Background: The skeletal muscle echo intensity (EI) during ultrasound imaging has been investigated to evaluate the muscle quality. However, EI fluctuates according to the scanning conditions.Methods: The motor functions and ultrasound images of 19 elderly (73±3.2 years) and 19 young (22±1.5 years) individuals were investigated and an EI frequency component was assessed for more reliable evaluations. Healthy elderly and young subjects participated in this study. The motor functions were assessed during walking and according to the knee extension muscle strength. The muscle thicknesses of rectus femoris (RF), vastus intermedius (VI), and quadriceps femoris (QF) were investigated. EIs were calculated and the mean frequencies of the regions of interest (MFROIs) for RF and VI were analyzed. Results: EIs and MFROIs were greater in elderly subjects than in young subjects (P<0.01 for RF, and P<0.001 for VI, in EIs; and P<0.01 for RF, and P<0.05 for VI, in MFROIs). In young subjects, EI of RF was greater than that of VI; however, there was no difference between the RF and VI MFROIs in both elderly and young subjects. EIs of VI exhibited a significantly negative correlation with the QF thickness in both elderly and young subjects. RF MFROIs negatively correlated with the QF thickness and positively correlated with EI of VI in elderly subjects alone. Conclusion: These findings suggest that MFROIs of elderly individuals would have a larger value than those of young individuals; moreover, MFROIs did not fluctuate greatly with the tissue depth and scanning conditions. MFROIs might be thus useful for further investigations of muscle quality and applications for the early prevention of age-related motor functional decline.
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