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Whether you are trying a new gainer diet, cutting up, or just curious, it's often a good idea to get a bodyfat measurement done. There are various methods in use, and some are far better than others. In order of decreasing accuracy:
Extremely accurate. The physician seperates your fat from other tissues and weighs everything. Fairly inconvenient, as it requires you to be dead.
- Hydrostatic Weighing ("Dunk Tank")
Requires the individual to expel all their air underwater. Expensive and difficult to locate a suitable facility.
- Skinfold Measurements
By far the most common method and is generally accurate to within a few percentage points. Cheap (usually about $5 to get the test done at a reputable fitness center). More detail on this method, below.
- Bioelectrical Impedance (BIA)
These devices pass a small current between either your hands or feet and determine the effective resistance. From this, and a host of assumptions about the conductivities of various body tissues, they try to determine the percentage of body fat. Some bathroom scales even include this ability but one should be very skeptical of the unit's accuracy. Some people have reported wildly-varying results with these, although some manufacturers claim high correlations with skinfold or underwater weighing results. Very dependant upon your state of hydration.
- Infra-red (IR)
Infra-red measurements are made at your finger, and through some magic, they attempt to determine your body fat composition. Very inaccurate, but convenient and fast.
- Generalized Formulae (waist, height, weight)
Numerous studies into the anthropometry of various individuals have been compiled into tables that include the person's weight, height, waist and actual bodyfat (generally done via skinfold measurements). A simple linear prediction formula is then created that fits loosely to the average population. These are very easy to use, and cost you nothing, but they should only serve as a very rough estimate. A section below details a few of these formulae.
A number of formulae have been proposed for bodyfat estimation from sum of skinfolds (SOS), but only two are often used:
- Durnin & Womersely (DW)
- Jackson & Pollack (JP)
It seems that the JP equations give slightly more accurate estimates than the DW equations for your average trainer. The JP equations are actually of two varieties, one is a 3-site test, the other a 7-site test. For individuals with low bodyfats, it is best that the 7-site test be used. In general, the locations for the 7 skinfolds are taken as follows:
The actual regression equation for the 7-site JP can probably be found in the British Journal of Nutrition 40:497, 1978. Jackson & Pollack.
It should be noted that although the formulae are available, one should get the actual computation done by a reputable facility (with a computer). There, you should always attempt to get the same person to perform the test, as the results vary significantly from tester to tester. These differences are generally from the exact location of the sites and the way they grab the skinfolds. Thus, with different people making the measurements, you will likely see fluctuations that may not be there.
Your best bet is to get periodic measurements done at a good facility (say, once every 2 months), but then log your own skinfold measurements every 2 weeks. What is important is not the actual bodyfat estimate percentage, rather it is the *change* in skinfold measurements or percentage. If you see a gradual increase in your abdominal skinfold measurement (over time), then you can safely assume that you are putting on fat. Don't measure too frequently, as these measurements could vary enough that the fluctuations due to state of hydration, etc. will outweigh any actual changes in bodyfat.
One should also be aware that it is generally not possible to do these skinfold measurements yourself. Some of them require positioning that would be very difficult (eg. subscapular). So, if you are going to do your own logging of skinfolds, get a friend to do it for you each time. To do it properly, one must use a skinfold caliper, not a ruler, and know how to isolate the fat thickness. There is a specified caliper squeezing force that is used to standardize the measurements (the tester will squeeze the caliper until it 'clicks'), and you will not be able to accurately assess this force with a ruler. Skinfold calipers are expensive, so a ruler may have to suffice (for purposes of general fluctuation estimates).
- For men: Bodyfat = -98.42 + 4.15*waist - .082*bodyweight
- For women: Bodyfat = -76.76 + 4.15*waist - 0.082*bodyweight
- NOTE: "waist" is in inches, "bodyweight" is in pounds.
- Both formulae will give you the total number of pounds of bodyfat, not your percentage. To get your percentage, divide the result above by your total body weight.
This method is based on three skinfold measurements. All skinfold measurements should be taken on the right side. Use the following 3 measurements:
- Chest: Measure a diagonal fold on the outside of the pectoral muscle, halfway between the nipple and shoulder crease. The fold should be parallel to the outside edge of the pectoral muscle.
- Abdomen: Measure a vertical fold one inch to the right of the belly button.
- Thigh: Measure a vertical fold at the middle of the front thigh.
Measure when the skin is dry, before exercise, and when you're not overheated. Measure each skinfold 3 times and use the 2 which agree--pinch from the top, measure from the bottom. The standard caliper measures in millimeters, so if yours measures in inches, you'll need to convert the numbers before going on (1 inch=25.4 mm).
Now the math. The sum of these 3 measurements (in mm.) is first used with the person's age to calculate body density in a quadratic equation.
Body Density = (1.1093800 - (0.0008267 * (Sum of 3))) + (0.0000016 * (Sum of 3 * Sum of 3)) - (0.0002574 * (Age))
Percentage Bodyfat is then calculated with the following formula:
% Bodyfat = (((4.95 / Body Density) - 4.50) * 100)
Reference: Practical Assessment of Body Composition, A. S. Jackson and M.L. Pollack. The Physician & Sports Medicine, Vol. 13, No. 5, May 1985.
Thanks to m.f.w. post from Jeff Amason (email@example.com):
The equation I use is from Parillo's Bodystat Maunal. I use Slim Guide calipers and do a 9 point measurement:
- Upper pec (horizontal fold)
- Subscapular (vertical fold)
- Bicep (vertical fold)
- Inside tricep (horizontal fold)
- Kidney (horizontal fold)
- Suprailliac (horizontal fold)
- Abdominals (vertical fold)
- Mid quad (vertical fold)
- Inside calf (vertical fold)
Total all measurements and divide by your body weight. Multiply this total by 0.27. This will be your % body fat.