Revisiting the physical activity paradox: the role of cardiorespiratory fitness in workers with high aerobic demands

In contrast to leisure time physical activity, occupational physical activity may have adverse health effects-a phenomenon known as the "Physical activity paradox". Characteristics such as long duration, low intensity, static and restricted movement, body position and insufficient recovery are possible explanations as to why physical activity in the occupational context may "wear one out" rather than provide health benefits. We emphasise the role of low cardiorespiratory fitness as a potential contributor to the physical activity paradox, and present data suggesting that only 25% to 50% of Swedish workers in occupations with higher aerobic demands may have "sufficient" cardiorespiratory fitness to maintain good health during their employment. More research is needed to fully understand the complexity of the role of other confounding factors when examining the relationship between cardiorespiratory fitness and occupational workload. However, we believe that there is an increasing need for general awareness amongst Swedish authorities, employees and employers of the potential health consequences of low levels of cardiorespiratory fitness, especially among workers with high occupational workloads. Importantly, when developing interventions targeting the working situation and/or cardiorespiratory fitness levels among workers, researchers should actively involve the relevant population in the design of the study in order to maximize the effect of the interventions on health outcomes.