Associations of Quadriceps Torque Properties with Muscle Size, Attenuation, and Intramuscular Adipose Tissue in Older Adults

Background: Atrophy and fatty infiltration of muscle with aging are associated with fractures and falls, however, their direct associations with muscle function are not well described. It was hypothesized that participants with lower quadriceps muscle attenuation, area, and greater intramuscular adipose tissue (IMAT) will exhibit slower rates of torque development (RTD) and lower peak knee extension torques. Methods: Data from 4,842 participants (2,041 men, 2,801 women) from the Age Gene/Environment Susceptibility Reykjavik Study (mean age 76 +/- 0.1 years) with complete thigh computed tomography and isometric knee testing. Regression models were adjusted for health, behavior, and comorbidities. Muscle attenuation was further adjusted for muscle area and IMAT; muscle area adjusted for IMAT and attenuation; and IMAT adjusted for muscle area and attenuation. Standardized betas (beta) indicate association effect sizes. Results: In the fully-adjusted models, attenuation (men beta = 0.06, 95% CI: 0.01, 0.11; women beta = 0.07, 95% CI: 0.03, 0.11) and muscle area (men beta = 0.13, 95% CI: 0.07, 0.19; women beta = 0.10, 95% CI: 0.06, 0.15) were associated with knee RTD. Attenuation (men beta = 0.12, 95% CI: 0.08, 0.16; women beta = 0.12, 95% CI: 0.09, 0.16) and muscle area (men beta = 0.38, 95% CI: 0.33, 0.43; women beta = 0.33, 95% CI: 0.29, 0.37) were associated with peak torque. Conclusions: These data suggest that muscle attenuation and area are independently associated with RTD and peak torque; and that area and attenuation demonstrate similar contributions to RTD.