Applicability of ultrasonography for evaluating trunk muscles size in athletes: a study focused on baseball batters.

[Purpose] Recently, we demonstrated that the thicknesses of trunk muscles measured using ultrasonography were correlated strongly with the cross-sectional areas measured using magnetic resonance imaging in untrained subjects. To further explore the applicability of ultrasonography in the clinical setting, the present study examined the correlation between ultrasonography-measured thicknesses and magnetic resonance imaging-measured cross-sectional areas of trunk muscles in athletes with trained trunk muscles. [Subjects and Methods] The thicknesses and cross-sectional areas at total 10 sites of the bilateral sides of the upper, central, and lower parts of the rectus abdominis, abdominal wall, and multifidus lumborum in 30 male baseball batters were measured. [Results] Overall thicknesses and cross-sectional areas of the trunk muscles in baseball batters were higher than those in untrained subjects who participated in our previous study. The ultrasonography-measured thicknesses at all 10 sites of the trunk muscles correlated highly with the magnetic resonance imaging-measured cross-sectional areas in baseball batters. [Conclusion] These results suggest that the thicknesses of the trunk muscles measured using ultrasonography can be used as a surrogate marker for the cross-sectional area measured using magnetic resonance imaging, in athletes who have larger trunk muscles than that of untrained subjects.