Bioimpedance analysis (BIA) has been demanded for the assessment of appendicular skeletal muscle mass (ASM) in clinical and epidemiological settings. This study aimed to validate BIA equations for predicting ASM in the standing and supine positions; externally to cross-validate the new and published and built-in BIA equations for group and individual predictive accuracy; and to assess the overall agreement between the measured and predicted ASM index as sarcopenia diagnosis. In total, 199 healthy older adults completed the measurements of multifrequency BIA (InBody770 and InBodyS10) and dual-energy X-ray absorptiometry (DXA). Multiple regression analysis was used to validate the new multifrequency bioelectrical impedance analysis (MF-BIA) prediction equations. Each MF-BIA equation in the standing and supine position developed in the entire group included height²/resistance, sex, and reactance as predictors (R² = 92.7% and 92.8%, SEE = 1.02 kg and 1.01 kg ASM for the standing and supine MF-BIA). The new MF-BIA equations had a specificity positive predictive value and negative predictive value of 85% or more except for a sensitivity of about 60.0%. The new standing and supine MF-BIA prediction equation are useful for epidemiological and field settings as well as a clinical diagnosis of sarcopenia. Future research is needed to improve the sensitivity of diagnosis of sarcopenia using MF-BIA.

This study examined how the structure of friendship networks influences two risk behaviours in tandem (drinking and sexual intercourse) among a sample of US adolescents (7th–12th grades, n = 901; 2 schools) from Wave I of the Add Health data. For one school, adolescents in denser and smaller networks were at higher risk for engaging in sexual intercourse and drinking alcohol simultaneously. In that school, network attributes (out-degree and betweenness) and adolescents’ age were associated with an increased risk. In the other school, more diffused friendship networks posed less risk of engaging in these two behaviours in tandem. Moreover, engagement in risky behaviours was significantly predicted by teens’ age and gender. We conclude that friendships’ influence on adolescents’ risk behaviours varies, depending on size and composition of the networks and adolescents’ characteristics. Moreover, understanding adolescents’ social ties can be useful for health promoters, thus research on adolescent networks remains warranted.