Association of Skeletal Muscle Mass with Habitual Exercise, Mealtime and Sleep in Middle-Aged Men: Cross-Sectional Study.

Objective: To investigate the cross-sectional association between skeletal muscle mass and lifestyles including exercise, mealtime, and sleep habits in adult men aged under 64. Materials and Methods: A total of 101 Japanese men aged under 64 who underwent "Anti-aging Health Checkups" were enrolled in the study. Cross-sectional analyses were conducted using the subjects' data such as body mass index, skeletal muscle mass index (SMI), and self-reported lifestyle information. The physical activity (PA) value of habitual exercise per week (metabolic equivalent hr/week) was categorized into three groups. Mealtime combination of breakfast and dinner time was categorized into five groups. A multiple regression analysis demonstrated how each PA group has an association with SMI. Moreover, an analysis of covariance was performed to investigate the association between "mealtime combined with PA" and SMI levels by comparison and to investigate the association between "sleep duration or satisfaction combined with PA" and SMI levels, respectively. Results: The subjects with "breakfast before 8 a.m." had a significant positive association between SMI and PA levels; in addition, among the subjects from the "dinner before 8 p.m." group, as the PA level was higher, the SMI level increased. Consequently, the SMI level increased as the PA level was higher among the subjects who had "breakfast before 8 a.m. and dinner before 8 p.m." Furthermore, sufficient sleep such as more than 6 hr and satisfied sleep had positive associations with SMI as PA levels increased. Conclusion: These findings suggest a potential benefit of habitual exercise with breakfast before 8 a.m., dinner before 8 p.m., and sufficient sleep for maintaining skeletal muscle mass among middle-aged men.