[Purpose] This study aimed 1) to assess whether a prediction model for whole body skeletal muscle mass that is based on a sedentary population is applicable to young male athletes, and 2) to develop a new skeletal muscle mass prediction model for young male athletes. [Subjects and Methods] The skeletal muscle mass of 61 male athletes was measured using magnetic resonance imaging (MRI) and estimated using a previous prediction model (Sanada et al., 2006) with B-mode ultrasonography. The prediction model was not suitable for young male athletes, as a significant difference was observed between the means of the estimated and MRI-measured skeletal muscle mass. Next, the same subjects were randomly assigned to a development or validation group, and a new model specifically relevant to young male athletes was developed based on MRI and ultrasound data obtained from the development group. [Results] A strong correlation was observed between the skeletal muscle mass estimated by the new model and the MRI-measured skeletal muscle mass (r=0.96) in the validation group, without significant difference between their means. No bias was found in the new model using Bland-Altman analysis (r=-0.25). [Conclusion] These results validate the new model and suggest that ultrasonography is a reliable method for measuring skeletal muscle mass in young male athletes.
