Strength and physique athletes share a common interest in body composition. Measuring body composition can help you determine if a training program or diet has been effective, what a reasonable weight class might be, and if your contest prep is on the right track. If you look into getting your body composition tested, you’ll notice that there are a ton of different ways to measure it. But how are the methods different, and which methods are accurate?


Methods for Measuring Body Composition

The most accurate way to measure body composition is by cadaver dissection. Most people aren’t that desperate to obtain some numbers, so scientists have developed methods to estimate body composition. When discussing these methods, the terms “validity” and “reliability” come up frequently. Validity refers to how well a method gives us a “true” value. So cadaver analysis is certainly the most valid method, but we can assess the validity of a particular method by comparing it to another method that is validated. Reliability refers to how consistent a method is when repeated.

Think about the classic example of throwing darts at a dart board. Validity means you hit the bull’s eye. Reliability means you hit the same spot repeatedly, but this spot may not necessarily be near the bull’s eye. Something that is reliable can still be used to track changes, even if the number it gives you isn’t exactly a “true” value.

Validity Figure


Underwater Weighing (UWW)/Hydrostatic Weighing

This method was developed way back in the 1940s, and uses the Archimedes principle to determine body density, which is used to estimate relative amounts of fat mass and fat-free mass using various equations. It’s common to call UWW the “gold standard” for measuring body composition, which can sometimes cause people to overestimate its validity. This method was the first to gain widespread acceptance, and it is the measurement by which subsequent techniques were typically compared. But that doesn’t mean its validity is perfect. Some research has suggested that UWW can be off by up to ±4 percentage points when used to estimate body fat percentage (BF%) [5]. Despite being considered the “gold standard” measurement, this value still relies on a number of assumptions, and can be influenced by hydration, ethnicity, age, sex, training status, and which equation is selected for calculation. This method can also be unpleasant for the subject, and tedious for the tester. Nonetheless, it is a fairly reliable method that can be used to track changes when performed properly.

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