The purpose of this study was to develop a multi‐site near‐infrared (NIR) model (Model I) and compare its predictive accuracy to single‐site models (IIA and IIB). In Model I, the sum of two optical density (OD) measures (Σ2OD), age, body weight, height, and physical activity level were used as potential predictors of body density (Db). In Model IIA, the variables used in the manufacturer's NIR equation (biceps OD1 and OD2, body weight, height, gender, and physical activity level) were the potential predictors. This model was modified by including age as an additional potential predictor in Model IIB. We also examined the test‐retest reliability and interrelationships of OD measures taken at 10 anatomical sites, as well as the validity of the manufacturer's NIR equation, for estimating body composition of women. The subjects, 148 women between 20 and 72 years, were hydrostatically weighed to determine criterion Db. The Futrex‐5000 was used to measure OD1 and OD2 at 10 anatomical sites. Only two sites (pectoral OD2 and biceps OD2) contributed significantly to the variance in Db. Thus, the sum of these two ODs (Σ2OD), was used as a potential predictor in the multi‐site model. Test‐retest reliability was high, with intraclass correlation coefficients ≥0.85 for many of the OD measurements. Intercorrelations of ODs ranged from 0.22 to 0.91. In the multi‐site model (I), ΣOD, body weight, age, and height were significant predictors, accounting for 85.7% of the variance in Db. The SEE was 0.0076 g/ml or 3.3% BF. In the manufacturer's model (IIA), biceps OD2, body weight, and height accounted for 76.3% of the variance in Db, and the SEE was 0.0094 g/ml (4.1% BF). When age was included as a predictor (Model IIB), the R2 increased (86.0%) and the SEE (0.0073 g/ml or 3.1% BF) decreased substantially. Cross‐validation of the three equations yielded r2s ranging between 0.688 (Model IIA) and 0.748 (Model I) and slightly larger SEEs (0.0094–0.001048 g/ml). There were no significant differences between average criterion Db and predicted Db for each equation. The manufacturer's equation programmed in the Futrex‐5000 yielded a lower r2 (0.55), higher SEE (5.61% BF), and significantly underestimated criterion % BF by an average of 3% BF. Either the multi‐site (model I) or single‐site (Model IIB) equations is recommended to estimate body composition of this population. © 1992 Wiley‐Liss, Inc.
ASJC Scopus subject areas
- Ecology, Evolution, Behavior and Systematics