Association among measurements obtained using portable ultrasonography with sex, body mass index, and age in a large sample of adult population

Background The assessment of the site-specific distribution of subcutaneous tissues (ST) represents an important addition to the body composition (BC) estimation. In this context, ultrasound stands out as a valuable method. However, the absence of reference values complicates both the interpretation of the obtained parameters and the monitoring of their changes during nutritional interventions or training programs. Methods A total of 6,270 ultrasound images obtained with a technique using a non-diagnostic B-mode 2.5 MHz ultrasound probe (BodyMetrixTM, IntelaMetrix, Inc., Livermore, CA, USA) were obtained from adult men and women and analysed by grouping them according to sex, body mass index (BMI), and age. The thicknesses of total (tSAT), superficial (sSAT), and deep (dSAT) subcutaneous adipose tissue and muscle (MT), their ratios (sSAT/dSAT and MT/SAT), and muscle echogenicity (EG) were measured at the abdomen, thigh, chest, triceps, and hip sites. Results Women exhibited greater tSAT, sSAT, dSAT, and EG (p < 0.001) and lower MT (p < 0.001), sSAT/dSAT (p = 0.008 for the abdomen and p < 0.001 for the thigh), and MT/SAT (p < 0.001) compared to men at both the abdomen and thigh sites. SAT-related parameters showed significant correlations with BMI, with thicknesses correlating positively and ratios negatively (p < 0.001). Muscle-related parameters correlated significantly with age, with MT and EG showing positive correlations and MT/SAT showing negative correlations (p < 0.001) in both sexes. Among SAT parameters, dSAT showed the strongest association with BMI in both men and women. Conclusions This study is the first to report the mean values of SAT-related quantitative and qualitative measurements (thickness and EG) in various body sites assessed through ultrasound and their associations with sex, BMI, and age in a large cohort. These findings could prove valuable in clinical practice for precise monitoring of nutritional and/or training interventions, as well as for a more comprehensive evaluation of nutritional status.