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?