Body Fat Percentage 3 Site Skinfold Test

How does this body fat percentage 3 site skinfold test work?

This health tool estimates the amount of fat present in the body, in percentage and as fat mass, the lean body mass and body density. These are all extracted from three measurements of skinfolds, performed with an instrument called caliper. These measurements are the input in gender specific formulas devised by Jackson and Pollock.

The first fields in the body fat percentage 3 site skinfold test are:

■ Gender – necessary because the formulas differ by gender.

■ Age – the age of the subject is taken into account in the calculation.

■ Weight – this is used to determine the body fat mass and the lean mass and can be input in either lbs or kg.

Depending on the selected gender, there are three skinfolds required. In the case of female subjects: thigh, triceps and suprailiac, while in the case of male subjects: chest, thigh and abdomen.

The instructions on how to perform the caliper measurement of fat are:

■ Thigh – Vertical fold on the anterior midline of the thigh, half way between the proximal border of the patella and the hip.

■ Triceps – Vertical fold on the posterior midline of the upper arm, halfway between the bony processes (shoulder and elbow). The arm should be held freely to the side of the body.

■ Suprailiac – Diagonal fold, immediately superior and in line with the angle of the iliac crest, on the anterior axillary line.

■ Chest – Diagonal fold, one half the distance for men and one third of distance for females, between anterior axillary line and nipple.

■ Abdomen – Vertical fold, 2 cm to the right side of umbilicus.

The recommendation is that all measurements are taken on the same side, usually the right side, and in case there are differences of over 1-2 mm between subsequent test results, the measurements should be repeated.

This is one of the most accurate methods for determining fat percentage out of body measurements. Jackson and Pollock devised two more formulas, one for 4 site calculation and another for 7 skinfold testing.

Similarly, there is the Durnin and Womersley 4 site calculator. Tape measurement calculation is something else and accounts for neck, waist and hip circumference, for example the US Navy tape measurement.

The main criticism received by the model is around the fact that there may be inaccuracies in measuring due to lack of preciseness (measuring the same spot every time). Some argue that callipers only measure fat deposits from under the skin and cannot provide reliable information on fat distribution through the body.

Jackson and Pollock 3 site formula

The skinfold measurements obtained with the calipers need to be input in the gender specific formulas and the intermediary result is the body density, noted D.

For females:

D = (1.0994921 - (0.0009929 x (Triceps + Thigh + Suprailiac)) + (0.0000023 x (Triceps + Thigh + Suprailiac)²) - (0.0001392 x Age))

For males:

D = (1.10938 - (0.0008267 x (Thigh + Chest + Abdomen)) + (0.0000016 x (Thigh + Chest + Abdomen)²) - (0.000257 x Age))

Body density is transformed in fat percentage with the SIRI formula:

BF% = 495/ D - 450

Body fat is obtained from the BF% and subject weight based on:

Body fat mass = BF% x Weight / 100

Lean body mass = Weight – Body fat mass

Example calculation

Taking the case of a female aged 28, weighing 146 lbs and having the following skinfold measurements:

Thigh = 24; Triceps = 18; Suprailiac = 26;

The calculation result is:

■ Body fat percentage = 26.6%;

■ Body fat mass = 38.8 lbs;

■ Lean body mass = 107.2 lbs;

■ Body density = 1.04 x 10³ kg/m³.

Because fat percentages can offer information on the fitness levels of the body, the American Council on Exercise devised the following:

References

1) Jackson AS, Pollock ML, Ward A. (1980) Generalized equations for predicting body density of women. Med Sci Sports Exerc; 12(3):175-81.

2) Jackson AS, Pollock ML. (1978) Generalized equations for predicting body density of men. Br J Nutr; 40(3):497-504.

3) Vasudev S, Mohan A, Mohan D, Farooq S, Raj D, Mohan V. (2004) Validation of body fat measurement by skinfolds and two bioelectric impedance methods with DEXA--the Chennai Urban Rural Epidemiology Study [CURES-3]. J Assoc Physicians India; 52:877-81.

4) Aristizábal JC, Restrepo MT, Amalia L. (2008) Validation by hydrodensitometry of skinfold thickness equations used for female body composition assessment. Biomedica; 28(3):404-13.