IntroductionThe association between skin-fold thicknesses in children and adolescents and elevated levels of variables considered to be indicative of risk for cardiovascular disease (CVD) in adults has been found by several investigators. '-5 In population-based studies of children and adolescents, for example, excess subcutaneous fatness has been associated with elevated blood pressure (BP),' 2,6 serum lipids, and lipoprotein fractions,2-4 and the clustering of these variables.5 Although the results of these studies demonstrate that elevated levels of CVD risk factors often accompany excess body fat in youth, the absolute level of body fat corresponding to significant risk for high BP, serum lipids, low-density lipoprotein (LDL) and very low-density lipoprotein (VLDL) cholesterols is not known.Although children and youth with triceps skinfolds 2 the 85'h percentile for age and sex are at greater risk for high BP than children with lower skinfold thicknesses,1 such a rank-ordered definition of obesity implies that the absolute level of body fatness associated with increased risk is variable. Recent work has shown that the 85th percentile may not be indicative of obesity in all samples, because skinfold thicknesses at a given percentile correspond to different levels of body fat at different ages.7,8 The 85th skinfold percentile, for example, represents fatness levels ranging from 17% to 22% in children and from 25% to 34% in adolescents.8In addition to the discrepancy between relative and absolute definitions of obesity, the triceps skinfold site has been shown to be unrelated to BP in youth when statistical adjustments were made for subscapular skinfold thickness.9Moreover, a trunkal fat pattern, independent of general body fatness, is related to high levels of LDL and VLDL and to low levels of high-density lipoprotein (HDL) cholesterol in 6-to 18-year-old youth.'0The independent effects of centripetal localization of subcutaneous fat on BP9-1" and adverse lipoprotein profiles"' make it important to control the potential confounding effect of fat patterning when the relation between total body fat and CVD risk factors in youth is evaluated.The purpose of the present study was to determine the level of body To determine the critical level of body fat associated with elevated CVD risk factor variables, the males and females were subsequently grouped by level ofpercent fat. Males were divided into the following five fatness groups: <10% (n = 217), 10% to 14.9% (n = 575), 15% to 19.9% (n = 436), 20% to 24.9% (n = 192), and >25% (n = 247). Females were grouped by body fat as follows: <20% (n = 547), 20% to 24.9% (n = 493), 25% to 29.9% (n = 313), 30% to 34.9% (n = 192), and .35% (n = 108).An index of trunk-to-limb fat distribution was computed as the natural logarithm of the subscapular/triceps skinfold thickness ratio.2-Because absolute standards for children and youth do not exist for this index of fat patterning, age-, sexand race-specific percentiles for the present sample were developed. Fat-patterning quint...

Social-ecological (SE) models are becoming more widely used in health behavior research. Applying SE models to the design of interventions is challenging because models must be tailor-made for each behavior and population, other theories need to be integrated into multi-level frameworks, and empirical research to guide model development is limited. The purpose of the present paper is to describe a SE framework that guided the intervention and measurement plans for a specific study. The trial of activity for adolescent girls (TAAG) is a multi-center study of interventions to reduce the decline of physical activity in adolescent girls. The TAAG framework incorporates operant learning theory, social cognitive theory, organizational change theory and the diffusion of innovation model in a multi-level model. The explicit and practical model developed for TAAG has already benefited the study and may have elements that can generalize to other health promotion studies.

The accuracy of total body fat mass and leg fat mass measurements by fan-beam dual-energy X-ray absorptiometry (DEXA) was assessed in 60 healthy elderly subjects (aged 70-79 yr). Total fat and leg fat mass at four leg regions (total leg, thigh, midthigh, and calf) were measured with the QDR 4500A (Hologic, Waltham, MA). The four-compartment model and multislice computed tomography scans were selected as criterion methods for total fat and leg fat mass, respectively. Total fat mass from DEXA was positively associated with fat mass from the four-compartment model with a standard error of the estimate ranging from 1.4 to 1.6 kg. DEXA fan-beam tended to overestimate fat mass for total leg and total thigh fat mass, whereas only marginal differences in fat mass measurements at the midthigh and calf were demonstrated (

The ability of dual-energy x-ray absorptiometry (DEXA) to detect small changes in body composition was studied in 17 men and women during a dehydration-rehydration protocol. Scale weight (BW) and total mass (TM) from DEXA were highly related (r > 0.99) as were estimates of fat-free mass (r = 0.99) and percent fat (r = 0.97) from DEXA and densitometry. Changes in BW of approximately 1.5 kg due to fluid loss and gain were highly correlated (r = 0.90) with both changes in TM and soft-tissue mass (STM) by DEXA but less so (r = 0.67) with changes in lean-tissue mass (LTM). Mean changes in TM, STM, and LTM were not different (P > 0.05) from changes in BW. Estimates of bone mass and fat were unaffected by changes in hydration. We conclude that DEXA is able to detect small individual changes in TM and STM and is also useful for detecting group changes in LTM.

Whole-body bioelectrical impedance analysis (BIA) was evaluated for its reliability and accuracy in estimating body composition in children. The hypothesis that the index, body height2 divided by resistance (RI), can accurately predict fat-free body mass (FFB) and percent fat (%FAT) in children was tested on 94 caucasian children 10-14 yr old. Criterion variables were FFB and %FAT estimated using multicomponent equations developed for children. BIA measurements (resistance and reactance) were found to be reliable. Prediction accuracy (standard error of the estimate, SEE) for FFB from RI alone was 2.6 kg and for %FAT from RI and body weight was 4.2%. For RI, anthropometric variables and reactance, the SEE improved to 1.9 kg FFB. For RI and anthropometric variables, the SEE was 3.3% FAT. For anthropometric variables alone, the SEE's were 2.1 kg FFB and 3.2% FAT. Adult FFB and %FAT prediction equations cross-validated with this sample resulted in SEE's similar to those for adult samples. We conclude that RI together with anthropometry is a reliable and an acceptably accurate method of estimating FFB mass and %FAT in children.