Waist circumference is an emergent measure of body composition. Its use as a dimension of body composition is justified for various reasons. First, it is an indicator of abdominal fat as opposed to waist-to-hip circumference ratio, which is an indicator of fat distribution (Despres et al., 1989). Second, criterion measures that relate to health have already been established in certain populations of youth (Liu et al., 2010). Further, other measures are more challenging to administer, such as measuring hip circumference to determine waist-to-hip ratio (WHO, 2011). Additionally, other waist measures have insufficient data to support their consideration and have not been found to be a better predictor of health risk than waist circumference (Huxley et al., 2010). Waist circumference is strongly associated with intra-abdominal (visceral) adipose tissue (r = 0.84) and subcutaneous abdominal adipose tissue (r = 0.93) in prepupertal children (Goran and Gower, 1998) and with trunk fat (r = 0.92) in children and youth aged 3-19 (Taylor et al., 2000). On the other hand, it has been suggested that waist circumference has no advantage over BMI for diagnosing high fat mass in youth aged 9-10 (Reilly et al., 2010).
According to a measurement protocol for adolescents, intra- and interobserver technical errors of measurement for waist circumference have been calculated at 1.31 cm and 1.56 cm, respectively (Malina et al., 1973). As mentioned above, a review of reliability found higher intra- and interobserver reliability for BMI and waist circumference than for skinfold thicknesses (Artero et al., 2011). Mueller and Malina (1987) report high intra- and interobserver reliabilities for waist circumferences of 0.97 and 0.96, respectively, based on data from the Health Examination Survey for youth aged 12-17. Technical errors have also been reported in national surveys (ODPHP, 1985, 1987).
Unlike other field measures, waist circumference may not be a good indicator of percent body fat or fatness in youth. However, it is an indicator of abdominal adiposity (Lee et al., 2011), which provides information about a different dimension of body composition that is linked to health risks.
Sum of Skinfolds
Skinfolds are considered valid and reliable estimates of subcutaneous fat and predictors of percent body fat, assuming they are measured by trained individuals. Criterion-related validity for the sum of skinfold (triceps and calf) measurements ranged from r = 0.70 to 0.90 compared with hydrostatic weighing (Boileau et al., 1984). Specifically, reliability coefficients for sum of skinfolds vary by pubertal status in girls (Gutin et al., 1996). Others have reported acceptable interobserver reliability coefficients of 0.89 to 0.98 for