The physical activity paradox revisited

Background: The ‘physical activity paradox’ advocates that leisure physical activity promotes health while high occupational physical activity impairs health. However, this paradox can be explained by methodological limitations of the previous studies—self-reported physical activity measures, insufficient adjustment for socioeconomic confounding or not addressing the compositional nature of physical activity. Therefore, this study investigated if we still observe the physical activity paradox in relation to long-term sick absence after adjusting for the abovementioned limitations.

Methods: Time spent on moderate-to-vigorous physical activity and remaining physical behaviors (sedentary behavior, standing, light physical activity and time in bed) at work and in leisure was measured for 929 workers using thigh accelerometry and expressed as isometric log-ratios. Long-term sick absence was register-based first event of ≥6 consecutive weeks of sickness absence during 4-year follow-up. The association between isometric log-ratios and long-term sick absence was analyzed using a Cox proportional hazards model adjusted for remaining physical behaviors and potential confounders, then separately adjusting for and stratifying by education and type of work.

Results: During the follow-up, 21% of the workers experienced long-term sick absence. In leisure, more relative moderate-to-vigorous physical activity time was negatively associated with long-term sick absence (20% lower risk with 20 min more moderate-to-vigorous physical activity, p = 0.02). At work, more relative moderate-to-vigorous physical activity time was positively associated with long-term sick absence (15% higher risk with 20 min more moderate-to-vigorous physical activity, p = 0.02). Results remained unchanged when further adjusted for or stratified by education and type of work.

Conclusion: These findings provide further support to the ‘PA paradox’.