Skinfold Measurements
by: Lyle McDonald
The sites are as follows: All measurements are taken on the right side regardless of what hand you use to write.
Pec : a diagnoal fold taken 1/2 between the nipple and the upper portion of the pec. Women should take this skinfold 1/3 the distance between the upper portion of the pec and the nipple (higher than what I've got shown)
Suprailiac : a diagonal fold taken above the superior anterior iliac crest.
Abdominals : a vertical skinfold taken 1" to the right of the belly button.
Thigh: a vertical skinfold taken 1/2 the distance between the patella and the inguinal crease (the fold you get between thigh and groin when you lift your leg).
Tricep (I drew the proper site on the bicep but just move around to the back): horzintal skinfold taken 1/2 the distance between the acromion process (pointy bone in shoulder) and olecranon process (elbow).
Other sites are:
Subscapular
Midaxillary
Biceps
Inner calf
The equations are as follows :
For women:
Body density = 1.099421 - (0.0009929* X3) + (0.0000023 * X3^2) - ( 0.0001392 * X4)
Where
X3 = sum of triceps, suprailiac, and thigh skinfolds.
X3^2 = sum of 3 skinfolds squared
X4 = age in years
Watch all those zeros.
now, to convert body density into bodyfat %, use:
BF% = (457/body density) - 414.2
For men:
Body density = 1.1093800 - (0.0008267 * X3) + (0.0000016 * X3^2) - (0.0002574 * X4)
Where:
X3 = sum of chest, abdomen, and thigh skinfolds
X3 ^ 2 = sum of 3 skinfolds squared
X4 = age in years
now, to convert body density into bodyfat %, use:
BF% = (495/body density) -450
Proper measurement technique
Measuring skinfolds accurately takes a lot of practice. Some have estimated that at least 100 measurements are necessary before skill is adequately developed.
To measure the skinfold, you must get a parallel fold of flesh between your fingertips and lift it off the muscles. Typically, you lift the skinfold with your left hand and calipers go in your right (so you can read the numbers).
After you lift the skinfold, put the caliper tips about 1" above your fingerips and release the trigger. Wait 2 seconds and take your reading. You should release the skinfold between measurements to avoid pushing water out of the skinfold and getting progressivel lower measurements. Ideally, you should rotate sites. For example, for me, you should really measure
pec, abs thigh pec abs thigh pec abs thigh
You have to pinch fairly hard with your fingers. A fellow trainer said it best "If they don't yelp when you pinch the skinfold with your fingers, you didn't pinch hard enough." (Sounds like a personal kink to me).
You should take a minimum of 3 measurements and at least 2 of them should be within 1-2mm of each other for accuracy.
And, keep in mind that the equations are only accurate within a narrow range. Just go by total skinfolds and you'll be fine. If total skinfold counts are going down, you're losing bodyfat.
FWIW, the Canadian Associaton of Sports Science (who does extensive sports science testing of it's athletes) has done away with prediction equations completely. They simply use changes in skinfold as a way to measure changes in body composition (3).
References:
1. "Practical Assessment of Body Composition" Andrew S. Jackson and Michael J. Pollock. Physician and Sports Medicine Vol 13(5): 76-90
2. "Guidelines for Exercise Testing and Prescription" American College of Sports Medicine. Lea and Febiger Publishers, 4th edition 1991.
3. "Physiological Testing of the High-Performance Athletes" JDuncan MacDougall et. al. Human Kinetics Publishers, 1990.