Muscle Density, but Not Size, Correlates Well With Muscle Strength and Physical Performance.

ABSTRACT

OBJECTIVES: There is increasing evidence that muscle volume and mass are poor predictors of muscle strength and physical performance. Other assessments of muscle quality such as skeletal muscle density measured by computed tomography (CT) may be more important. The aim of this study was to explore associations of muscle size and density with handgrip strength (HGS) and the Timed Up and Go test (TUG). We also hypothesized that the strength of these associations would depend on the specific muscle of muscle group, namely trunk, hip, and mid-thigh muscles. DESIGN: Cross-sectional study. SETTING AND PARTICIPANTS: University hospital; 316 volunteers aged 59 to 85 years. METHODS: HGS, TUG, and quantitative CT imaging of the lumber, hip, and mid-thigh were performed in volunteers. From the CT images, cross-sectional area and attenuation were determined for the gluteus muscle, trunk muscle at vertebrae L2 level, and mid-thigh muscle. RESULTS: In men and women, associations of muscle area with TUG were insignificant after adjustment for age, height, and weight. Associations with HGS were only significant in men for the gluteus maximus and the mid-thigh but slopes were rather low (ß < 0.20). Associations between muscle density and TUG/HGS were more pronounced, in particular for HGS. After adjustment, associations with TUG were significant in women for the gluteus maximus and trunk muscle even (ß -0.06, P .001 and ß -0.07, P .031, respectively). CONCLUSIONS AND IMPLICATIONS Muscle density is more strongly associated with muscle strength than muscle size andin women muscle density was also more strongly associated than muscle size with physical performance. Therefore, muscle density may represent a more clinically meaningful surrogate of muscle performance than muscle size. Muscle density measurements of trunk and gluteus muscles can be easily obtained from routine CT scan and, therefore, may become an important measurement to diagnose and screen for sarcopenia.