Moderating Effects of Muscle Fitness on the Associations Between Work Stress, Burnout, and Well-Being Among White-Collar Workers

Background/Objectives: White-collar workers experience a unique dual burden of high psychological demands and prolonged static loading, creating a need to understand how physical resilience may mitigate these stressors. This study investigated the moderating role of specific muscle fitness components in the associations between work stress, burnout, and well-being among white-collar workers. To address the gap in task-specific physical resilience, we employed a cross-sectional design involving 321 full-time employees. Methods: Work stress (job control and demands), burnout, and well-being were assessed via structured questionnaires, while grip strength, abdominal endurance, and back muscle endurance were objectively measured. Results: Results indicated that the muscle fitness components were not directly associated with either burnout or well-being. However, the moderation model for burnout was significant (F = 15.837, p < 0.001; adjusted R2 = 0.278), where back muscle endurance significantly moderated the association between psychological job demands and burnout (β = −0.121, p < 0.05), whereas no such moderating effect was observed for well-being. In contrast, no such moderating effect was observed for well-being, nor did grip strength or abdominal endurance exhibit significant buffering effects on either psychological outcome. Conclusions: These findings demonstrate the relevance of task-specific physical resources in sedentary environments, specifically that back endurance functions as a buffer against burnout but may be insufficient to directly enhance overall well-being. The results suggest that while integrating task-specific physical assessments is vital for burnout prevention, psychosocial organizational support remains essential for fostering comprehensive well-being.