Does high occupational physical activity hamper the beneficial health effects of leisure time physical activity? Evidence of the physical activity health paradox from a prospective study on compositional accelerometry data and long-term sickness absence

Background: The ‘physical activity health paradox’ advocates that leisure physical activity (PA) promotes health while occupational PA impairs health. However, this paradox can be explained by methodological limitations of the previous studies—self-reported PA measures, socioeconomic confounding or not addressing the compositional nature of PA. Therefore, this study investigated the association between compositions of accelerometer-based moderate to vigorous PA (MVPA) time at work and leisure and onset of long-term sickness absence (LTSA). Methods: Time spent on MVPA and remaining physical behaviours (sedentary behaviour, standing, light PA and time in bed) at work and leisure was measured for 929 workers using thigh accelerometry and expressed as isometric log-ratios (ilrs). LTSA was register-based events of ≥6 consecutive weeks during 4-year follow-up. The association between ilrs and LTSA was analysed using a Cox proportional hazards model adjusted for remaining physical behaviours and potential confounders, then separately adjusting for and stratifying on education and type of work. Results: During the follow-up, 21% workers experienced LTSA. During leisure, more relative MVPA time was negatively associated with LTSA (20% lower risk with 20 minutes higher MVPA, P=0.02). At work, more relative MVPA time was positively associated with LTSA (15% higher risk with 20 minutes higher MVPA, P=0.02). Beneficial association between MVPA at leisure and LTSA was only observed for the lowest tertile of MVPA at work (P=0.03). Results remained unchanged when adjusted for or stratified on education and type of work. Conclusion: These findings provide further support to the ‘PA health paradox’. Key words: physical activity, sedentary behavior, accelerometers, sick leave, occupational health, time-use epidemiology, register-based sickness absence