The Invisible Burden of Office Work: A Dose-Response Analysis of Working Hours and Upper and Lower Extremity Musculoskeletal Pain in Korea (A Cross-Sectional Analysis of the 7th Korean Working Conditions Survey)

Background The dose-response relationship between working hours and musculoskeletal disorders (MSDs) remains poorly understood, particularly among office workers. This study investigated the association between weekly working hours and the prevalence of upper extremity, lower extremity, and co-existing musculoskeletal pain in Korean office workers. Methods We analyzed 11,368 non-shift office workers from the 7th Korean Working Conditions Survey. Weekly working hours were categorized as: <40, 40 (reference), 41–52, and >52 h. Odds of self-reported musculoskeletal pain were estimated using weighted logistic regression models, adjusting for sociodemographic, occupational, and ergonomic factors (bad posture, repetitive movements, prolonged sitting). Effect modification by sex was tested. Results Compared with the 40-h workweek, working 41–52 h had higher odds of upper extremity (odds ratio [OR] 1.45, 95% confidence interval [CI] 1.24–1.69), lower extremity (OR 1.66, 95% CI 1.34–2.05), and co-existing pain (OR 1.63, 95% CI 1.27–2.09). Working >52 h demonstrated the highest likelihood of pain, with ORs exceeding 3.1 for all outcomes. These dose-response associations remained robust independent of ergonomic hazards and consistent across sexes (P>0.05). Notably, males working <40 h exhibited higher odds of co-existing pain (OR 2.21, 95% CI 1.06–4.60), suggesting a health selection effect. Conclusion Working >40 h per week is associated with a progressively increased likelihood of musculoskeletal pain among Korean office workers, independent of physical workplace hazards. This association is consistent across sexes. Occupational health strategies should target both extreme overwork and moderate overtime (41–52 h).