A research paper published in the British Journal of Sports Medicine took data from 17 previous studies and found what the authors are calling a “physical activity paradox”.

So, while exercise in leisure time is proven to be good for you, the exercise you get as part of a physically demanding job may not be.

This study found men in physically demanding jobs were at an 18 per cent increased risk of early death, compared to men in work with low levels of physical activity.

What’s more, the researchers only found this link between strenuous work and early death in men, not women.

Is the risk in active jobs or other social factors?

Some of the earliest studies demonstrating the health benefits of physical activity were actually based on people who were active as part of their jobs.

Landmark research in the 1950s looked at the difference between London Transport Authority conductors, whose jobs kept them active, and drivers, whose jobs kept them relatively sedentary. The drivers were found to be at higher risk of coronary heart disease.

But there’s a big difference between the kind of physical activity a transport conductor does, and other types of manual labour — for example road work, and construction jobs.

Since the 1950s, many physically strenuous jobs have been made superfluous by technological advances, suggested Professor Jo Salmon from Deakin University’s Institute for Physical Activity and Nutrition, who was not involved in the study.

“Times have changed and we know there’s not that many highly active occupations left,” she said.

Professor Salmon also pointed out that physically strenuous jobs today are often held by people from lower socioeconomic backgrounds.

And there’s a lot of research pointing to the fact that people from poorer backgrounds have poorer health outcomes generally.

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“While some of the studies adjusted for things that we call confounders — like smoking, alcohol intake, dietary intake, which are all independent risk factors for premature death — we do know that people who are living in disadvantage are more likely to have these clustered risk behaviours. This is all bundled up together,” Professor Salmon said.

Curtin University’s Professor Leon Straker, who co-authored the paper, agreed socioeconomic status was difficult to extricate from the physical nature of the jobs in the study, and added that these jobs often had additional risk factors, such as chemical exposure or increased sun exposure.

But he thinks the link is still there.

Some of the studies that were analysed as part of the research published on Tuesday tried to control for socioeconomic status.

However, Professor Straker said there was still evidence for physical activity playing a role in risk of death.

Professor Straker said the study showed health guidelines needed to differentiate between the exercise people do as part of their work and what they do in their leisure time.

“Our hypothesis is that the physical activity that people do in work is different to the physical activity people do in leisure, and it’s different in ways that’s really important for how a body responds and becomes fitter, stronger and healthier,” he said.

“If you think about a lot of physically active jobs, they’re often active for really long periods of time, eight hours as a typical workday or longer, and the intensity that they’re working at isn’t necessarily as high as somebody who is going out for a 30-minute run.

“So the intensity’s lower, but it’s over a much longer period of time and you don’t have the same recovery options at work as you do in leisure.”

Professor Straker speculated it could be something about the difference in intensity or the repetitive movements of occupational exercise that might mean men don’t get the same health benefits as they do from leisure activity.