Associations Between Muscle Thickness, Motor Function, and Echo Intensity in Community-Dwelling Older Japanese Men and Women

Purpose Muscle atrophy progresses with age. The motor function may be estimated by measuring the muscle mass; however, if muscle quality deteriorates due to an increase in connective tissue within the muscle, a decline in motor function may be missed by measuring muscle mass alone. Therefore, it is important to understand the relationship between muscle mass, muscle quality, and motor function. This study aimed to clarify how changes in muscle thickness, measured using ultrasound imaging, in older people are related to motor function and echo intensity. Patients and methods The thickness and echo intensity of the four quadriceps muscles were measured using an ultrasound imaging device in 110 community-dwelling older individuals. Correlations between muscle thickness, motor functions such as walking and muscle strength, and echo intensity were analyzed in each sex. Partial correlation analysis was conducted using age as a control variable. Results A significant correlation was observed between muscle thickness and motor function in both men and women. There was no significant negative correlation between muscle thickness and echo intensity of the same muscle in men, except between each muscle thickness and the vastus medialis (p < 0.001 or p = 0.007), between the sum of the four muscle thicknesses and vastus medialis thickness (p = 0.02), and between the vastus medialis thickness and echo intensity (p < 0.006). In women, a significant correlation was observed for all muscles. Partial correlation analysis revealed a similarly significant correlation between muscle thickness and echo intensity in men and women. Conclusion We observed sex differences in the relationship between muscle thickness and echo intensity. This suggests that, even after adjusting for age-related factors, women may show more pronounced changes in muscle quality than men, with increased echo intensity due to increased intramuscular connective tissue with muscle atrophy.