Computed tomography-based muscle attenuation and electrical impedance myography as indicators of trunk muscle strength independent of muscle size in older adults.

OBJECTIVE The aim of this study was to examine the associations of computed tomography-based x-ray attenuation and paraspinal electrical impedance myography measures of trunk muscles with absolute and relative (normalized by body weight) trunk extension strength, independent of muscle cross-sectional area. DESIGN This is a cross-sectional study of mobility-limited community-dwelling older adults (34 women, 15 men; mean [SD] age, 78.2 [7.2] yrs) recruited from within an existing prospective research cohort. Trunk extension strength, computed tomography-based trunk muscle cross-sectional area and attenuation at L4 level, and paraspinal electrical impedance myography measures were collected. RESULTS Attenuation was positively correlated with absolute and relative strength for multiple muscle groups (r = 0.32-0.61, P < 0.05). Paraspinal electrical impedance myography phase was positively correlated with paraspinal attenuation (r = 0.30, P = 0.039) and with relative strength (r = 0.30, P = 0.042). In multivariable linear regressions adjusting for sex and cross-sectional area, attenuations of the anterior abdominal muscles (semipartial r = 0.11, P = 0.013) and combined muscles (semipartial r = 0.07, P = 0.046) were associated with relative strength. CONCLUSIONS Although attenuation was associated with relative strength, small effect sizes indicate limited usefulness as clinical measures of muscle strength independent of muscle size. However, there remains a need for additional studies in larger and more diverse groups of subjects.