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

Objective: Exercise intolerance is hallmark of heart failure (HF), and skeletal muscle abnormalities and abdominal obesity are important noncardiac factors contributing to exercise intolerance. 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 HF population.
Method: The cross-sectional study was conducted with 110 HF cases older than 18 years, classified as New York Heart Association (NYHA) functional class II and III. Assessments of exercise capacity, skeletal muscle mass, muscle strength, and WtHR were performed using the six-minute walk test, a Tanita device, a Jamar hydraulic handgrip dynamometer, and a tape measure, respectively. The mediation effects were assessed utilizing the bootstrapping method with a 95% confidence interval and parallel multiple mediation models, which was deemed significant when the intervals did not encompass 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 status, the mediating effect of WtHR was found to be greater (30.6%) than that of muscle strength (17.9%). Despite these mediating effects, muscle mass had 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 via muscle strength and WtHR. Assessing these characteristics together provides the consideration of abdominal obesity, which is associated with reduced exercise capacity in this population.

Keywords: Abdominal obesity, heart failure, muscle strength, Six-Minute Walk Test, waist to height ratio