The Physical Activity Paradox in Low Muscle Mass in Middle-Aged and Older Adults.

Introduction: Physical activity is widely accepted as a therapeutic approach to age-related muscle mass loss. However, it is unclear whether all physical activity domains benefit muscle mass maintenance. This study investigated the association between low muscle mass and domain-specific physical activity, including leisure-time and occupational moderate-to-vigorous physical activity (MVPA).

Methods: This study included 27,357 middle-aged and older individuals (≥40 years) whose data were collected from 2014 to 2022 and analyzed in 2024. Low muscle mass was defined as a muscle mass index 2 SDs below the sex-specific average of 9,426 young individuals (aged 20-39 years). Leisure-time and occupational MVPA were assessed using the Global Physical Activity Questionnaire and categorized as 0 min/wk, 1-149 min/wk, and ≥150 min/wk. Logistic regression analysis focused on all participants, and additional analyses stratified by sex, age, sedentary time, and transfer time were performed.

Results: For leisure-time MVPA, participants with 1-149 min/wk and ≥150 min/wk had significantly lower odds of low muscle mass compared to those with no MVPA, with ORs of 0.795 (95% CI=0.691, 0.914) and 0.740 (95% CI=0.649, 0.843), respectively (p<0.01 for both). No significant association was found between occupational MVPA and low muscle mass. These findings were consistent across different strata of sex, age, sedentary time, and transfer time.

Conclusions: Leisure-time MVPA is inversely associated with low muscle mass, whereas occupational MVPA shows no association, highlighting the importance of dynamic movements of sufficient intensity and recuperation time in maintaining muscle mass.