Comparison of muscle mass and quality between metabolically healthy and unhealthy phenotypes.

Objective The aim of this study was to examine whether higher skeletal muscle mass is associated with a metabolically healthy phenotype and whether muscle quality affects metabolic health. Methods This cross-sectional analysis included 20,659 participants (7,966 women) who underwent abdominal computed tomography scans during health checkups. The total abdominal muscle area (TAMA) on the third lumbar vertebral level was demarcated. Intermuscular adipose tissue and skeletal muscle area were measured. The skeletal muscle area was divided into normal attenuation muscle area (NAMA) and low attenuation muscle area (LAMA). The NAMA/TAMA index was calculated. The metabolically unhealthy phenotype was defined as having two or more components of metabolic syndrome or the presence of hypertension or diabetes. Results TAMA and skeletal muscle area were not significantly different or even lower in metabolically healthy phenotypes compared with metabolically unhealthy phenotypes. However, metabolically healthy phenotypes had significantly higher NAMA (except in women with obesity) and NAMA/TAMA index than in the metabolically unhealthy phenotypes. In people without obesity, lower NAMA/TAMA index was independently associated with higher risk of the metabolically unhealthy phenotype in the fully adjusted model. Conclusions The metabolically healthy phenotypes had more good-quality muscles than did the metabolically unhealthy phenotypes. These results suggest that not only muscle mass but also muscle quality (i.e., degree of myosteatosis) are associated with metabolic health.