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

Abstract

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 (β) indicate association effect sizes.

Results: In the fully-adjusted models, attenuation (men β = 0.06, 95% CI: 0.01, 0.11; women β = 0.07, 95% CI: 0.03, 0.11) and muscle area (men β = 0.13, 95% CI: 0.07, 0.19; women β = 0.10, 95% CI: 0.06, 0.15) were associated with knee RTD. Attenuation (men β = 0.12, 95% CI: 0.08, 0.16; women β = 0.12, 95% CI: 0.09, 0.16) and muscle area (men β = 0.38, 95% CI: 0.33, 0.43; women β = 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.

Figure 1.

(A) Scan of the left and right thigh. Asterisk indicates water equivalent cell of computed tomography calibration phantom. Manual contour tracings of the sartorius (outlined in green), quadriceps (purple) and hamstrings (red). (B) Soft tissue mappings of processed images; intra-muscular adipose tissue area defined as area of subfascial adipose tissue (light blue) within the quadriceps map, relative to the size of the quadriceps. Please see online version for color maps. Images courtesy of Dr. Thomas Lang, University of California, San Francisco.

Figure 2.

Muscle composition and function by 5-year age groupings and sex. Bars are 95% confidence intervals of median % differences from the reference group (65–69 years). Attenuation is inversely related to myocellular lipid content (10,11). IMAT = Percentage Intra-muscular Adipose Tissue Area; RTD = Rate of Torque Development. Differences across age groups within sex were all p < .001. Wilcoxon Rank Sum tests compared men and women within age group. *p < .01 adjusted for multiple comparisons.