Disentangling longitudinal relations between physical activity, work-related fatigue, and task demands.

Purpose: This longitudinal study examined 'normal', 'reversed', and 'reciprocal' relationships between (1) physical activity and work-related fatigue; and (2) physical activity and task demands. Furthermore, the effects of across-time change in meaningful physical activity groups on levels of employees' work-related fatigue and task demands were studied. These groups were based on employees' compliance with the international physical activity norm.

Methods: Two waves with a one-year time lag of a national representative survey on the quality of work, health, and well-being among Dutch employees were used (N = 2275). Longitudinal effects were tested using Structural Equation Modelling. Meaningful physical activity groups were compared using group-by-time analysis of covariance.

Results: Support was found for reciprocal relations between physical activity and work-related fatigue. It was found that an increase in physical activity is associated with a decrease in work-related fatigue over time and that an increase in work-related fatigue is associated with a decrease in physical activity over time. No significant longitudinal relations were found between physical activity and task demands. Employees whose compliance with the physical activity norm changed over time showed fairly stable levels of work-related fatigue and task demands.

Conclusions: The current findings provide evidence for the potential role of physical activity in the prevention and reduction in work-related fatigue. However, results also indicate that fatigued workers, who would benefit most from physical activity, are less physically active. Our results further indicate that relying on changes in compliance to the physical activity norm may not be the most suitable way to examine changes in work-related fatigue.