# Hydrostatic Weighing (Formula help)

Hydrostatic Weighing (formula help)

Today i got my % body fat done first with skinfolds (calipers) and i came out to 3.9% when one person did it and around 4.5% when someone esle did it.
Thats right arond where i wanted and expected to be.

I then did underwater weighing and i weighed 3.6 kg underwater. This is where i need your guys help.
There is a long formula that i do not have the knowledge and math skills to do so if anyone has a texbook or knows this formula and can figure out my percent here is the data.

Weight:153 pounds 69.5 kg.
Height:67 inches
Age-21

Water temp in celcius-13 degrees

Weight underwater with out the equiptment- 3.6 kg

Bodyfat testing is error prone to the point that the true formula is BF= BS
Hydrostatic testing assumes ther is a common density for muscle (there isn’t)
Skinfold tests vary according to the skill of the tester and the time he/she leaves the calipers on.
If you’re lean, you’ll know it!

I agree body fat measures are very inaccurate, but if you really want I can calculate it out for you. But I need one more piece of information, your vital capacity; this is used to estimate the amount of left in your lungs.

thanx paul, if you can do it for me thatd be great. id appreciate it.

how do i know my vital capacity? isnt there a formula to find out that too?

You will need to measure it, at my school we use a Collin’s Vitalometer to measure them. You would need a similar device, basically it’s a machine that you blow as much air into and it measures that amount.

hmmmm,
i dont think we have that. is there a way to estimate based on height and weight. And how much does that vary?

Ok, I calculated it out for you, but keep in mind the testing to begin with is really inaccurate, coupled with that fact that I’m estimating a piece of the data it increases the inaccuracy. Anyways, you’ve got a 13.78% body fat according to the calculations.

hahaha. cool.
paul you must be a math genius. that forumla was way to long and complex for my math skills. Thanx for taking the time anyway though.

How innacurate is underwater weighing? Cause isnt it weird that with skinfolds i was 4%. And if you seen me. You see im def under 7%.

I’m a human kinetic student, I’ve had to do body fat percentage calculations a few times before, and I’ve had to take a few math classes, people get intimidated by formulas often times they are simpler then they look. As for the reasons for the inaccuracy of the test, there are a number of factors, one if how comfortable the person feels underwater. If there not that comfortable they could be swaying in the water causing inaccurate readings, also if the person does not blow out all of the oxygen in their lungs, which is difficult to do while underwater for many people. If I were you I would concentrate on having the proper somatotype for a sprinter, not what percentage body fat you are.

Thanx for the info. I didnt really do this just for my own info. I am an exersise science major and this is one of the tihngs we were doing in exersise physiology. So i volunteered to be a subject.

Ahhh exercise Phys, one of my fav courses in school. Its been about 3 years since I took it. I had the God of Physiology teach me, Dr. David Hood (this is his website http://www.yorku.ca/dhood/). Have you guys covered sub-max VO2 test on the bike?? Pretty fun stuff and then evetually you should cover ECG charts and a bunch of other stuff too.

About hydrostatic weighing CF and Paul are both very correct, its a procedure that can be very innacurate and not suprisingly can potentially have a big margin or error ranging over a variety of factors. Yet, should not be a procedure to overlook since you can extrapolate any number of useful information necessary for an assessment of the sedentary person or elite athlete.