Body Fat %

Today I wanted to write a little about body fat percentages.  More specifically, how we can figure them out.

There is only one way to determine exactly how much body fat we have.  It involves grinding you up until you are a liquid, like in a giant blender.  We then wait for the goo to settle and determine how much fat is there compared to the rest because the fat will rise to the top of the mixture.  Anybody interested?

Of course not.  So what we have left are ways to estimate body fat percentages.  This is not as accurate as the true measurements, but it’s all we got!  From here I’ll rank my favorite methods of estimating body fat percentage.

The best is a procedure called DEXA (dual energy x-ray absorptiometry) which used a giant x-ray machine from both sides to determine your body density which is used to figure out body fat by subtracting lean body mass and bone mass from total mass.  The results are comparable to underwater weighing (the current gold standard) but it is very expensive.  Personally I think I’d rather save a few bucks than lose a few percentage error points.

Expensive but accurate

Next we move on to underwater weighing.  This involves more expensive equipment, and results skewed largely due to participant adhesion to the procedure.  It involves being submersed in a water tank and blowing out all of your air.  And I mean all of your air, a very difficult thing to do.  For even less error you need to have your lung capacity measured to account for the air that stays in your lungs no matter how hard and long you exhale.  Any extra air can skew the results.

Google search turned up the old tank at FAU I used to use...

Again, this test measures body density and estimates body fat percentage with great accuracy.  But it is another expensive test involving college lab equipment and a high level of error based on each individual.  Again, I’d rather save my money and accept the level of error associated with other tests.

The most applicable test is the skin fold test.  A good tester can get close to the accuracy of the underwater weighing tank or the DEXA machine, but that is dealing with very experienced professionals that do the test multiple times daily.  An average test produced a decent amount of error.  The nice part about this test is that it is inexpensive and quick to perform.  It involves a series of pinches and measurements of said pinches in specific locations on the body.  These fold measurements are used in an equation factoring in gender, age, and weight to produce an estimate of body density and then body fat percentage from there.  From my experiences in school and my old employer I like to consider myself an above average tester so this is the test we use when requested at Coastal Performance.  This test provides the best balance of accuracy and is not very demanding on the participant.

Should be on an angle, not horizontal... but still, good overall test

The last test is my least favorite and the most common.  That is the bioelectrical impedance method involving a device that sends an electrical shock (you can’t feel it) through the body and bases its body fat estimate on the speed at which the electricity travels.  This test is highly inaccurate and can fluctuate drastically throughout the day.  I would stay away from any tests involving this test as it can change in 10 minutes, leaving you clueless when you check back to it in a couple months.

Please don't use this or believe anyone that says it's good enough.

So for tests I recommend the skin fold test, but have it done by a competent practitioner.  A great test has 3% error in either direction so take it for what it is, an estimate.  But if you use the same tester, we can pick up differences.  For example if you start at 25% body fat on the skin fold test.  That means you’re really anywhere from 22%-28%.  2 Months later you’re at 22%.  This means we’re really anywhere from 19%-25%.  We can’t say it with 100% accuracy, but it’s safe to assume that this shows us a decrease in body fat percentage, most likely of around 3%.  Again, not perfect, not guaranteed, but it’s a great way to keep track of your progress in the gym.



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Filed under Fat Loss, Training

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