Hydrostatic weighing is a tedious method of measuring bodyfat but is by far the most accurate method. The first part of the test consists of some spirometric measurements (spirometry). Essentially you breathe into this tube and exhale everything you have in your lungs. You do this about three times until you see stars and are ready to pass out. The purpose of this is to measure the capacity of your lungs and to calculate from that how much residual air is still in your lungs even after you think you have breathed everything out. Then you get into your swimming suit and get into the tank. It is basically a big person-sized vertical drum filled with lukewarm water. You sit in this little chair which is suspended from the ceiling. When the test starts, you breathe everything out again and the chair is lowered into the water. Your entire body is submerged. You have to hold your breath (you don't really have any air left so this is not very long) and try to keep from moving around. I think they figure out how much you weigh in the water and calculate the buoyancy from the residual air and then compare that to your weight outside of the tank and somehow come up with an accurate measurement of bodyfat.
Looking back to March 7th, 1994 (age 21) I was getting ready for a competition and wanted to know exactly how much bodyfat I had. I took the test and it came back with the following results:
Weight: 180.2 lbs.
Bodyfat Percentage: 8.795
Lean Body Mass: 164.351 lbs.
Weight of Bodyfat: 15.849 lbs.
Now I find this very interesting in comparison to my recent body composition test as my lean body mass has apparently increased by almost 6 lbs. in the last 10 years. In fact, on March 7th of this year, it will be 10 years to the day since the last test. This is what I looked like on Christmas, 3 months before my dunk tank test:
(Photo no longer available)
That is me at 183 lbs. and I lost 3 lbs. of bodyfat before my dunk tank test. Now, at 31 years of age, I have 6 lbs. more muscle than in the above picture. Rather than lose muscle and succomb to the aging process, I have done the opposite! Now I just need to get rid of my excess bodyfat (without losing the new muscle) and the world will once again be right.