13 Weeks: Tool Time

Week 9 of my second 13 week season: low carb diet and more exercise, tracking my weight, blood glucose, and body fat. You can follow me at my 13 Weeks Facebook page for daily updates, and you can join Fitocracy (free!) and follow my daily exercise, and maybe even start tracking your own.

When I started off on this second 13 week experiment, I decided I was going to emphasize losing body fat as well as glucose — and yes, my weight, I just can’t resist. There are a lot of ways in which we can measure body fat.

You can measure your waist and neck size and apply an empirical formula. This is the method the Army uses, and studies have shown it’s reasonably accurate.

You can take skinfold measurements with a calipers, and compute the result with a different empirical formula. This is a bit more accurate than the Army method (although not much).

You can have your body density measured by weighing yourself, and weighing yourself totally immersed under water. This is the “gold standard” method medically, but it’s not very practical at home.

You can go to a radiologist and have body composition measured by taking a full-body X-ray. This is called DXA body composition. (The link is to the radiology practice of which PJM contributor Paul Hsieh is a member. Just a random plug.) This method is very good but has several disadvantages: you certainly can’t do it at home, it means making an appointment and getting the full-body X-ray done, and it costs half a grand.  Or, 

You can use an impedance method device. This works by sending an alternating current through your body and measuring how the current flows. (I was going to write a description of what impedance is and how this works, but I kept falling asleep.) Never mind how it works, basically current flows more easily through muscle and bone than through fat, so the more fat you have the more you resist.

Here are the tools I’ve been using.

MyoTape Measuring Tape

Measurements are fairly straightforward. I bought a MyoTape measuring tape, which is supposed to make it easier to take the measurements for yourself. It’s a white plastic object with a spring-loaded measuring tape. You wrap the tape around yourself, hook the end of the tape back into the plastic body, and then pull it tight. In theory, then you unhook the tape and read it.

In my arrogant opinion, this device basically sucks. The problem is that when you release the tape, the spring loading pulls in the tape until it catches a ratchet of some sort. This can be anything from a half inch to an inch. You’re better off with an old-fashioned sewing tape. Amazon has a bunch of them — in fact if you have eleven friends, you can buy twelve of them for about 50 cents each.

Skinfold Calipers

Skinfold calipers are supposed to be a good method. You pinch up a fold of skin and measure its thickness, then use a chart (or compute a somewhat complicated formula) to get your percent body fat.  I got one from Amazon for about $15.

But here’s the problem: it’s almost impossible to do yourself. One of the measurements you should take is on your back around your shoulder blade, and I defy anyone but a stage magician or a contortionist from a Chinese circus to do that for themselves, and I have completely failed to teach my cats to do it for me.


So that leaves the bio-impedance method. There are lots of devices for this; I bought a Withings scale. It basically runs the current from one foot to the other while weighing you, then connects to your wireless network and sends the data home, where you can look at it on the web.

This seemed to work well — for a while. Now, even when it’s working well it has its problems. It’s very sensitive to how well hydrated you are, and it’s also sensitive to how long you’ve been upright — the distribution of fluids in the body changes. So I got fairly rigorous about weighing and taking body fat a half-hour after getting up, but that was a little annoying because it meant a half hour in the morning waiting for my first cup of coffee, drink of the gods. Oh, well, anything for science.

Then I noticed my bodyfat was starting to vary wildly, after having settled down to a reasonable measurement. So I tried an experiment: I measured 5 times at one minute intervals. Over the span of 4 minutes, I got the following:


There are a lot of variables that can affect body impedance, but none of them change that much over four minutes.

I contacted Withings, and after a couple of tries at resetting the scale, they’ve agreed to send me a new one. It turns out this scale has been discontinued (I wonder why?) so I’m getting a new one, called a Withings Smart Body Analyzer. It not only gives weight and body fat, it measures your heart rate and indoor air quality. Whoo-hoo.

As we used to say in grant applications, more research is needed.

So here’s the table this week. You’ll notice that unlike last weeks table, March 14th doesn’t repeat three times.

Date 7 day Weight 7 day Glucose 7 day Bodyfat Sum Fitocracy Points Weekly Fitocracy Points
2013-02-01 272.50 116.43 33.1 447 447
2013-02-07 272.63 114.57 30.79% 1881 1881
2013-02-14 271.91 110.43 30.36% 2606 725
2013-02-21 273.79 115.29 29.16% 3775 1169
2013-02-28 274.44 104.00 30.00% 4929 1154
2013-03-07 273.11 115.86 30.24% 6022 1093
2013-03-14 269.86 101.86 30.10% 7233 1211
2013-03-21 272.08 112.25 30.64% 7681 448
2013-03-28 270.57 113.86 30.26% (??) 8180 499
2013-04-04 271.31 103.86 29.95% (??) 8404 224
Δ since 2-1 -1.19 -13.00 -3.15% N/A N/A