Physical Education · Ch 6 — Test, Measurement & Evaluation
Skinfold Measures (3-Site)
Skinfold Measures (3-Site)
While BMI and WHR work from simple body dimensions, the skinfold measurement gets closer to the real quantity of interest - the amount of fat stored just under the skin - and uses it to estimate the body-fat percentage. It is a widely used field method because it is quick, portable and far cheaper than laboratory techniques such as hydrostatic weighing, BIA or DXA.
What a skinfold is
A skinfold is a double layer of skin plus the underlying fatty (subcutaneous) tissue. A large part of the body's fat lies directly beneath the skin, so if a fold of skin is pinched and lifted away from the muscle, the thickness of that fold indirectly indicates how much fat is stored at that site - the more fat, the thicker the fold.
The instrument - the skinfold caliper
The measurement is taken with a standard skinfold caliper, a spring-loaded pincer that applies a standard, constant pressure of 10 gm per mm^2 to the fold and reads its thickness in millimetres. The constant pressure matters because fatty tissue is compressible - standardising it keeps readings comparable. A number of calipers exist, but the most reliable are the Harpenden, Lange and Lafayette skinfold calipers.
How a measurement is taken
- Pinch - with the thumb, forefinger and middle finger of the left hand, grasp and lift a fold of skin and its underlying fat away from the muscle, at a pre-marked site.
- Place the caliper - apply the caliper jaws about half a centimetre below the picked fold, at the pre-marked level, so the caliper measures the fold and not the fingers.
- Read - release the full pressure onto the fold and read the thickness about 2 seconds after releasing the pressure, recording it in millimetres.
- Repeat and average - take the reading more than once at each site and use the average, to reduce error.
Consistency matters: use the same sites, the same side of the body, the same technique and ideally the same tester each time.
Three standard sites
The syllabus prescribes a 3-site protocol: skinfold thickness is measured at three standard body sites, and the set of sites typically differs for males and females, because the sexes deposit subcutaneous fat in different patterns.
Different standard protocols specify different site triples and different equations, and the CBSE syllabus does not fix one uniformly. This section therefore teaches the procedure and principle and deliberately does not prescribe a specific set of three sites or a particular regression equation - learn how the measurement is done and why.