Skeletal Muscle Strength and Waist-to-Height Ratio Serve as Partial Mediators in the Relationship Between Muscle Mass and Exercise Capacity in Individuals with Heart Failure: A Mediation Analysis.

Abstract

Objective: Exercise intolerance is a hallmark of heart failure (HF), and skeletal muscle abnormalities and abdominal obesity are important noncardiac factors contributing to this limitation. This study aimed to investigate the mediating roles of skeletal muscle strength and waist-to-height ratio (WtHR) in the relationship between muscle mass and exercise capacity in individuals with HF.

Method: This cross-sectional study included 110 patients with HF aged over 18 years who were classified as New York Heart Association (NYHA) functional class II or III. Exercise capacity, skeletal muscle mass, muscle strength, and WtHR were assessed using the six-minute walk test, a Tanita device, a Jamar hydraulic handgrip dynamometer, and a tape measure, respectively. Mediation effects were evaluated using the bootstrapping method with a 95% confidence interval and parallel multiple mediation models. Mediation was considered significant when the intervals did not include zero.

Results: A significant correlation was observed between muscle mass and exercise capacity, with both muscle strength and WtHR acting as partial mediators in this relationship. After adjusting for age, sex, and NYHA class, the mediating effect of WtHR was greater (30.6%) than that of muscle strength (17.9%). Despite these mediating effects, muscle mass maintained a direct effect of 51.5% on exercise capacity.

Conclusion: In individuals with HF, muscle mass is associated with exercise capacity both directly and indirectly through muscle strength and WtHR. Assessing these characteristics together may help account for the impact of abdominal obesity, which is associated with reduced exercise capacity in this population.