Skeletal Muscle Ratio: A Complete Mediator of Physical Activity and HbA1C in Type 2 Diabetes

Background: An increase in the physical activity level reduces body weight, decreases body fat, increases skeletal muscle mass, and improves serum glucose; however, the influence of body composition parameters on the relationship between physical activity and serum glucose remains unclear. Objective: This study investigated whether skeletal muscle and visceral fat affect the relationship between high physical activity and long-term serum glucose goals. Method: This cross-sectional study recruited patients with type 2 diabetes. The Chinese version of the International Physical Activity Questionnaire was used for estimating the physical activity level, and a bioimpedance device was used to measure the skeletal muscle ratio (skeletal muscle mass/total body weight, %) and visceral fat area (cm²). Hierarchical logistic regression models and mediation tests were conducted according to Hayes’ procedures. Results: Of the total 543 Chinese individuals with type 2 diabetes enrolled, HbA1C levels of fewer than half (n = 243, 44.8%) met the target of ≤7.0%. The skeletal muscle ratio was found to be a complete mediator (OR = 0.920, 95% CI: 0.848 to 0.998; indirect effect: −0.238, 95% CI: −0.525 to −0.020) of the relationship between high physical activity and the target HbA1C level after controlling for visceral fat area (indirect effect: −0.013, 95% CI: −0.183 to 0.156), age, time since diabetes diagnosis, and rice intake. Conclusion: Nurses should include an increase in the skeletal muscle ratio as an objective in physical activity interventions for patients with type 2 diabetes to help them achieve their long-term serum glucose goals.