## Bodyfat Explained

This info about bodyfat comes from the ACSM text, (American College of Sports Medicine), Resource Manual for Guidelines for Exercise Testing and Prescription, considered the gold standard when referring to Physiological testing protocol. I last read the text in 1995, so it was a good review.

First off, we are testing Body Composition, and estimating Bodyfat. “Whatever the technique, the measurement obtained is that of body density, (density of either lean body mass or fat mass). Density is the measure of compactness and it is known that the density of fat and muscle and the ratios of skeletal weight and body water to lean body weight are extremely constant. Density is equal to the mass divided by the volume.” The formula we use takes seven pertinent skinfold site measurements, calculates Body Density, and then gets put into another formula that comes up with ‘estimated’ Bodyfat. FYI: 50% of our fat is subcutaneous, (under the surface of the skin), and the other 50% is viceral, (around, within, and comprising organs & tissue). Some people more, some people less. This is why a formula had to be devised to predict based on populous research. There is no way to accurately measure true BF, and there never will. you can’t even get to 50% of it.

“Skinfold thickness is the most practical technique for estimating bodyfat. This technique relies on the observation that, within any population, a certain fraction of the total body fat lies just under the skin and if one could obtain a representative sample of that fat, overall body fatness, (density), could be predicted. Investigators have found that the subcutaneous fat represented a variable fraction of total fat (20-70%) depending on age, sex, overall fatness. Generalized equations have been developed for predicting bodyfat by Jackson & Pollock. The equations have been cross-validated with independent samples and can be used in the generalized popualtion of the US. These equations have been developed using regression models that take into consideration data from several different research studies, the main advantage being that one generalized equation can be substituted for several population-specific equations without a loss in prediction accuracy for a wide range of individuals.”

The reason age factors into the formula, (your original question and doubting), is that the researches Jackson & Pollock took 600 people all different races, ages, (20-60yrs), genders, fit & unfit, athletic & non-athletic, large & small people, with proportions equal to the American population and devised the formula that correlates with their results to estimate bodyfat on others. Age and gender are factored into the formula, but not race, I guess that was not a significant coefficient to matter. There is no way to perfectly assess bodyfat, not even water. It has a margin of error of +or-2.5%, skinfold method +or- 3.7%. “The most direct way to measure body composition is to do a chemical analysis of the whole body to determine the amount of water, fat, protein, and minerals.” AKA Dead.

Just to let you know how little age does impact the result of this equation, in the case of your body fat, (at current calculation of 59.5mm skinfold thickness), putting in age 48 yields 11.22%, age 52: 11.67%, age 45: 10.96%, age 55: 12.01%. The skinfolds are what are important and why they are plugged in twice.

The formula the devised is pretty darn accurate, comes down to tester accuracy, and is accepted worldwide as being the most practical and accurate. They have been recently doing bodyfat via MRI, but again they only assess the abdomen, still not accurate.

What about the guy with chubby fingers or the lady with ‘Cankles’? So at the end of the day it is just that, an estimate, we do the best that we can and heck, if it goes down, using the same tester for reliability, it goes down…all is good.