Physical activity is a beneficial and important component of a healthy lifestyle.1–3 Positive associations between physical activity and cardiovascular and all-cause mortality include both leisure time and occupational physical activity.3,4 In the current environment of increasing chronic disease and increasingly sedentary lifestyles, physical activity is strongly advocated to improve and maintain health, and prevent disease. However, not all physical activity is created equal.

In recent years, extreme high volume leisure physical activity, and high volume occupational physical activity have been linked to increased cardiovascular risks.4–11 Extreme bouts of leisure exercise have been linked to changes in cardiovascular measures indicating, perhaps transitory, increases in cardiovascular risks.5–7 These cardiovascular risks associated with extreme leisure exercise are greater among those with greater cardiovascular risks at rest, suggesting extreme leisure exercise among less fit individuals may present greater risks than more fit individuals.5 More concerning, high levels of occupational physical activity have been recognized as having negative impacts on cardiovascular health.4,8–11 Studies of high occupational physical activity workers have recently identified increased cardiovascular and all-cause mortality risks among some of the workers.4,9,10 These paradoxical experiences bring forth questions and uncertainty regarding occupational physical activity benefits.

Current evidence evaluating occupational physical activity has identified older workers as experiencing increased cardiovascular risks with occupational physical activity.4,11 Several investigations have also identified interactions between leisure and occupational physical activity, where individuals who engage in limited leisure time physical activity, and thus are less fit, and have high occupational physical activity jobs may experience increased cardiovascular risks and cardiovascular and all-cause mortality.8–11 This experience of low fitness and high workloads has been linked to increased cardiovascular risks.11,12 Individuals with occupations requiring workloads at higher relative intensity physical activity appear to have the greatest risks with high occupational physical activity.

Past studies of high occupational physical activity risks have identified a mediating effect of leisure exercise on the risks of high occupational physical activity.9,10 Vigorous physical activity during leisure time can reduce cardiovascular risks brought on by high occupational physical activity.10 This finding suggests increasing leisure time physical activity through exercise interventions may reduce the cardiovascular risks associated with high occupational physical activity. Thus, if individuals can improve their overall fitness such that the occupational activity requires a lower relative intensity (i.e., a lower %VO2max), the cardiovascular risks of occupational physical activity may be reduced.

In the present issue of this journal, Korshøj et al.12 present the results of an exercise intervention program among cleaners, a high occupational physical activity job. This randomized controlled trial of moderate exercise training for high occupational workers identified increased ambulatory blood pressure among those randomized to the exercise group. Contrary to previous suggestions, exercise training, aimed to improve physical fitness, further increased the cardiovascular risks experienced by high occupational physical activity workers, as measured with ambulatory blood pressure. More alarming, these increases in blood pressure are more greatly experienced by individuals with the most physically active jobs, or those with jobs requiring the highest relative workloads. Conversely, exercise training led to increases in ambulatory blood pressure only during leisure physical activity for those who engage in less physically active occupations. The authors offer support to the hypothesis that high occupational physical activity combined with leisure exercise training may overload the cardiovascular system and lead to increased cardiovascular risks.11,12

Proposals of cardiovascular risks associated with high volumes of exercise have been suggested through various exercise modalities. A U-curve between exercise volumes and health has long since been proposed, dating back to Hippocrates.13,14 Long-distance aerobic exercise has been associated with increased cardiovascular risks among recreational and elite ultraendurance athletes.5–7,13 Similarly high-intensity exercise sessions beyond 1–2 hours cause cardiovascular damage.15 These recent findings of cardiovascular risks with high occupational physical activity fit within this U-curve theory. The experience of greatest ambulatory blood pressure increase among those with the highest occupational physical activity workloads with exercise training supports these individuals as being beyond the “sweet spot” of moderate exercise volumes.12

In today’s society of increasing sedentary behavior and obesity, occupational physical activity is also declining.16 Consequently, physical fitness may also be declining.17,18 These circumstances create increasing opportunities for unfit workers in high occupational physical activity jobs to experience elevated cardiovascular risks. As Korshøj et al.12 identify, there is a need to develop strategies and interventions to reduce the mismatch of worker occupational demands, and workers’ physical fitness levels. By reducing aerobic workloads required in high occupational physical activity jobs, such workers may be able to continue in their employment without overburdening the cardiovascular system.

Over the past 50 years, occupational physical activity has steadily declined in the developed world.16 Simultaneously, the general population has become increasingly sedentary and chronic conditions are experienced in much higher rates than decades past.1,13,19 Given these lifestyle changes, promoting physical activity among the general population is still encouraged. Among the general population, individuals with the most sedentary jobs report the highest levels of leisure time physical activity.20 Promoting and engaging in physical activity requires a full encompassing approach, considering both leisure time and occupational demands. Individuals engaging in high levels of either leisure or occupational activity should be monitored for increased cardiovascular risks of high physical activity levels.

DISCLOSURE

The author declared no conflict of interest.

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Author notes

Correspondence: Heather Foulds (heather.foulds@usask.ca).