A Closer Look At Skinfold Assessment
Skinfold analysis is a common field assessment used by fitness professionals to predict body fatness. The technique is based on the fact that 50-70% of stored fat lies between the skin and muscle, referred to as subcutaneous fat. The measurement technique requires the tester to identify gender specific sites which reflect predetermined assessment locations for regression equations calculated to predict body density. Two of the most popular groups of equations identified by their respective name sake are the Jackson & Pollack, and Durnin & Wormersley multi-site skinfold equations. The equations are based on the measure of skinfold at select sites expressed in millimeters of thickness. The skinfold measurements are entered into the population specific regression equation to predict body density which is expressed as a percentage of fat. According to the literature, use of field method prediction equations developed from 2-component model (Siri equation) reference measures of body composition systematically underestimate relative body fatness based on comparisons to hydrostatic (underwater) weighing. Ethnic differences further invalidate the Siri equation as seen in American Indian women, African-American men and women, and Hispanic women when standard equations are used. Researchers suggest that this is due to the fact the average fat free body (FFB) density of these ethnic groups exceeds the assumed value (1.1 g/ml). Unfortunately, the overwhelming majority of field method prediction equations have been developed and cross-validated for Caucasian populations and are based on 2-component model reference measures. Because ethnicity may affect the FFB and regional fat distribution, race-specific prediction equations should be used to enhance the accuracy of the assessment.