Friday, January 14, 2011

Scale factors

I am pleased to announce that NPR reported last night that gun and ammunition sales are up this week in the wake of the Tucson shooting. Surely now that our fellow citizens are better armed we will avoid the kind of disaster that befell that Arizona city last weekend.

Meanwhile the world of cycling mourns Peter Post, a Dutch rider who won Paris-Roubaix in 1964,- the fastest edition ever- and 65 six day races on the track (zesdaagsen). Later he became a team manager at Raleigh and helped Zoetemelk, Raas, Kuiper and Kneteman and even later at Panasonic, Planckaert, Anderson and Vanderaerden. I do remember that Peter was not popular as a racer in Belgium even though he occasionally teamed with Belgian riders like Patrick Sercu and Rik Van Looy, on the track. Many people thought he had tricks up his sleeve. I never figured out what these tricks were.

This morning I received an email from the go1 bike shop that read, "Your mountain bike wants to go 10 speed." Now I have a good relationship with my mountain bike so I went up to the garage to see if this was true, but no answer was forthcoming. Surely this will soon change as I read that Samsung has introduced the RF4289 refrigerator that tweets when the milk runs out. How long until my mountain bike will tweet and let me know that it wants to go 10 speed? I just hope it won't throw a tantrum when I say no.

From: Go1 bike shop
Subject: Your mountain bike wants to go 10 speed
Date: January 14, 2011 7:19:00 AM PST

And to stick with the world of gadgetry, no gadget is more beloved by endurance athletes than the bathroom scale. Since weight is the key success parameter and scales keep track of weight, scales occupy a special place in our lives. So it is not surprising that scale manufacturers set out to improve the bathroom scale. And one of the latest fads is the addition of a body composition suite. Tanita is the premier brand here it has aligned itself with Ironman, the symbol of endurance and fitness.

A while ago I had several encounters with Tanita at Ironman Arizona. The story is instructive and characteristic of gadgetry so let me summarize it here. Tanita offered free evaluations for everyone willing to take off their shoes and socks to stand on the scale and fill out a questionnaire afterwards. The evaluations were done on their high end body composition monitor (model BC554) that sells for $129.99. The BC554 spits out a slew of numbers for you to worry about. It is easy to forget that weight is one of only two parameters it measures (the other is impedance).

My first evaluation came in at 177.6 lbs  body weight with 19% body fat. I was not happy and frankly a bit shocked that I harbored that much fat. The scale produced a slew of other values that struck me as wild guesses (how did it measure all that I wondered) but here they are: body water 53.7%, muscle mass 136.6 lbs, physique rating 9 (very muscular); metabolism at 1,879 cals per day and metabolic age 15. Bone mass 7.2 lbs and visceral fat rating at 4. All these were within normal ranges and the sales associated said I was "in good shape."

The next day I decided to try it again. Repetition is the key to good science so why not try to be a bit more scientific about it. Now I suddenly weighed 179.8 lbs, but to my surprise my body fat had dropped to 7.8% overnight and my body water was now at 60.2%. I was happy to learn that I had gained nearly 22lbs in muscle mass by lying around, and happy but puzzled that my physique was now rated 8 or "thin and muscular." Not entirely surprising my basal metabolism had increased to 2,153 cals and my metabolic age dropped to 12. My bone mass was up to 8.2 lbs, but my visceral fat was unchanged.

Finally on the day before my race, day 3, I decided to go see my friends at Tanita again. I was delighted to learn that my weight was now down to 176 lbs, but unfortunately, my body fat had gone back up to 16.6%. With my body water at 55.7%, the sales associate now thought 55.7 was too low and the results might be inaccurate. The first day associate never mentioned any of this.

In any case, this new guy estimates my body fat is more like 12%. Even so, my muscle mass has shrunk back to 140 and I am again "very muscular." My metabolic age is at 12, but my visceral fat rating has dropped to 3 overnight.

Intrigued I went home and bought a body composition scale. Since I was not willing to drop $130 for a Tanita I got a cheap Taylor that was on sale for less than $30 at the local supermarket. If nothing else I could use it to weigh myself and estimate my fluid losses. The Taylor only spits out weight and % body fat. It also does not sport the coveted m-dot logo or an "athlete mode." The lack of these important features explains the $100 price difference.

Not as fancy

My Taylor was more consistent -probably because the environment in my bathroom is more consistent- but it stubbornly insisted my body fat was between 18-20%. The lowest reading I ever got was 16%. That was until I discovered a simple trick. One day I mistyped my age and to my surprise, my body fat dropped by half. It turned out age is the main determinant of the body fat estimate. That tells me the Taylor (and likely the Tanita) use a simple lookup table. For a given impedance measurement -the scale sends a current through the body and measures the complex resistance known as impedance- the scale returns a number based on your age. If I drop my age to 25, my body fat miraculously drops to 10%.

Since then I just use the scale to check my weight.

A little while later, at the Napa marathon, Kaiser Permanente offered a free body fat measurement. This was done by a nurse using an electrical device on the arm. The measurements came out as follows: weight 170lbs, body fat 7.9% and hydration 58. The Kaiser people did two independent measurements (a very good sign) and averaged the results before telling me what they were. They also did not ask for my age until after they gave me results.

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