In ExPhysiology

January 01, 2007

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In last month's CrossFit Journal, I explained why you shouldn't pay for expensive tests such as gas analysis to measure your VO2 max. Simple tests repeated often will show your improvement (or decline) and how steep the trend curve is. Expensive tests can be accurate, but if you want to know how your fitness is progressing, an expensive test, measuring one component of fitness once per year, isn't going to give you that information. The most common request I get from students, athletes, and the general public is to measure percent body fat. Most people get the same reply I give regarding a gas analysis for VO 2 max: "Save your money."

However, the reasons behind that same reply are not identical. There are two main reasons I do not like to measure someone's percent body fat:
1. I can't do it very accurately and neither can anyone else (despite their sales pitches).
2. It is not a component of fitness and is more than likely not a causative factor in poor health (despite what the media and medical literature say).

If you get a body composition test done and you are told your percent body fat is, for example, "12%," you are being given only part of the results. The accurate information would be something like "12% body fat with a standard error of estimate of 3%." What that means is that approximately two-thirds of the people getting this result would actually be between 9% and 15% body fat. The other third would be outside this range.

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