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Discussion in 'Hobby Electronics' started by Trevor Wilson, Oct 29, 2003.

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  1. Body fat analysis scales

    Jaycar P# QM7249 On special for $110.00.

    Mine arrived yesterday. Bloody rip-snorter. Nicely made and finished and the
    thing works well.

    I thought I could fool it, by standing on it with wet feet. Nope. It seems
    to have several sensors which compensate for skin resistance. Kinda like
    4-wire resistance analysis. Very impressive stuff. The last time I tried
    some of these scales out, they cost 500 Bucks.
  2. Ken Taylor

    Ken Taylor Guest

    You're kidding! I saw these advertised and assumed they were junk....must
    waddle out and get one!

    (the fat bastard)
  3. **I don't think they're junk. The weighing part is toughened glass, which
    adds nice 'heft' to the thing. The display is big and it's so easy to use,
    you can chuck the instruction book. The mass measurement part seems to be
    adequately accurate. I have no idea how accurate the fat measuring part is.
    They claim 05%. Seems a bit optimistic to me, given the method of
    measurement. As long as it provides a repeatable figure, I'm happy.
  4. David Segall

    David Segall Guest

    I think you will find that it is a fairly simple calculator. It uses
    your weight and the height and sex that you stored in it to compute
    body fat based on a table of ideal weights . Here's the general idea
  5. They will measure ok till you have used them a dozen times. Then the
    capacitive plates start bending and going out of cal. PS, I bet if you
    placed a calibrated mass on them they would not be all that accurate.
  6. **Nope. Wrong. This puppy is MUCH more sophisticated. It measures body
    resistivity. Lean muscle is less resistive than fat. I had already figured
    out that much. The trick is to calculate OUT the skin resistance. This set
    of scales does so, by measuring the skin resistance, then measuring the body
    resistivity. Nifty stuff.
  7. There are plenty of papers and reseach out there on these sorts of
    "bioimpedance" techniques. An AC signal is used, possibly at different
    frequencies. The calculations and models can get pretty complicated
    Jaycar also have a small hand held body fat analyser for about 25
    bucks, also available in many other shops too. I have tried one out,
    and while the readings are quite repeatable, the actual percentage
    figure was at least 15% (body fat % points) higher than it should have
    been in my case. So it seems that this one is a heap of junk, but
    might be ok for relative measuremets over time. I have read that the
    legs are the best place to perform the measurement, as they contain
    much greater muscle bulk, and the leg muscles somehow conduct more
    repeatably. I have found the feet based units to be quite repeatable
    between different brands, and they give sensible figures compared with
    traditional tests.

    Dave :)
  8. David Segall

    David Segall Guest

    Try this Trevor. Stand on a piece of glad wrap or a piece of aluminum
    foil. I bet your scales will even give you the same answer then.

  9. **You'd lose that bet. I tried an insulator (a newspaper) and the scales
    reported an "Error" message. Think about the alfoil thing.

    BTW: Alfoil does affect the figures slightly, but not as much as a cursory
    thought would provide.
  10. **I don't know if you took notice of my original description of the scales.
    Anyway, I'll elaborate:

    * The instructions are very specific that bare feet must be used.
    * Under each foot, are three conductors, which contact the feet, when in
    * The scales take a little time for measuring weight (about 3 seconds), but
    around 10 seconds to calculate body fat.

    I'll put the 'scope on the scales over weekend and look at the potential
    difference (if it exists) of the conductors, when measuring.
  11. David Segall

    David Segall Guest

    OK Trevor, I resile. I'll go out and buy one.
  12. eug k

    eug k Guest

    Whatever anyone does, don't get the small handheld one. I bought two, one
    for a friend, and both were absolutely crap. They gave about the same
    reading no matter who used them - even when I shorted the two plates together
    with some wire. It said my very skinny friend was overweight. In fact, it
    said everybody was overweight. Both units did that. Needless to say, I
    returned them.

    Tanita body fat scales, which seem to be the most well known around, have
    been at the $2xx mark for quite a while now. am quite sure Rebel Sport have
    a $160'ish model.

    Would it be possible for you to test out the accuracy of the scale?
    Any idea if the body fat measurement is accurate?

  13. mikegw

    mikegw Guest

    As a total guess I would think they would be alright for measuring one's
    relative change in body fat. As it measures from one leg to another it
    must( Guessing here) only measure body fat stored in the legs. I would
    think that x% body fat on some one who is "top heavy" would read lower than
    someone who is "bottom heavy".

  14. Ken Taylor

    Ken Taylor Guest

    Well, I'm bottom heavy, so I'm told. :) I have a friend who's a dietician
    and she uses an electronic scales type of body-fat analyser, says they're
    accurate, but obviously that'll depend on brand, etc. Not sure about the
    Jaycar one obviously, but I may give it a try and compare with the gym
    measurement using the (ouch!) calipers.

  15. There has been a lot of research into this, and some of the papers
    make fascinating reading. Apparently there is a fairly solid
    relationship between the leg bioimpedance measurements and overall
    body fat percentage; for given population averages, ages, sex, weight
    etc, which is why the units need to know this information.
    No body fat test is 100% accurate and comparative, let alone these
    bioimpedance units. But it looks as though the technology is fairly
    mature these days that the repeatability and correlation with other
    traditional tests is pretty good. Definitely better than the skin fold
    test anyway, which is pretty much what these units are designed to
    But as you mentioned, as a relative measure they are pretty good.
    You can pay $$$$ for professional units too, don't know if they are
    any better though.
    The reading will also change before and after excercise, meals,
    showers etc, so if you want the best reapeatability it's best to use
    it the same time and under the same conditions every day.

    Dave :)
  16. eug k

    eug k Guest

    OK I just picked one up today.

    Trevor, would your bodyfat reading happen to be in the 23-24% range?

    The scale is reminiscent of the handheld fat monitor that I tried a few
    months back. No matter who uses it, it'll return a figure around 23-24% -
    even if I shorted the two probes! It said my obviously skinny friends
    were overweight, haha..

    I did the same with this scale - I placed an aluminium flat across it and
    measured the resistance between the left and right "sensors" (the three
    tracks are connected to each other) to confirm that the sensors were being
    shorted. Did the fat test, and surprise, 23.1%.

    I squatted on the scale in such a way that my feet didn't touch the sensors,
    and lightly placed my fingers on the sensors hoping to stuff up the
    reading. I got 22.8%.

    What sort of figures am I meant to get if I short the sensors? I assumed it
    should cause an error.

    I'm gonna try it with my skinny friend today. I have a feeling I'll get the
    same problem as the handheld one... probably gonna return it tomorrow!

    Weight-wise, it does seem to fluctuate a bit. A Tanita (they seem to be the
    standard in bodyfat scales, and they're also known for accurate weight
    readings) says I'm 67.2kg. The Jaycar one I tried at the store also said
    67.2kg, but the one I brought back says 66.1 to 66.5kg. The tanita says 8%
    body fat, the jaycar one says 23%. Both scales were used within two hours
    of each other, on flat ground.
  17. Ken Taylor

    Ken Taylor Guest

    While I find the 8% body-fat figure hard to believe, unless you're a *real*
    keen marathon man, the 23% figure shows admirable consistency. :)

  18. budgie

    budgie Guest

    Shite!! You been eating Big Macs solid for two hours? Wotta hero!
  19. Exactly the same here.
    I'm 7% - 8% with various foot based models, which is pretty much right
    for me based on other methods too.
    The crappy Jaycar handheld one shows around the 25% figure
    consistantly. The same with other people I have tried it with too.
    Body fat measurement is far from an exact science, and various greatly
    with individual circumstances, but the Jaycar hand held unit isn't
    even in the ball park.

    Dave :)
  20. A body fat figure of under 10% can be quite common with males,
    especially those of lean build and/or with considerable muscle bulk

    Dave :)
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