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Body fat Percentage.

Discussion in 'Advanced Scuba' started by Teljkon, Jan 17, 2014.

  1. Seymour Fisch

    Seymour Fisch Contributor

    # of Dives: 25 - 49
    Location: Vancouver, BC
    71
    17
    So, I did wade through the formulas, and awap and jbark hit the nails on the head: you were using the wrong value for Ww and the wrong units.

    So, assuming the 230lbs in the air and 12lbs of weight to get neutral in the water, this gives you a Ww of -12lbs. Converting to kgs to make the units work out, we get 104.55kg for Wa and -5.45kg for Ww. Plugging these into the first part of the formula (Wa-Ww)/Dw, we get (104.55 - (-5.45))/1.025 = 107.3 liters. That's an estimate of the volume of water you are displacing.

    That volume includes the air in your lung and your intestines, so you subtract that off. Since the units are in liters, we subtract about (1.2+0.1) liters (your estimate of your Rv and 100cc correction). So that leaves 106.0 liters as the volume you (and your equipment) displace in the water.

    Now, going back to the whole formula, we compute Wa/106, and that gives you your density, or 104.54/106 = 0.9862.

    Plug that into the body fat formula (which is an empirically fitted approximation), we get 495/0.9862 - 450 = 52% body fat. :shocked2:

    But you can see that with the right units, at least you're getting into the ballpark of a correct answer.

    I'm guessing that BCD has some buoyancy (I don't know, but do typical BCDs float when completely empty?), you might have had some air in the BCD, and did you do the weight check with your tank empty? An Al tank will be positively buoyant when it's empty, and that will throw the figures off, too. The problem with trying to compute body fat % from your scuba weighting is that the scuba weight is based on the entire system of you, plus all your gear (and your exposure protection if you had been wearing any). I'm also guessing the 12lbs is actually quite a bit more than your true Ww, since the Ww would be what you need to be exactly neutral while maximally exhaling, whereas your scuba weight assumes a normal breath and errs on the heavy side (since you can compensate with the BCD when diving).
     
  2. scububa

    scububa Contributor

    # of Dives: 500 - 999
    Location: St. Louis
    305
    36
    If you are looking for a fitness BF% number, even though they contain inaccuracies, there are very inexpensive plastic calipers available ($6ish). If you use them with a similar protocol, they should give you a way to monitor 'relative' changes. So, when you lose weight on a program, did you improve your BF also - type of monitoring. You can use 3 site measurements yourself or with assistance you can use the 7 site tables. There are plenty of web calculators out there with tutorials.

    If you are looking for a more refined number, you might be able to get a personal trainer with higher quality calipers to give you an assessment. As others have said, there is no method that is going to be 100% as all methods are statistical based at some level. Other than being butchered and rendered, you'll never know for sure :)

    So, for seeing if your program is having a BF effect, get some plastic calipers (I think I have a pair that came complimentary with some protein powder order) and monitor yourself. Seeing a 5% change to the good is much more useful to me that knowing if I am 22% or 19%.

    Y%MV
     
  3. Teljkon

    Teljkon Contributor

    71
    5
    actually the cutting edge foxfish, at this time for body fat scans is a DXA scan. I may go for one. I plan on using multiple methods to track body fat and then recording them as an average. As all of you know the greater number of samples you have for an average the more accurate it is. So this would just be one of three other ways of tracking it. my goal is to get lean and not loose muscle. So calipers, electrical resistance, tapes with formula and dive weight once i tweak the formula will all go on an excel sheet. I am also going to freak out some other diver one day and start undressing under water see what floats what sinks LoL. My weight that I dove las dive was actually 9 lbs they were short on 5 lb weights on the boat so I took a 5 and a 4. So fairly awesome that I am down that much from where I was.

    AND A HUGE thank you Seymour fish for showing me the light on my mistakes I am good at math but it is not my strong suite.
     
  4. Seymour Fisch

    Seymour Fisch Contributor

    # of Dives: 25 - 49
    Location: Vancouver, BC
    71
    17
    Cool! By dropping from 12 to 9lbs, quickly eyeballing that formula looks like it'd drop the "estimate" from 52% to about 45%. :D

    If only it were that easy to lose body fat in real life!

    (The advice from others will get you much more accurate numbers, at least until you do your underwater stripper act...)
     
  5. Steve_C

    Steve_C Contributor Rest in Peace

    # of Dives: 500 - 999
    Location: Raleigh, NC USA
    4,270
    2,915
    Two people with the same amount of fat could have different densities. The fat density itself varies a bit as I recall. Also some folks have larger and denser bones.
     
  6. danvolker

    danvolker Dive Shop

    # of Dives: I'm a Fish!
    Location: Lake Worth, Florida, United States
    5,884
    3,009
    In all of the sports world, bodybuilders are the most compulsive about % bodyfat, and they primarily use calipers....but they have a person skilled in using the calipers properly ( part science, part almost art). This is the quickest method with useful accuracy.

    I am pretty sure the OP is not trying to use this fat measurement for figuring weighting for diving--that this is really about fitness monitoring, which he hopes will enhance his health and future diving.

    As others have said, there is wide variability in bone density and lung volume, so predictions as to buoyancy in water fail by errors in estimating fat %, bone density, and lung volume. There is no substitute in diving for actually adding and removing weights with dive gear to achieve ideal weighting.

    If my current Atkins style diet continues to work as it has the last month, I will be back to the body fat levels I enjoyed from my 20's to 40's, where I could get in a pool with a bathing suit on, take a full breath, and then sink so fast that if I sank head first, I could seriously hurt my head on the bottom. Associated with this....sugar is the enemy....as are all carbs other than vegetables....and if you eat many vegetables, it removes the need for your body to burn fat. Eat just protein and some fat, and your body is forced to burn fat......Surprisingly, this has not even damaged my cycling on A1A, or the recovery from 30 mile long high speed rides.....if anything, the complete ABSENCE of carbs, translates to almost no soreness after an intense workout---meaning that much of the post workout soreness many people get was inflammation caused from excess sugar sticking and attaching to muscle and tendons--this being A.G.E. ( Advanced Glycation End Products).
     
    AfterDark likes this.

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