Anyone done a hydrostatic (underwater) bodyfat test? Can you make a rig at home?

[carpenterman]

My question, what all steps were involved? Was it just weighing above and also underwater, and then doing a calculation, or was there more to it than that? And do you think it could be done at home?

I've been hearing that this is the gold standard, yet it is expensive and hard to find. However what stops someone from simply getting one of those hanging scales, and suspending it above a source of water. Either a hot tub, off the side of a dock on a lake, or if your ghetto just fill your yard waste bin with water.

Simply getting a dry weight and underwater weight, and then doing a mathematical calculation just doesn't seem that hard to me. I thought lots of people would do it, but I can't find any DIY hyrdostatic test setups on the web. Is it more complex than I'm thinking?

[SkydogGinsberg]

That's an awful lot of hassle for a constantly changing variable that doesn't require a lot of precision (and only requires "ballpark" accuracy) to adequately manage. As "home construction" projects go, an actual home gym is far more worth the effort. For what are you needing "ultimate" accuracy?

[phrali]

if i had the money to build something like that, i wouldnt build it. i would buy one of those eleiko competition sets i want one soooooo bad

[DeltaCharlie75]

Why the feck would you bother?

[Mdenatale]

Weigh yourself normally

Then use a spring scale in your swimming pool

Then use this:
Body Density = dry weight / [((dry weight - wet weight) / water density)- RV - 0.1]
(RV is the volume of air in your lungs)


Then choose the formula you prefer:

Siri Percent Fat = [(495 / Body Density) -450] * 100

Brozek Percent Fat = [(4.570 / Body Density) - 4.142] * 100


Then come to the conclusion this was way more work than it was worth just to get a marginally accurate result even if you did everything perfect.

[carpenterman]

Weigh yourself normally

Then use a spring scale in your swimming pool

Then use this:
Body Density = dry weight / [((dry weight - wet weight) / water density)- RV - 0.1]
(RV is the volume of air in your lungs)


Then choose the formula you prefer:

Siri Percent Fat = [(495 / Body Density) -450] * 100

Brozek Percent Fat = [(4.570 / Body Density) - 4.142] * 100


Then come to the conclusion this was way more work than it was worth just to get a marginally accurate result even if you did everything perfect.

Thats exactly what I was looking for. But I have a couple questions.
1. Why would it be only marginally accurate? Hydrostatic testing is supposed to be one of the most accurate methods.
2. Your formula mentions RV, volume of air in lungs. But how do you figure that out? Shouldn't it be pretty low since your supposed to exhale as much as possible?

As far as people saying why do it, or its too expensive. It seems to me like it only costs the amount of a spring scale. I'm sure you can find a spring scale for much cheaper than it would cost to have it done even one time professionally, and then you could do all your friends, and measure yourself each month for free, etc.

[Mdenatale]

Thats exactly what I was looking for. But I have a couple questions.
1. Why would it be only marginally accurate? Hydrostatic testing is supposed to be one of the most accurate methods.
2. Your formula mentions RV, volume of air in lungs. But how do you figure that out? Shouldn't it be pretty low since your supposed to exhale as much as possible?

As far as people saying why do it, or its too expensive. It seems to me like it only costs the amount of a spring scale. I'm sure you can find a spring scale for much cheaper than it would cost to have it done even one time professionally, and then you could do all your friends, and measure yourself each month for free, etc.

Problem is that even when done correctly this method is only slightly more accurate than the skin fold method. And the residual volume of air in the lungs is a major source of inaccuracy. You need special equipment to measure that too, a spirometer and helium analyzer. If you make any assumptions about this value you will have poor accuracy. In reality getting the dry and wet weights is the easy part.

UVM describes goes through the whole process here: http://nutrition.uvm.edu/bodycomp/uww/uww-toc.html

[SkydogGinsberg]

As far as people saying why do it, or its too expensive. It seems to me like it only costs the amount of a spring scale. I'm sure you can find a spring scale for much cheaper than it would cost to have it done even one time professionally, and then you could do all your friends, and measure yourself each month for free, etc.

Why is it worth the extra effort, regardless of monetary cost? Trying to assess, for example, initial TDEE based on BF, "ballpark" is good enough. For a 200lb lifter who's between 20-25%, that 5% differential amounts to ... 150 calories.

- or -

'Bout a single slice of sourdough bread.

[magician27]

My question, what all steps were involved? Was it just weighing above and also underwater, and then doing a calculation, or was there more to it than that? And do you think it could be done at home?

I've been hearing that this is the gold standard, yet it is expensive and hard to find. However what stops someone from simply getting one of those hanging scales, and suspending it above a source of water. Either a hot tub, off the side of a dock on a lake, or if your ghetto just fill your yard waste bin with water.

Simply getting a dry weight and underwater weight, and then doing a mathematical calculation just doesn't seem that hard to me. I thought lots of people would do it, but I can't find any DIY hyrdostatic test setups on the web. Is it more complex than I'm thinking?

i would just look at mirror, bodyfat % is just a number. who cares..