Body Fat Test: One Year Later (part 1)

by | Jan 30, 2009

This week my awesome gym (Bakar Fitness) was once again offering hydrostatic body fat testing courtesy of Fitness Wave.

I had my body fat and metabolic rate tested last year and thought it would be interesting and informative to go in for a one year follow up.

I also want to give you an idea of what to expect if you decide to “get dunked.”

(note: This is part 1 of a 2 part post. The first post focuses on the hydrostatic testing experience rather than my personal story. Come back next week for part 2).

“Hydrostatic” body fat testing is a lot like it sounds: you get weighed under water. The principle behind the method is that virtually all tissues in your body–bones, muscles, organs–weigh more than water. That is, everything sinks except fat. The density of fat is lower than other tissues and consequently, fat weighs less.

Using this knowledge you can calculate how much fat you have by comparing your weight inside and out of the water. The lighter you weigh under water compared to on land, the more fat you have. You can convert this into an exact body fat percentage by doing a little math. (Don’t worry, Fitness Wave does this all for you).

Calculations are even more accurate when you throw in measurements like height. For this test I even had my ankle size measured.

During the test you step into a tank of warm water (pictured to the right) and position yourself on a metal scale. You are instructed to blow out all the air from your lungs and submerge your head while the operator checks your weight. This process is repeated at least three times, and takes about five minutes.

The bottom line is that when packing your bag for your body fat test remember that you will get wet.

A bathing suit and towel are appropriate.

If it is January (or summer in San Francisco), you may also want to bring a change of warm clothes and sandals. When testing, the Fitness Wave trailer is stationed down near the loading docks between the Community Center and Genentech Hall at UCSF Mission Bay. You probably don’t want to walk from the locker room to the trailer in your bikini.

Hydrostatic Testing Checklist:

  1. Bathing suit
  2. Towel
  3. Warm clothes
  4. Convenient shoes
  5. Healthy dose of perspective

Packing your bag is not all the planning you need to do before getting a body fat test. As I explained last year, I also recommend you decide before you go about what you will do with this personal information. Determine beforehand whether or not you want to tell your friends what you are made of to save yourself from stress and awkward conversations later on.

Overall the testing was (once again) a great experience, and I highly recommend getting a hydrostatic test if you get the opportunity. I received a print out of my numbers and an email with more information the next day.

Next time I will reflect upon how my eating and workout habits have affected my body composition over the last year. Check back next week for all the gossip.

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Click here to read Body Fat Test: One Year Later (part 2)

Have you ever had your body fat tested? Are you interested?

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11 Responses to “Body Fat Test: One Year Later (part 1)”

  1. Anonymous says:

    This anticipation is killing me. Tell us your bodyfat %!!!!!!!!!!!!!

  2. Travis Saunders, MSc says:

    I’ve done the under water weighing myself, blowing out all the air then holding my breath underwater was intense! One problem with under water weighing is that there is always some air left in your lungs, intestines, etc, and the density of fat tissue differs between races, which can screw up the calculations a bit. Still a very cool test though, and far more affordable than alternatives like DEXA or MRI.

  3. Matt Shook says:

    I’ve heard of this but never tried it myself. I have no idea what my body fat % is. Looks kind of fun…

  4. Darya Pino says:

    @anonPatience is a virtue! =D—–@TravisGreat point, I forgot to mention lung emptying. The exhale was only for a brief while, and it was actually a fun challenge to get all those bubbles out.I imagine excess air in the body would probably only slightly inflate the number. For most of us, it is probably better to hear a number slightly too high than slightly too low. (For those of you who are confused, air would increase your buoyancy and make it appear like you had more body fat than you do). I would have more of a problem with statistical error in the other direction, giving people a false sense of security in their fat level. The goal should be to get an estimate of true body fat, not to brag to your friends.—–@MattIt was pretty fun! You should take the opportunity if you ever get it 🙂

  5. Scott says:

    Interesting that you guys mention about the affect of air in the lungs and what that would do to the estimate. I would think that the machines algorithms for calculating body fat would assume that the lungs are emptyed; they could just as easily estimate the average lung capacity and not make you empty your lungs, but it of course would be less accurate- and I disagree that it is better to have a body fat % that is a little higher than the true percentage. The whole point of going and spending all that money is so you can find your EXACT percentage, not one that is a little high that is supposed to inspire you to lose weight/fat. The truth is, even when you fully exhale there is still ‘deadspace’ in your respiratory airways that will make you more boutant, thus overestimating your body fat %. I wonder how much the respiratoy deadspace contributes to the discrepancy. So, whoever has actually had their body fat tested, can take solace that thier actual percentage is probably even a little less than what is reported to you by the company.

  6. Anonymous says:

    Lousy, no good body fat.

  7. Darya Pino says:

    @ScottI just hope no one spends too much time worrying about this stuff. Better to spend time buying and cooking vegetables if you actually care about your health. Numbers can only help you so much. When it comes down to it, eat right and you will be health and thin.—–@AnonIndeed 😉

  8. NB says:

    I’ve never been tested, but I am kind of interested in one of the home scale-resistance body fat testers; obviously not the gold standard, but at least you could measure it weekly for instance and have a much better short term gauge- far more useful than weight. My question is when are they going to overhaul the BMI (which I compare to the FDAs old food pyramid, faulty on multiple levels) with a new index based on body fat percentage. I guess its just another stepping stone…..

  9. Mike says:

    Yeah, I had my body fat % test. Results were 0%. I guess I’m just pure muscle and brains…..

  10. Karen says:

    I’ve heard about this kind of body fat testing, but have never seen a truck like this anwhere or know where to find one. Part of my issue is that I know I can be in better shape just by stepping on the scale, do I really need to get my % measured?

  11. Darya Pino says:

    @NB @KarenI think there is good reason for getting an accurate reading of body fat. For one thing it makes it very clear to you how you are doing on nutrition and exercise. You may know you want to lose weight, but your body fat percentage can tell you if you are working out effectively and your diet is all that needs tweaking, or if you should be getting to the gym more regularly. —-@MikeYou know, brains are made of fat. I’m just saying…

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