Skinfold Measures

Skinfold Measures

Skinfold thickness provides a good measure of subcutaneous fat.

Because there is a relationship between subcutaneous fat and total fat, the sum of several skinfold measures can be used to estimate total body fat.

Skinfold Measures

Skinfolds include skin and SAT, the latter consisting of adipocytes that contain triglycerides and connective tissue that includes blood vessels and nerves.

Skinfold Measures

The thickness of a double layer of skin is about 1.8 mm, but this varies among individuals and systematically by site and with age.

Skinfold Measures

Variations in skin thickness among individuals affect the validity of skinfold thickness as measures of subcutaneous adipose tissue (SAT).

Skinfold Measures

The paucity of SAT in the lean can make it difficult to elevate a fold, and it is not easy to elevate folds with parallel sides in those with large amounts of SAT.

Skinfold Measures

Skinfold thicknesses are less precise than circumferences in overweight individuals than in general populations, but skinfolds are less affected by edema than circumferences because caliper pressure reduces the fluid content of SAT.

Skinfold Measures

Skinfold thicknesses are affected by individual and regional differences in compressibility that vary with age, gender, and recent weight loss.

Skinfold Measures

When a skinfold thickness is measured, the pressure exerted by the calipers displaces some extracellular fluid.

Skinfold Measures

In addition, pressure from skinfold calipers may force some adipose tissue lobules to slide into areas of lesser pressure; – this sliding may be more marked for thick

skinfolds in which the adipose tissue contains little connective tissue.

Skinfold Measures

Factors to be considered in the selection of skinfold sites for screening, or for possible inclusion in predictive equations, include

• accessibility in relation to undressing,• precision, • the availability of reference data, • and the thickness of the fold, which is important

in overweight subjects.

Skinfold Measures

It may be impossible to measure skinfold thickness at some sites in overweight subjects because the thickness may exceed the maximum jaw openings of the calipers.

Skinfold Measures

As an alternative, measurements can be made at sites where there is little SAT (e.g., biceps),

or ultrasound can be used to measure SAT thickness,

but there are few reference data for unusual sites or for ultrasound values and few predictive equations based on them.

Skinfold Measures

Skinfold thicknesses have low correlations with FFM (about 0.2),

but they are highly correlated with % BF (r = 0.7 to 0.9)

and these correlations do not differ markedly among the common sites.

Skinfold Measures

Despite the relatively high correlation between skinfold thicknesses at single sites and % BF, no one skinfold thickness is an accurate predictor of % BF.

Skinfold Measures

This reflects individual variation in the distribution of SAT and in the proportion of the total adipose tissue that is subcutaneous.

Skinfold Measures

There are gender- and age-differences in the relationships of skinfold thicknesses to % BF.– Only three or four skinfold thicknesses are

needed in predictive equations.

Skinfold Measures

In children, skinfold thicknesses are better predictors of body density than are circumferences.

Skinfold Measures

The use of skinfold thicknesses to predict % BF from densiometry is based on implicit assumptions that:– measurements of skinfold thicknesses at a

few sites provide an adequate description of SAT

– there is a fixed relationship between SAT and DAT.

Skinfold Measures

The first assumption appears correct since there are generally high correlations between skinfold thicknesses at different sites, but there are age and gender differences in the relationships between SAT and DAT.

Skinfold Measures

Specific predictive equations are needed for children and adolescents because the distribution of adipose tissue and body composition proportions (e.g., leg length/stature) differs between children and adults.

Skinfold Measures

The Jackson and Pollock equation to predict BD for young men was developed from a group that was slightly taller and lighter than U.S. national data.

Skinfold Measures

The equation of Jackson et al. to predict body density for young women, which was developed from a group slightly taller and lighter than U.S. national data, had a RMSE of 0.0086 g/cc which was equivalent to 3.9% and a PE equivalent to 3.7%.

Skinfold Measures

Skinfold equations derived from young adults commonly underpredict % BF in the middle-aged and elderly, perhaps because of changes with age in the density of FFM and in the relationship between SAT and DAT, including increases in the fat content of muscles.

Skinfold Measures

Vu Tran and Weltman reported an equation to predict % BF in middle-aged men.

The equation was based on circumferences and had a RMSE of 3.6% and a PE of 4.4% on cross-validation.

Skinfold Measures

In the obese, the proportion of total adipose tissue that is subcutaneous may be lower than in general populations and extracellular fluid is increased.

Skinfold Measures

Therefore, equations are needed that are specific for the obese.

There is evidence that these equations should be based on circumferences rather than skinfold thicknesses.

Skinfold Measures

Teran developed an equation to predict % BF calculated from body density using a two-component model in obese women aged 18 to 50 years.– The RMSE was 4.2% BF and the PE was

3.9% BF on cross-validation.

Skinfold Measures

Equations to predict % BF calculated from body density with a two-component model may be inaccurate in some ethnic groups because of differences from the general population in the density of FFM and in body proportions.

Skinfold Measures

Ethnic differences in the distribution of SAT indicate that skinfold equations are likely to perform poorly when applied to ethnic groups other than those from which they are derived.

Skinfold Measures

Such considerations have led to the development of equations that are specific for ethnic groups.

Skinfold Measures

Summary: predicted values are less accurate than

observed (calculated) values a predictive equation should not be

applied to a group that is markedly different from the group used to develop the equation.

Skinfold Measures

Important group differences may relate to age, gender, ethnicity, and level of body fatness.