Making Sense of Measurements
When you’re trying to get into better shape, your primary goal is to lose fat. While many people describe this as “losing weight” they’re not the same thing at all. Your overall weight is a combination of your lean body mass (organs, muscles, and bones), adipose tissue (fat), hydration (how much water you have in you), and any food currently in the process of digestion or waste disposal. Saying that you “lost 10lbs” could mean a number of different things, depending on where those pounds came from. For example someone with a cast on both legs could easily lose quite a bit of muscle mass due to atrophy, yet this is not a positive result from a weight management standpoint.
You two best tools when tracking your progress are the weight scale, which everyone is pretty familiar with, and the bodyfat tester which measures your bodyfat as a percentage of your overall weight. Measuring hydration and current food in process is pretty difficult, and results in quite a bit of confusion about your current weight, since it can vary your totals by as much as 5lbs either way on a daily basis. Since there is so much built in error it’s difficult to see what the actual results are when you’re dieting.
The solution to this problem comes from the stock market, where daily prices can fluctuate wildly, but traders still need to be able to see trends. What they do is use a moving average, so that the average price is updated daily. Here are the closing prices for Microsoft for the last five days:
11/29 33.59
11/30 33.60
12/03 32.92
12/04 32.77
12/05 34.15
If we were going to use a three day moving average it would look like this:
11/29 33.59 = 33.59
11/30 (33.60 + 33.59) / 2 = 33.595
12/03 (32.92 + 33.60 + 33.59) / 3 = 33.37
12/04 (32.77 + 32.92 + 33.60) / 3 = 33.09
12/05 (34.15 + 32.77 + 32.92) / 3 = 33.28
As you can see each day the oldest price is dropped and the newest is added. Normally traders use a longer moving average, say fourteen days or so, to see trends. With modern spreadsheets, this is actually very easy to do, and the computer does all the heavy math for you. So why is this important? Well since your daily weight and bodyfat numbers aren’t that reliable you can use a moving average to help you see the trend values. I’ve found that the best kind of moving average for this sort of thing is called a “10% smoothed exponential moving average”, as recommended by John Walker, inventor of AutoCad, and writer of “The Hacker’s Diet”. His work was very influential in helping to shape my thoughts on weight loss, though there has been considerable progress in terms of understanding fitness and nutrition since his original document was written.
Each morning you should weigh yourself and take a bodyfat % reading (using calipers or an impedance unit), and note the results in a spreadsheet. Then the program will automatically make pretty graphs for you, and you can even tell it to put in a linear regression line which will show you the overall trend and slope (rate of progress). This sort of exact information is very useful in terms of feedback. You’ll be able to see your exact calorie deficit and the results of any modifications you make to your diet will show up very clearly on the graph.
Tags: Engineering, Tracking