skinfold measurements, may be more convenient for tracking changes in weight and body composition. Ana Reisdorf, MS, RD is a freelance health writer and dietitian with 12 years of experience in the field of nutrition.

You can learn more about her at anareisdorf. Body Fat Testing Through Underwater Weighing 2 Minutes Read. Underwater weighing is a traditional and reliable method of measuring body composition. Underwater Weighing Underwater weighing, also known as hydrostatic weighing, is a method of calculating body fat percentage based off body density.

The person must remain motionless underwater while the underwater weight is recorded. This procedure is repeated several times to get a dependable underwater weight measure. See videos about Hydrostatic Weighing.

For more accuracy residual lung volume RV should be physically measured, though there are calculations for RV estimation. One estimation of residual volume is one third of forced vital capacity FVC. See lung function tests. advantages: Underwater weighing is the most widely used test of body density and in the past was the criterion measure for other indirect measures.

disadvantages: The equipment required to do underwater weighing is expensive. The tanks are mostly located at university or other research institutions, and there is generally not easy access for the general population.

validity: This method may underestimate body fat percentage of athletes as they tend to have denser bones and muscles than non-athletes, and may overestimate body fat percentage of elderly patients suffering from osteoporosis. comments: The water temperature is often elevated to provide a comfortable experience for the subject, however the density of water is dependent on the temperature and should be factored into the equation.

We have over fitness tests listed, so it's not easy to choose the best one to use. You should consider the validity, reliability, costs and ease of use for each test.

Use our testing guide to conducting, recording, and interpreting fitness tests. Residual volume can be measured by gas dilution procedures or estimated from a person's age and height: [3]. It is worth noting that these estimates are for adults aged , have standard deviation of about 0.

The most commonly used equations for estimating the percent of body fat from density are those of Siri [6] and Brozek et al. Contents move to sidebar hide. Article Talk.

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Download as PDF Printable version. In other projects. Wikimedia Commons. Technique for measuring the density of a living person's body.

Participant must wear swim suits. However, as it is mostly only available in research laboratories or university settings, it is generally used for research purposes and not applicable in clinical practice or in large-scale population studies.

It is used less frequently since the introduction of air displacement plethysmography as this technique is better tolerated by participants. Figure 1 Illustration of measurement of underwater body weight.

The most commonly used equations for estimating the percent of body fat from density are as follows:. Considerations relating to the use of hydrostatic underwater weighing for anthropometry in specific populations are described in Table 2.

Refer to section: practical considerations for objective anthropometry. About About the DAPA Measurement Toolkit What's New Other resources Toolkit Team Contact.

Introduction Validity Reliability Error and bias Feasibility Data processing Statistical assessment of reliability and validity Harmonisation.

Introduction Subjective methods Objective methods Harmonisation Videos Dietary assessment decision matrix. Introduction Subjective methods Objective methods Harmonisation Videos Physical activity assessment decision matrix.

Introduction Subjective methods Objective methods Anthropometric indices Harmonisation Videos Anthropometry decision matrix. Anthropometry Domain. Hydrostatic underwater weighing. What is assessed? How is the measurement conducted? When is this method used? How are estimates of body composition derived?

Strengths and limitations Populations Further considerations Resources required Instrument library References. Two methods to determine total body water An allowance must be made for residual lung volume the air that remains in the lungs after a maximal exhalation as this air increases the participant's buoyancy.

Dry bodyweight After having measured or estimated residual lung volume, the participant's dry weight is measured wearing a swimming suit or running shorts. Underwater weight The participant climbs into the underwater weighing tank and sits in a seat that hangs from a force load-cell.

After the underwater weight stabilizes approximately 5 seconds , the participant is instructed, though yelling or pounding on the side of the tank, to return to an upright position.

During weighing, the participant is always free to stand up or return to the upright position. Several trials may be required before the participant becomes accustomed to the procedure and consistent readings recorded.

Four to eight trials are usually performed. The depth of the water is approximately cm, and temperature maintained between 30 and 34 C. The density of water is dependent on the temperature and should always be factored into the equation.

After each testing session, the water is drained and the tank allowed to dry. Pre-test Guidelines Participants must not eat or engage in strenuous exercise for at least 4 hours before their scheduled appointment. Body density is required to calculate percentage body fat.

Strengths and limitations. An overview of the characteristics of hydrostatic underwater weighing is outlined in Table 1. elderly Participant must be able to perform complete air exhalation There is a possibility of considerable error introduced by the miscalculation of residual volume RV The test does not identify the exact parts of the body where the fat is located e.

unable to assess fat distribution The accuracy of body density measurements can be affected by the consumption of food and carbonated beverages shortly before the test, fluid loss during intensive exercise, fluid retention during menstruation, and the degree of forcible exhalation while submerged Like all the 2 component model methods, it assumes when calculating total body density that the relative amounts and densities of bone, muscle, and water comprising the fat-free mass are essentially the same for all individuals, regardless of age, sex, ethnicity or fitness level Table 1 Characteristics of hydrostatic underwater weighing.

Consideration Comment Number of participants Small Relative cost Medium Participant burden High Researcher burden of data collection High Researcher burden of coding and data analysis Low Risk of reactivity bias No Risk of recall bias No Risk of social desirability bias No Risk of observer bias No Space required High Availability Medium Suitability for field use No Participant literacy required No Cognitively demanding No.

Table 2 Anthrompometry by hydrostatic underwater weighing in different populations. Population Comment Pregnancy Suitable but unable to disentangle the mother-fetal unit Infancy and lactation Not suitable Toddlers and young children Not suitable Adolescents Not suitable Older adults May not be suitable as older individuals have less dense bones, resulting in over-estimation of body fat Ethnic groups Suitable Other athletes Athletes tend to have denser bone and muscle tissue, resulting in under-estimation of body fat Other obesity Suitable.

However, the accuracy depends on the skill of the person performing the assessment. Body shape varies from person to person, and the shape of your body provides information about your body fat 4.

For men, the circumferences of the neck and waist are used in this equation. For women, the circumference of the hips is also included 5. Using body circumferences to estimate body fat is quick and easy. However, the accuracy of this method can vary widely and is not considered an ideal method of measuring body fat percentage.

As the name implies, DXA uses X-rays of two different energies to estimate your body fat percentage 6. During a DXA scan, you lie on your back for approximately 10 minutes while an X-ray scans over you. The amount of radiation from a DXA scan is very low. DXA is also used to assess bone density and provides detailed information about the bone, lean mass and fat in separate body regions arms, legs and torso 8.

DXA is more accurate than many other methods of assessing body fat percentage. This method, also known as underwater weighing or hydrodensitometry, estimates your body composition based on its density 9.

This technique weighs you while submerged under water after exhaling as much air as possible from your lungs. You are also weighed while you are on dry land, and the amount of air left in your lungs after you exhale is estimated or measured.

All of this information is entered into equations to determine the density of your body. Hydrostatic weighing is an accurate way to assess your body fat.

Similar to hydrostatic weighing, air displacement plethysmography ADP estimates your body fat percentage based on the density of your body 9. However, ADP uses air instead of water. The relationship between the volume and pressure of air allows this device to predict the density of your body You sit inside an egg-shaped chamber for several minutes while the pressure of the air inside the chamber is altered.

To obtain accurate measurements, you need to wear skin-tight clothing or a bathing suit during testing. The Bod Pod is the main ADP device currently used.

It predicts your body fat with air rather than water. BIA devices detect how your body responds to small electrical currents. This is done by placing electrodes on your skin. Some electrodes send currents into your body, while others receive the signal after it has passed through your body tissues.

Electrical currents move through muscle easier than fat due to the higher water content of muscle BIA devices work by sending small electrical currents through your body to see how easily they travel through your tissues. Many different devices are available, although advanced devices produce more accurate results.

BIS and BIA devices look similar but use different technology. BIS uses a much larger number of electrical currents than BIA, in addition to high and low frequencies, to mathematically predict your amount of body fluid BIS also analyzes the information differently, and some researchers believe that BIS is more accurate than BIA 14 , However, similar to BIA, BIS uses the body fluid information it gathers to predict your body composition based on equations The accuracy of both of these methods depends on how similar you are to the people for whom these equations were developed However, BIS uses more electrical currents and processes the information differently.

However, while BIA and BIS send currents through your whole body, EIM sends currents through smaller regions of your body These devices are placed on different parts of the body to estimate the body fat of those specific areas Because this device is placed directly on specific body regions, it has some similarities to skinfold calipers, although the technologies are very different.

EIM injects electrical currents into small body regions. Portable devices are placed directly on different body parts to estimate the body fat percentage at those locations. More research is needed to establish the accuracy of this method.

For some devices, you stand on a rotating platform for several minutes while the sensors detect your body shape. Other devices use sensors that rotate around your body.

In this way, 3-D body scanners are similar to circumference measurements. However, a greater amount of information is provided by a 3-D scanner The method uses information about your body shape to predict your body fat percentage. More information is needed about the accuracy of these methods.

Multi-compartment models are considered to be the most accurate method of body composition assessment 3 , These models split the body into three or more parts. The most common assessments are called 3-compartment and 4-compartment models. These models require multiple tests to get estimates of body mass, body volume, body water and bone content For example, hydrostatic weighing or ADP can provide body volume, BIS or BIA can provide body water and DXA can measure bone content.

Information from each of these methods is combined to build a more complete picture of the body and obtain the most accurate body fat percentage 21 , However, they involve multiple tests and are not typically available to the general public. Some methods, such as skinfold measurements, circumference calculations and portable BIA devices, are inexpensive and allow you to be measured in your own home as frequently as you like.

The devices can also be purchased online easily, such as on Amazon. Most of the methods with highest accuracies are not available to use in your own home. If you want a more accurate assessment and are willing to pay for it, you could pursue a method with good accuracy like hydrostatic weighing, ADP or DXA.

Ideally, you should do the test before you have anything to drink, especially for methods that rely on electrical signals like BIA, BIS and EIM. Assessing yourself the same way each time will reduce error rates and make it easier to tell if you are making progress.

However, you should always interpret your results from any method with caution. Even the best methods are not perfect and only give you an estimate of your true body fat.

One estimation of residual volume is one third of forced vital capacity FVC. See lung function tests. advantages: Underwater weighing is the most widely used test of body density and in the past was the criterion measure for other indirect measures.

disadvantages: The equipment required to do underwater weighing is expensive. The tanks are mostly located at university or other research institutions, and there is generally not easy access for the general population. validity: This method may underestimate body fat percentage of athletes as they tend to have denser bones and muscles than non-athletes, and may overestimate body fat percentage of elderly patients suffering from osteoporosis.

comments: The water temperature is often elevated to provide a comfortable experience for the subject, however the density of water is dependent on the temperature and should be factored into the equation. We have over fitness tests listed, so it's not easy to choose the best one to use.

You should consider the validity, reliability, costs and ease of use for each test. Use our testing guide to conducting, recording, and interpreting fitness tests. Any questions, please ask or search for your answer. To keep up with the latest in sport science and this website, subscribe to our newsletter.

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Hydrostatic Weighing. Any comments, suggestions, or corrections? Please let us know. Search This Site. Skinfold caliper testing is one of the simplest ways to measure body fat. There are several variations to the test, but often a three-site or seven-site test is used. During the test, a test administrator uses a pair of calipers to measure the thickness of skin folds and the fat underneath at three or seven different locations on the body.

Skinfold tests can be accurate to about 3 to 4 percent for 70 percent of the population, but they can be significantly less accurate when administered by somebody inexperienced.

Bioelectrical impedance analysis is a common feature on bathroom scales. It uses a small electrical current to estimate body fat based on how easily the current moves through the body. Fat is a poor conductor of electricity, so more resistance indicates a higher body fat percentage.

The accuracy of these scales can vary depending on the brand. Your level of hydration can also significantly change the results because water conducts electricity easily. Commercially available scales are generally less accurate than hydrostatic weighing and other medical research tools, but they can provide you with a rough estimate of your body composition.

DEXA uses X-rays to measure body fat, muscle mass, and bone mineral density. Some companies offer DEXA scans for about the same price or slightly more than hydrostatic weighing. MRI and CT scans are the most accurate methods of measuring body fat. However, these imaging tests are usually limited to medical research and are very expensive.

The machines that perform MRI or CT scans work by taking multiple cross-section images of your body. A trained technician can identify various types of tissues, such as bone, muscle, or fat, in these images.

Hydrostatic weighing tests are available at some universities, medical research centers, and fitness centers. If you want to get tested, you can try contacting universities or colleges in your area that have kinesiology or exercise science programs. You can also search for gyms or fitness centers in your area that may offer the test.

Some companies also offer mobile hydrostatic testing. This involves driving the hydrostatic tank to your location. An administrator will calculate your body fat percentage by comparing your land weight with your underwater weight.

This method of measuring body fat is most commonly used in research and with athletes, but some gyms and universities in your area may offer testing for a fee. Consistency is the key to accurate weight measurement. Choose a time of day and always weigh yourself at that time.

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What Is Hydrostatic Weighing? Medically reviewed by Jake Tipane, CPT — By Daniel Yetman on August 10, How hydrostatic underwater weighing is done. Advantages of underwater weighing.