Bodyfat Analysis Weights  Filled PVC Plastic BatonsThere are three possibilities! The first involves YOU cutting off many pieces of PVC water pipes of various sizes to the lengths as indicated below. You would need the standard PVC cement ($3) and a lot of PVC pipe end caps, and sandpaper and some experience in assembling PVC pipe. You would also need one bag of SANDMIX concrete mix (usually comes in a 60pound sack for $3) (and some experience in mixing concrete!) Altogether, the materials would cost you around $50 for a whole set of the batons. It can be an interesting and fun project, but a good deal of time and effort is involved. The second and third of these possibilities are where a small company would assemble those batons for you, the last of which would also include a precision calibration of that specific weight set, creating a set of batons that are especially accurate (usually better than 0.1% regarding accuracy of bodyfat analysis), and even a unique set of Analysis Charts created just for those specific batons. As with the steel rod weight sets, you would only need to hold a maximum of two of these plastic batons. This method has the advantage that if a baton is dropped (or thrown) it is cushioned by the plastic and shouldn't chip a pool deck tile or seriously hurt anyone. They are also pretty much indestructible. This approach is the most work and would cost you a little more but it should provide an accuracy of around 1% (and even better for the calibrated set) regarding the bodyfat percentages. If you intend to regularly measure your bodyfat percentage (every week or every month), and you do not want to go to a YMCA or Health Club and have a swimming pool or (freshwater) lake, this might be a logical choice, although it is a lot of work. The excellent accuracy (and repeatability) can give better feedback about your success in your Progress Chart! In principle, you could preestimate which batons YOU might need and only make a few of them, saving yourself time and effort! However, the amazing precision of this system is so great that you could realistically go through the entire alphabet as you learn to expel more air, so you may still eventually need the whole set. And, if you have your own swimming pool, your friends, relatives and neighbors will certainly want to learn their bodyfat, so you might as well make them all! It is our hope that enough YMCAs and Health Clubs near you will have the precision (calibrated) set of bodyfat batons and that they will offer either a free service or a nominal ($1) charge to test bodyfat analysis, such that few people would see reason to need to make their own!


ConcreteFilled PVC Plastic Baton Weights  Letter  

1/2" standard PVC pipe 4.875" long  A  
1/2" standard PVC pipe 9.75" long  B  
3/4" standard PVC pipe 8.75" long  C  
3/4" standard PVC pipe 11.875" long  D  
3/4" standard PVC pipe 15.0" long  E  
1 1/2" standard PVC pipe 5.75" long  F  
1 1/2" standard PVC pipe 6.75" long  G  
1 1/2" standard PVC pipe 7.75" long  H  
1 1/2" standard PVC pipe 8.75" long  I  
1 1/2" standard PVC pipe 9.75" long  J  
1 1/2" standard PVC pipe 10.75" long  K  
1 1/2" standard PVC pipe 11.875" long  L  
1 1/2" standard PVC pipe 12.875" long  M  
1 1/2" standard PVC pipe 13.875" long  N  
1 1/2" standard PVC pipe 14.875" long  O  
2" standard PVC pipe 9.25" long  P  
2" standard PVC pipe 9.875" long  Q  
2" standard PVC pipe 10.50" long  R  
2" standard PVC pipe 11.125" long  S  
2" standard PVC pipe 11.75" long  T  
2" standard PVC pipe 12.375" long  U  
2" standard PVC pipe 13.0" long  V  
2" standard PVC pipe 13.75" long  W  
2" standard PVC pipe 14.25" long  X  
two standard PVC pipes above  X+A  
two standard PVC pipes above  X+B  
two standard PVC pipes above  X+C  
two standard PVC pipes above  X+D  
two standard PVC pipes above  X+E  
two standard PVC pipes above  X+F  
two standard PVC pipes above  X+G  
two standard PVC pipes above  X+H  
two standard PVC pipes above  X+I  
two standard PVC pipes above  X+J  
two standard PVC pipes above  X+K  
two standard PVC pipes above  X+L  
two standard PVC pipes above  X+M  
two standard PVC pipes above  X+N  
two standard PVC pipes above  X+O  
two standard PVC pipes above  X+P  
two standard PVC pipes above  X+Q  
two standard PVC pipes above  X+R  
two standard PVC pipes above  X+S  
two standard PVC pipes above  X+T  
two standard PVC pipes above  X+U  
two standard PVC pipes above  X+V  
two standard PVC pipes above  X+W  
Precision floats, for people who naturally sink  
9.75" long 3" diameter empty PVC pipe with caps  float  
11.25" long 4" diameter empty PVC pipe with caps  FLOAT  
These floats can also be made out of 1" thick blue foam building
insulation. The 'float' would be cut as a rectangle of 6" by
12.5". The 'FLOAT' would be cut as a rectangle of 10" by
15". Such floats are not very durable and are fairly easily
damaged, where chunks can get lost and their accuracy then degrades.
 
An Optional 'Y' baton for larger people  
3" standard PVC pipe 16.375" long  Y  
An Optional 'Z' baton for larger people  
4" standard PVC pipe 13.125" long  Z 
NOTES:
This entire set provides 264 different values that can be used
for determining the Average Body Density and then the Bodyfat Percentage,
72 involving net flotation and 192 that involve net weight. This range
should be sufficient for virtually any person.
These all use PVC pipe and NOT CPVC pipe, which is a different diameter and would make incorrect weights. These dimensions are also based on COMMONLY AVAILABLE PVC pipes, which means 'Schedule 40' for the larger diameters but the thinner walled PVC pipe that is generally available today (which is NOT Sch 40). We recommend using PVC end caps that are flatended and not rounded (like NIBCO D2466, which is very commonly available). The pipe lengths are first cut to length (shown above), and the edges sanded to remove burrs. When the solvent cement is applied, it is important to push the cap on COMPLETELY. You only have a couple seconds and if it gets crooked, it might only go on part way. That would make the space for the concrete larger and make the weight incorrect. When this happens as the second cap is added, an air bubble would be left inside which also would make the weight incorrect. This is especially a problem for the larger diameter pipes, as more force is needed to force the cap to bottom out.
Next, the premixed sandmix concrete must be properly mixed and poured or pushed into the open end of the pipe. Following standard concrete mixing guidelines, the mixture should not be 'soupy' and not too dry. Variations in this can affect the accuracy of the Analysis Charts. The pipe should be regularly shaken to eliminate any air spaces down inside the pipe or a straight piece of a coat hanger could be used to eliminate any air spaces by stirring. The concrete is filled to the top, and the pipes stood up until the next day when the concrete has cured.
At this point, everything is cleaned really well, and the other end cap is to be installed. But first, a VERY small hole (1/16" is fine) MUST be drilled through the center of that cap. Otherwise, the air trapped inside the cap would not allow the cap to be pushed all the way down, and a large air bubble would remain inside, which would seriously affect the accuracy of the Analysis Charts.
These various issues, along with the possibility of slight variations in the density of concrete due to variations in mixture of the sand and cement and water, are the reasons why a full calibration is probably appropriate for Health Clubs or YMCAs where many people would use them. It also turns out that there are normal variations in the exact inside dimensions and wall thickness of the PVC pipe which also can affect the precision.
In general, the Optional Y and Z batons may not be needed, as they are necessary only for larger people. You might look at the Analysis Charts (linked below) to see if you might need to use a Y or a Z baton. Not counting the Y or Z baton, the majority of the 60 pound bag of concrete mix is used! The entire set weighs more than that!
You may have noticed that there are consistent patterns in the lengths of consecutive tubes of the same diameter. You can use this fact to check the Batons you make. The end caps generally have a line around them. If you measure the distance between the two end lines, for each of the finished Batons, you should see the same consistent pattern. If one happens to be 1/4" or 1/2" longer than it seems like it should be, it probably has a big air bubble inside and it would give wrong values! Even lining them all up, you should be able to see if one appears to be a little too long!
The foam floats would be of no use at a Public Pool, as they are pretty easily broken or damaged, and probably would not last a day! But for a personal pool, they may last fairly well! But even if one gets damaged, making a replacement is pretty easy!
Brozek formula is: (4.57/(body density)  4.142) * 100
Siri (2compartment) formula is: (4.95/(body density)  4.50) *100
These formulas are a little misleading. First of all, they absolutely require expelling ALL the air possible from the lungs, something that takes some practice to do very well. But then they have to be adjusted for two different effects that they never mention! Even after you expel all the air you can from your lungs, there is still a Residual Volume of air remaining in the lungs. This amount varies from person to person but it is assumed to be 1.2 liters of volume. If a man displaced 91 liters of water, this would represent an adjustment of adding 1.319% (.01319) to the measured body density. It would seem that they could have just adjusted the Siri 2compartment formula to become (4.886/(measured body density)  4.50) * 100. If this man's body density happened to be the same as the water (0.9978 gm/cc), we would therefore have different calculated values of: (Brozek) 36.9% bodyfat or (Siri) 38.6% bodyfat. The adjusted readings are therefore around 6% lower than above, but still VERY high numbers!
I can use myself as an example. After exhaling NORMALLY, I still float. I weigh 202 pounds (and am 6'2") (my waist is around 32" to 33", relatively slim). With that NORMAL exhale, I can usually just sink using the X+D Batons but usually still float with the X+C Batons. You can see from the website calculator that my average MEASURED body density is therefore between 0.9891 and 0.9895 (gm/cc). (Note that this is a precision of one part in three thousand!) From our website calculator, that gives an estimate of between 26.2% and 26.5% bodyfat. From the American Council on Exercise guidelines, this is a little above the very top end of Acceptable. I had spent a career as a semipro volleyball player (when it was lower) and the result seems to me to be within a few percent of reality.
You can calculate that the above (unadjusted) Brozek formula as giving 49.1% and the Siri formula as giving 51.8% for me! Since "morbidly obese" is 35% or higher, those formulas might suggest that I probably don't fit through doorways! (Have you ever seen a winning beach volleyball player who was spectacularly obese?) It seemed obvious that those simple and crude formulas are sometimes very inaccurate! By the way, on the BMI Chart (height/weight) I am at 26, surprisingly close to what seems actually true! However, there is a reasonable explanation! When I really exhale all the air I can, I can avoid floating with the 'float' Float and 'N' Baton. This means a measured body density of 1.0009. Our website bodyfat calculator gives a value of 26.6%, again in rough agreement with BMI and the other figure. With the adjustment for the Residual Volume of air in the lungs, the adjusted body density is 1.0139. This would give a Siri 2compartment bodyfat value of 36.5%. This is closer but still apparently about 10% higher than we think it really is.
Careful scientific study has been done on such formulas, and it has been found that the Siri 2compartment formula gives results that have a 95% confidence interval ranged from ±8.1% to ±12.0% bodyfat percentage, for different ages and genders studied, as compared to methods that are considered to give reliable results. So even though the Hydrostatic Weighing procedure provides excellent accuracy regarding the Average Body Density, these formulas for converting that to bodyfat percentages can have huge errors! And if the 95% confidence is sometimes off by 12.0%, that means that there are times when it is even worse than that!
When we discovered the large probable errors of such formulas, we developed a complex equation that is based on considering and analyzing each of the many different types of things that are inside our bodies (bone, blood, muscle, fat, organs, brain, skin, etc) and the quantities of each inside us. We feel that our very complex equations (about twenty factors, each of which has a density value and a volume value, or 40 total variables) are far more scientifically based than the formulas presented above. However, our bodyfat numbers tend to be less than the Brozek or Siri numbers seem to imply. We are still investigating this matter. Our website bodyfat calculator (linked below) uses our complex formula.
The main concept of our system is to know INCREMENTAL changes in average body density, which our approach certainly does to better than one part in a thousand. We didn't necessarily intend to generate truly precise NUMBERS claiming a specific bodyfat percentage. Once an average body density is determined, the different formulas (and our equations) give different numbers for bodyfat percentage, true. But again, what WE see as important is whether that number goes up or down, and not necessarily the size of that number! See the point? So you really could use the Brozek or Siri formulas with our system, and still see changes, good or bad, just that the numbers will be a lot higher.
As to being able to brag about some specific number as being YOUR bodyfat percentage, our research suggests that nearly any number you might claim has a high likelihood of being substantially incorrect. But we suppose that if it is a number that you LIKE, you will probably want to tell people what it is!
We expect to some day modify our equations, as better figures for organ densities and bone densities, etc, become available. This might especially be true for kids, who tend to have a higher proportion of dense bones! Well, we concede that SOME people will insist on using one or the other of those two formulas above, so we are providing (below) analysis charts which use those formulas. You are free to use any of the three, as they will all show improvements or backsliding equally well! Just stay with whichever one you start with!
They are also available as Word (DOC) files which can be printed out
and laminated to be around a swimming pool!:
For body weights of up to 130 pounds
For body weights of between 130 and 230 pounds
For body weights of between 230 and 330 pounds
For body weights of between 330 and 430 pounds
The Analysis Charts based on the Siri formula are:
For body weights of up to 130 pounds
For body weights of between 130 and 230 pounds
For body weights of between 230 and 330 pounds
For body weights of between 330 and 430 pounds
The (blank) Progress Chart is at:
Weekly or Monthly Progress Chart
There is another issue to mention. The Analysis Charts were created using certain assumptions regarding the proportion of different kinds of component materials in the human body, and also assumptions regarding the densities of those component materials. It turns out that some people, such as AfricanAmericans, generally have bones that are of higher density than in others. There are also different proportions of body components in different people, such as bigboned or petite body types. These things can cause a shift in the numbers found in the Analysis Charts. For example, many AfricanAmerican males might normally sink in a pool, due to their highdensity bones. Some kids tend to naturally sink too! That does NOT necessarily mean that they are "professional athletes" as the very low Chart percentages might seem to suggest! They just have different internal body structures from most people. Therefore, the Analysis Charts could possibly provide numbers that are actually lower than their actual bodyfat percentage.
However, for the purposes of this testing, that effect is essentially unimportant! The person will always have the SAME highdensity bones! Therefore, if the following week, a slightly lighter baton is needed (with the float baton) progress is still shown in a Progress Chart. The actual numbers might be lower than what is real, but any improvements or other changes will still be clearly seen.
For body weights of up to 130 pounds
For body weights of between 130 and 230 pounds
For body weights of between 230 and 330 pounds
For body weights of between 330 and 430 pounds
These values are true and accurate, without any mathematical assumptions regarding proportions of fat, bone, blood, etc, and without any assumptions regarding the precise density of those components. Technically, these values are all that are really needed for this system! However, the general public is less interested in claiming an average body density of 1.0074 gm/cc than in simply claiming a bodyfat percentage! Technically, these charts show WHY this system works and why it is so precise, although we realize that most people will never want to use them!
These density charts, and the other Analysis Charts, were calculated assuming that the the pool water was at around 72°F and therefore had a density of 0.9978 gm/cc. If the pool water was cooled to 39°F, its density would be the 1.00000 gm/cc that books indicate. We note that public pools are nearly always within a few degrees of the same temperature, but even backyard pools rarely change by even 10°F. It turns out that when you DO do the calculations, the difference between doing this in a 70°F pool and an 80°F pool, is less than one part in a thousand. Yes, that might cause the "one part in a thousand density difference" that we described above, but that tiny amount is usually only equal to about one Baton letter difference. And that's for a very cool pool compared to a bathwater pool! NOT a factor!
Have a "normal" amount of air in your lungs, NOT having severely exhaled or inhaled. And then simply float stationary! Your friend sees (or maybe even measures) how much of your head sticks out of the water! If you do NOT float and sink toward the bottom, your bodyfat is likely to be around 13% or lower. If your friend sees TWO INCHES of the top of your head above the water, you are likely to be around 24%. If your friend sees about FOUR INCHES (essentially to the very top of the earlobes), you are likely to be around 40%. If around SIX INCHES (essentially to the earholes, and your eyes are above the water) then you are likely to be around 57%. You might see from the large changes in bodyfat numbers due to rather small differences in the amount of the head being visible, that this method is only very approximate, with plusminus 10% being expected. It only provides a ballpark number!
We mention this because there are a LOT of people who have been told that they have 8% or 4% or 11% bodyfat, due to using the extremely inaccurate bodyfat caliper method or electrical impedance (methods absolutely proven to regularly be 15% off either way, so in other words, meaningless except for bragging purposes.) A person could try to alter this method by intentionally normally exhaling first, which makes you float around one inch lower, which would appear to give an estimate of around 6% lower. By attempting to exhale all the air you can, you can lower your body by about 3 inches, which can give the appearance of around 16% lower estimate. The point is that by simply altering the amount of air in your lungs, you could change this reading by as much as 16%, another indication of why the far more accurate and repeatable Batons and Floats is desirable. If you really want to believe that you are at 8% or 11% so you can brag to your friends, there are many ways you can create such a number. However, if you actually want a REAL number for bodyfat, this very crude method can get you within about plusminus 10%, and the BatonsFloats can get you within about 1%.
Combating Childhood Obesity Through Motivation (specifically directed at Childhood Obesity)
The page that has the Determining Your Accurate Bodyfat Percentage Bodyfat Calculator which uses the Baton/Float letters and the dry body weight can calculate the correct density and bodyfat values for essentially anyone between 30 pounds and 800 pounds and with essentially any percentage of bodyfat.
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