First placed on the Internet in March 2005.|
This method of determining bodyfat percentage is so much fun that kids will generally be reminding their parents when they get to do it again! And it is so accurate that a weekly or monthly Progress Chart can show real-time improvements or back-sliding! In 5 minutes of fun, our young ladies determine their average body density to an accuracy of one part in a thousand! (The older girl in the PSA determined that her average body density was between 1.0056 and 1.0067 gm/cc in this fun activity! She was pretty athletic and then weighed about 90 pounds, where here Bodyfat was then 21.9%, all in just five minutes of fun!) There are few research labs that can match that precision!
A set of Public Service Announcements (PSAs) are available to air on many television stations, which show how this method works. The following discussion follows the storyline of those PSAs.
Here are also some streaming video files of the PSAs:
If they or some neighbor has a swimming pool, we have designed a set of Batons which are actually discarded Pepsi bottles with some pennies in them, where in an hour, the whole set of needed Batons can be assembled! (Instructions are linked below.)
As is convenient to the parents, they could also go to a nearby YMCA, or a local Health Club or a local Public High School or Park Department swimming pool. No knowledge of swimming is necessary!
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For any of these facilities, there is not even any significant cost involved! For a High School, less than $50 of materials (from a local home supply store) would provide a Shop Class a very interesting project, since this web-site provides for free all the directions needed to assemble the needed Batons. Health Clubs could have their Maintenance Personnel make them. The point is that for as little as $50 total expense, any of these 74,000 facilities could offer this wonderful service to their local community.
The Lifeguard will not have any special responsibilities for this family's activities. He/she will be able to watch the entire pool, as normal. As far as the Lifeguard is concerned, these kids are no different than anyone else in the pool.
The Batons A through X are in order as to their weight. Behind them, you can see the two much larger (and heavier) Y and Z Batons which are only needed for people who either have an extremely high bodyfat percentage or they weigh far more than any kid probably should! (They are primarily intended for some adults.)
Near the back of the rack, you can also see the float and FLOAT Batons, which only need to be used for kids or adults who naturally sink in a pool.
The storage rack we have used has a specific place for each of the Batons, with matching letters that show where they each belong. However, a different sort of storage rack could be used, even just lining them up on a shelf or the pool deck. The rack shown has the advantage of having a letter on the rack right under each Baton, so it is obvious to where it is to be returned.
The storage rack is not right at the pool, but in a location where people would not stumble over it.
When the child in the pool does this, he/she starts out simply standing. Once the feet are lifted up off the bottom of the pool (to curl up into that ball), the child either floats or sinks, and part of the back is either visible or not visible above the water. Simple! The idea of this "game" is to find the LOWEST LETTER BATON (or largest Float) that will stop you from floating with your back above the water. So the person in the pool can try holding ANY of the lettered Batons to see if you float or sink, or no Baton at all, or even one of the Float Batons, usually with one of the lettered Batons, too.
Once the feet are lifted up off the bottom, only three things are possible!
(1) The child could float. In this case, she is holding the (now obsolete and no longer used) '&' Float and the 'E' lettered Baton, and a portion of her back is visible above the water (this indicates that the average density of the child plus Baton(s) is slightly less than that of the water of the pool). She would either need to try to blow out (exhale) more air from her lungs or use a heavier (higher letter) Baton and try it again. Since each try only takes a few seconds, it's "no big thing!" Since this is a "competitive game" to kids, they may want to try several times to blow more and more air out of their lungs, to be able to use the lowest letter Baton!
(2) The child could sink, clearly going down toward the bottom. This indicates that a lower letter Baton could be tried, in other words "winning"!
At any time the child could simply let go of the Baton if there was any fear, to immediately bob up to the surface. And just putting the feet down and standing up works too, to get the head above the water!
(3) Or the child could sort of "hover", in this case while holding the (now obsolete) '&' Float and the 'F' lettered Baton, without really floating or sinking very fast. This last situation is the goal. With this situation, the combination of the child and the Baton(s) have EXACTLY the same "average density" as the water in the pool. That water's density is precisely known to be 0.9978 gm/cc (not actually 1.0000 gm/cc because the water is warmer than 39°F). The Batons are all precisely designed, so there is certainly ONE of the Batons that will permit this hovering (or very slow sinking)!
From the kid's point of view, it represents the SMALLEST LETTER Baton (or largest float) where she is not clearly floating.
It is NECESSARY to exhale all the air possible from the lungs in order to get really accurate results. If a child does not exhale much air, that air in the lungs acts as an extra "float" and then ALWAYS makes it necessary to use a higher letter Baton to stop floating! Exhaling more means a BETTER SCORE! In the first several weeks of doing this, nearly all children's Progress Charts will seem to show impressive improvements in Bodyfat Percentage, but it is probably misleading! As a (competitive) child wants to "get a better score" than last week, she tends to LEARN to force more air out of her lungs. That way she gets a "better score"! So it is commonly several weeks (of competitive practice!) before a child is exhaling ALL the air they can, and in the meantime, their Progress looks very impressive! Once they are exhaling all that air (there is ALWAYS some air that remains in the lungs, but it is a pretty constant amount and does not affect this process), the precision of this system starts to really show. Since each week's results is generally accurate to better than ±1%, the Progress Chart shows any "trends" toward better or worse bodyfat percentage. This does NOT mean that any specific week might be off that line (usually higher) because the child might not exhale as much air that week, or he/she might have just drunk a carbonated soda or recently eaten something that makes intestinal gas. The point is, the TREND of the line on the Progress Chart is extremely reliable.
The child's dry body weight (on a standard scale) (in this case around 80 pounds) and the letter of the Float and Baton (in this case the [now obsolete] float '& + F') are then looked up on an Analysis Chart. No complicated calculating ever needs to be done (because it was already done earlier for you!) The Analysis Chart is set up like a simple multiplication table, and the Bodyfat Percentage is simply the number in the box where the Weight (80) and Baton Letter (F) cross. There are a whole series of Analysis Charts, which have pre-calculated figures for every possible person between 30 lbs and 400 lbs, and they are provided (as DOC files) in this web-site (from the main Bodyfat web-page linked below here). Any computer can simply print out a copy. We recommend that it then be laminated to keep it from getting wet!
Actually, for home use, we now provide an automatic Bodyfat Calculator, where you just type in the body weight and pick out the Baton(s) used, and it does all the needed calculations for you.
If they or some neighbor has a swimming pool, we have designed a set of Batons which are actually discarded Pepsi bottles with some pennies in them, where in an hour, the whole set of needed Batons can be assembled!
Concept developed, and script written by: Carl Johnson
Public Service Announcement (PSA) created by:
Governors State University Media Department, headed by Prof. Dan Nearing
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 ±10% being expected. It only provides a ball-park 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 ±10%, and the Batons-Floats can get you within about ±1%.
Bodyfat - Combating Childhood Obesity Through Motivation (specifically directed at Childhood Obesity)
The Bodyfat - Simple and Accurate Measurement - PSA Storyline of the 30-second and one-minute PSA (Public Service Announcement) TV presentations.
The page that provides the PVC construction details for the Batons
and Floats and all the printable Analysis Charts is at:
Bodyfat Analysis Weights - Filled PVC Plastic Batons http://mb-soft.com/public2/bodyfwp2.html
The page that provides the construction details for the Pepsi bottle-based
Batons and Floats and all the printable Analysis Charts is at:
Bodyfat Analysis Weights - Pepsi Bottles and Pennies http://mb-soft.com/public2/bodyfwp3.html
The page that has the Bodyfat Percentage - Determining Accurate Bodyfat Easily Automatic Calculator which uses the Baton/Float letters and the dry body weight
This presentation was first placed on the Internet in March 2005. The main presentations of the concept were already on the Internet in the indicated pages from Febraury 2003.
C Johnson, Theoretical Physicist, Physics Degree from Univ of Chicago