Compare DEXA

There are a lot of other methods available currently to measure body composition, some are ok, and some are not so good, let’s clear up some of the confusion and compare the methods.

What is Hydrostatic Weighing?

Hydrostatic also known as underwater weighing is a technique in which an underwater tank is used to calculate a person’s body fat percentage and lean mass total.

How it works:

Your land weight it taken and recorded. You are then lowered into the tank and asked to exhale all air from your lungs. Your weight underwater is then recorded by the technician using a set of scales in the tank. Your body fat percentage is then calculated by comparing the two weights. The procedure is then repeated 5 times to get an average reading and improve accuracy.


  • Has been used for many years, good subject data exists as a result of research done.


  • Expensive
  • Skilled and experienced operator is needed to complete tests accurately
  • Need to be fully submerged in water in bathing suit which is uncomfortable for many clients

Bioelectrical Impedance Scanning

You may have a set of these scales at home or seen them in a gym before.

BIA involves running a light electrical current through your body. Fat-free mass contains mostly water, while fat contains very little water. Thus, fat-free mass will have less resistance to an electrical current. By determining the resistance of a current running through your body, theoretically we could get an estimate of how much fat-free and fat mass you have. There are many BIA devices out there, including devices by Omron and Tanita.

While the theory behind BIA sounds nice, it is problematic. First, an electrical current will follow the path of least resistance through your body. This means that, if you carry a large amount of fat underneath your skin, the BIA won’t even hit it; the current will instead pass through internal tissues.

The biggest problem with BIA is that it’s a prediction based off of a prediction. When a manufacturer develops a BIA device, the manufacturer gathers a large group of people and determines their body composition using another method. Usually, this method is not the gold standard of the 4-compartment model; most often it is hydrostatic weighing. The manufacturer then takes the results of the BIA equipment, and develops a prediction equation from those results (and variables like the individual’s height, weight, and gender). This equation is designed to predict what your body fat would be if we were to perform underwater weighing on you, based on the BIA results.


  • Cheap, Anyone can perform this type of scan regardless of qualification


  • Inaccurate, poor reliability and repeat-ability, invasive with electrodes required for some devices


Skin Folds

Calipers measure subcutaneous fat, or fat located directly under your skin, by lightly pinching fat folds at different body sites.

Skin-fold measurements are converted into a percentage, which can be compared to various norms, and improvements in diet and/or training intensity can subsequently be made to further strip body-fat, to meet physical objectives.

Although a good way in which to chart progress, it should be said that calipers cannot be totally accurate.

There are many sources of error with this technique.  First, the technique is highly sensitive to how skilled the technician is at grabbing the fat and pulling it away from the underlying muscle tissue.  Improper technique can introduce error into the results

Another source of error is in the equation used to predict body density.  Any equation is only valid when testing people similar to the people used to develop the equation in the first place.  Various factors including the density of fat-free mass can change depending upon your race. It is critical that, if you do use skinfolds for body fat estimation, you use an equation that was specifically developed for your race, age, and gender.



The human body is very complex! There are things going in, coming out, transforming, and dissolving all of the time. As a result, your weight can fluctuate wildly over the course of a 24-48 hour period.  Depending on what you ate today, how much water you drank, if there was sodium in your food, what kind of clothing you were wearing, what time of day you weigh yourself, your weight will change.

While your weight is important, what’s even more important is how much muscle you have. Muscle takes up less space than fat, making you look slimmer, and it’s more metabolically active. When you exercise, you gain muscle, raise your metabolism and lose fat, but that fat loss won’t always show up on the scale. Where it will show up is on a DEXA scan, and you will see the difference in how your clothes fit and how your body looks. All that can happen even if the scale isn’t moving.


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