Trunk muscle quality and quantity predict the development of metabolic syndrome and the increase in the number of its components in individuals without metabolic syndrome

Abstract Background and Aims The metabolic syndrome has been reported by cross-sectional studies to have an association with skeletal muscle quality and quantity. Using a longitudinal study design, this study aimed to explicate the association between muscle characteristics assessed with computed tomography (CT) and the incidence and progression of metabolic syndrome. Methods and Results In this retrospective study on a cohort of employees undergoing annual physical examinations, we evaluated data from 554 participants without metabolic syndrome. The cross-sectional skeletal muscle area was determined based on CT data at the level of the third lumbar vertebra, and the skeletal muscle density (SMD) and index (SMI) were measured. The participants were divided into four study groups according to the sex-specific median values for SMI and SMD. We followed the participants for a mean period of 3.1 years. In the sex- and age-adjusted model, SMI and SMD had an interaction effect on the longitudinal change in number of metabolic syndrome components (β=-0.074, p=0.0727). Multiple regression analyses revealed that both low SMI and SMD was significantly associated with the change (β=0.131, p=0.0281), whereas the low SMI and high SMD, and high SMI and low SMD were not. Both low SMI and SMD (hazard ratio, 2.42; 95% confidence interval, 1.28–4.78) showed an increased adjusted hazard ratio for incident metabolic syndrome. Conclusion The participants with both low quality and quantity skeletal muscle were associated with the incidence and progression of metabolic syndrome, whereas those with only low quantity or quality of skeletal muscles were not.