Body Composition Measurement Tools

When people begin exercising often the reason they give as to why they are starting is “to lose some weight”.  The truth is – they don’t want to lose weight – they want to lose fat.  This is often why only looking at a scale is not the best indicator of fat loss, as an athlete can lose fat, gain muscle and be the same weight.

Why Body Composition is Important

Fat stores can be a useful source of energy – but as a special operation candidate preparing for selection we want you to be only carrying around weight that will help you get from point A to point B.  Losing 10 pounds of fat prior to selection can be as helpful as taking off a 10# weight vest before doing the thousands of pushups and pullups coming your way.  This should not be taken to the extreme, as your body will suffer should your fat stores drop too low.

Body composition is typically referred to in body fat percentage.  This is the amount of body weight that is fat vs. the amount that is fat free mass (FFM).  Below are a list of ways to measure body composition in a list from the most valid and reliable to the least.  Before doing so we must first define validity and reliability.

Validity: Does the test actually measure what it is supposed to?

Reliability:  How consistently does this measure what it is supposed to?

Dual-Energy X-Ray Absorptiometry (DEXA) Scan

A DEXA scan is like an x-ray that uses two different levels of radiation.  One only is absorbed by the denser body parts such as muscle and bone, and the other level of radiation is only absorbed by soft tissues (skin, fat).  Knowing an athlete’s weight, volume of FFM, fat mass, and the density of fat, muscle and bone a DEXA scan can tell you what the athlete’s body fat percentage is.   This is the gold standard for body composition testing.  However, at risk populations such as pregnant women are unable to use this test due to the x-rays.

Hydrostatic Body Fat Testing

This method of testing your body fat is by far the most uncomfortable to participate in.  In this test the athlete is submerged in a water tank and expels all of the air in their lungs while they are weighed underwater.  As fat floats in water a body with more fat will weigh less underwater. The body’s volume is measured by measuring water displacement. Then, by weighing the body in and out of water the athlete’s body composition can be determined.  Although this test is valid and reliable it is a more lengthy test and if the athlete does not expel all of the air in their lungs then the results can be skewed.

Bod Pod (Air Displacement Plethysmograph)

The bod pod test uses air displacement to determine the athlete’s volume and uses air density to calculate body composition.  The athlete sits inside of a sealed chamber while they are weighed and measured by the machine.  The benefits of the bod pod are that they are a quick and idiot proof method of calculating body composition without large risk of user error.  The issue with these pods is that they are very susceptible to changes in air flow in the testing room.  This means that a draft in a room could skew the results.  In saying that, when performed correctly a bod pod is a convenient and accurate method of measuring body composition.

Calipers (Skinfold)

There are a variety of skinfold tests, varying from 3-8 site tests.  This test is conducted by pinching a part of the body, so that the subcutaneous fat can be measured in millimeters (mm) using a caliper.  The amount of mm is then totaled and used in some complicated formulas – there are LOTS of different ones – to give you a body fat percentage.  This type of testing is great because it is inexpensive, relatively fast and can be performed on any population.

The issues with this test is that there is a large variance in user error with the calipers.  A lot of landmarks for skinfold testing is eyeballed or based on landmarks.  Expert kinanthropometrists are extremely reliable and masters of their craft.

Calipers are often referred to as a perfectly imperfect system.  With repetition practitioners become fairly reliable.  However, the differences between practitioners is usually where issues come up as each practitioner will have slightly different landmarks and different skinfold pinching technique.  If the same athlete is tested by the same practitioner it can be a good way of measuring progress, switching between practitioners is where issues with reliability come in.

BioElectrical Impedance (Ex: InBody Scanner)

These tests use a small electrical impulse that is sent through your body and based on the density of the tissue that the impulse travels through the body at different speeds.  Bioelectrical impedance is typically not a reliable method of measuring body fat percentage.  The reason for this is because hydration levels can have a major impact on how the electricity passes through the body.  In saying that, if hydration and time of day is a controlled factor then bioelectrical impedance can be a good option.  Also, not all bioelectrical impedance tests are created equal.  An InBody Scanner that has several connection points are able to give results regarding the body composition of individual limbs, which can be helpful for determining muscular imbalances.

Tape Measure and Body Mass Index (BMI)

The largest sets of data are typically using BMI or waist circumference because they are cheap and easy to test large groups of people in a short amount of time.  The downside of this is that these tests account for 80% of the population within the norm but do not account for the outliers – such as athletes.

For example: Rich Froning is 5’9 (1.75cm) and around 200lbs (89.3kg).  He has a BMI 29.2, bordering on obese.  Clearly, looking at Rich Froning, the BMI does not tell an accurate story of his body composition.

Waist circumference has been shown to be a fairly accurate way of predicting health issues.  However, this again does not account for the outliers and athletic populations.  These methods of body composition measurements should be restricted to those falling within the general population category.

body mass index

Key Points:

  • Most often, leaner is better. Be mindful of potential performance decreases after dropping under 12% bodyfat (for men).
  • DEXA Scans and Hydrostatic Weighing are the gold standards
  • Bod Pods, Skinfold and BioElectrical Impedance have issues but can be used
  • BMI and Waist Circumference measurements are best used for large studies with the general population