Ultrasonographic Size of the Thenar Muscles of the Nondominant Hand Correlates with Total Body Lean Mass in Healthy Subjects

Sarcopenia is associated with adverse outcomes in clinical situations such as elderly population, in-hospital setting and oncologic patients. However, no direct measurement of muscular mass is routinely available for clinicians. The aim of this study was to assess the correlation between thenar musculature of the nondominant hand evaluated by ultrasound and body fat-free mass. In this one-center, cross-sectional, observational study, the width and depth of thenar muscles of both hands was assessed by ultrasonography. Nondominant hand musculature was taken as reference as a better estimator of total body muscular mass. These data were compared to body composition by bioimpedance analysis and dual-energy X-ray absorptiometry (DXA), hand grip strength, arm muscular area and physical activity (with International Physical Activity Questionnaire ). Statistical correlation was determined for each parameter. We obtained ultrasonographic measurements, International Physical Activity Questionnaire and hand grip strength from 83 subjects, whereas bioimpedance was performed in 64 subjects and DXA in 29 subjects. The strongest correlations were found between longitudinal thenar depth vs fat-free mass index (fat-free mass in DXA [kg]/height2 [m]) (r = 0.63, p < 0.001, 95%CI 0.34–0.81), longitudinal depth and hand dynamometry (r = 0.72, p < 0.001, 95%CI 0.59–0.81), longitudinal depth and DXA fat-free total mass (r = 0.76, p < 0.001, 95%CI 0.54–0.88), transversal thenar depth vs fat-free mass index (r = 0.67, p < 0.001, 95%CI 0.41–0.83), transversal width and DXA fat-free total mass (r = 0.62, p < 0.001, 95%CI 0.33–0.8), transversal depth and DXA nonfat total mass (r = 0.81, p < 0.001, 95%CI 0.63–0.91). Ultrasonographic examination of the nondominant thenar musculature is a fast and simple way of assessing total body fat-free mass, showing a good correlation with body composition measured by bioimpedance analysis and DXA, hand grip strength and arm muscular area.