Muscle Mass Mediates the Effect of Physical Activity and Sedentary Behavior on Metabolic Syndrome, with Differences...

This study examined whether skeletal muscle mass mediates the relationship between sedentary behavior, physical activity, and cardiometabolic health, and if this relationship differs by genders.

Secondary analysis was conducted using data from the 2022-2023 Korean National Health and Nutrition Examination Survey (n = 5956). Cardiometabolic abnormalities were defined as having one or more of the five metabolic syndrome (MS) criteria, while MS was defined as having three or more. Muscle mass relative to body weight was measured by bioelectrical impedance analysis. Sedentary time and recommended moderate-to-vigorous physical activity (MVPA) levels at work, for transportation, and for recreation (≥600 Mets), and strength training (≥2 times/week), were assessed using the Global Physical Activity Questionnaire.

Higher MVPA (p < 0.001) and less sedentary time (p < 0.01) were significantly correlated with greater muscle mass in middle-aged and elderly men and women. Mediation analyses, which controlled for MS risk factors, revealed gender differences. In men, the indirect effects of sedentary time, MVPA, and strength training on both cardiometabolic abnormalities (b = 0.007, CI [0.003, 0.013]; b = -0.066, CI [-0.110, -0.033]; b = -0.074, CI [-0.110, -0.033]) and MS (b = 0.007, CI [0.003, 0.011]; b = -0.060, CI [-0.095, -0.032]; b = -0.065, CI [-0.100, -0.035]) were significant, indicating mediation by muscle mass. In women, the indirect effects of these three behaviors on cardiometabolic abnormalities were also mediated by muscle mass (b = 0.003, CI [0.001, 0.006]; b = -0.014, CI [-0.031, -0.002]; b = -0.023, CI [-0.050, -0.003]). However, for MS, sedentary time (b = 0.057, p < 0.001) and MVPA (b = -0.222, p < 0.05) had only direct effects, with no mediation by muscle mass. Furthermore, strength training showed no significant effects.

These findings suggest that promoting MVPA and strength training, while reducing sedentary time, can improve cardiometabolic health by increasing muscle mass, though the mediating role of muscle mass for MS differs by gender.