Exercise is only beneficial when done outside your job, study claims

New research has revealed a ‘physical activity paradox’

Olivia Petter
Tuesday 15 May 2018 10:03 BST
(Getty Images/iStockphoto)

It’s no secret that exercise can offer endless mental and physical benefits, however, unless you're doing it outside of work hours, high levels of physical activity could be doing you more harm than good, a new study has claimed.

Researchers in the Netherlands claim that a “physical activity paradox” means exercise may only be good for you if it isn’t a part of your job and is conducted in leisure-time.

Manual labour roles such as construction workers are often required to be physically active all day long, however, this means they have an increased risk of dying early, the research states.

“While we know leisure-time physical activity is good for you, we found that occupational physical activity has an 18 per cent increased risk of early mortality for men,” said Pieter Coenen, public health researcher at VU University medical centre in Amsterdam.

“These men are dying earlier than those who are not physically active in their occupation.”

No such correlation was observed for women, in fact, the opposite was true.

According to Coenen, the “physical activity paradox” is due to the difference in the type of exercise that people typically conduct in their own time compared to that which is part of a physically demanding career.

Plus, when exercising during leisure time you’re at liberty to take rest periods when you feel like it.

However, such a luxury may not always be available to you at work, which can exacerbate the negative effects, he added.

Coenen uses the example of going on a 30-minute run outside of work hours.

“That increases your heart rate and you feel well afterwards, but when you are physically active at work, it’s a very different type of activity,” he said.

“You are working for eight hours a day and have limited rest periods. You are lifting, doing repetitive movements, and manual handling.”

He explained that this continuous activity may actually inhibit the functioning of one’s cardiovascular system rather than boost it, as traditional exercise is thought to do.

To gather their findings for the study, which was published in the British Journal of Sports Medicine, the researchers combined results from 17 studies dated from 1960 to 2010, collating data on almost 200,000 people in total.

In addition to levels of physical activity, they examined other lifestyle factors included in the various studies, such as alcohol and smoking.

"The results of this review indicate detrimental health consequences associated with high level occupational physical activity in men, even when adjusting for relevant factors (such as leisure time physical activity),” the researchers concluded.

"This evidence indicates that physical activity guidelines should differentiate between occupational and leisure time physical activity."

However, experts have been quick to point out that the study is limited in its consideration of socioeconomic factors.

“Sedentary work compared to work that requires heavy physical activity is hugely confounded by education, social class and all the other associated behaviours,” said Professor Kay-Tee Khaw, professor of clinical gerontology at the University of Cambridge.

While some of these factors would've been included in studies within the author’s systematic review, they wouldn't all have been factored into every one, despite possibly strongly influencing the risk of early death, he added.

“It is quite possible that very heavy labour may be associated with adverse health. It may also be that these occupations lead to higher accident rates and early mortality without the physical activity itself being the relevant factor which the authors do discuss and I am sure that we need to understand this better.”

He also pointed out that the study focuses on comparing careers involving high levels of physical activity with those that include very low levels and not acknowledging the categories in between.

“This is relevant because most occupations that may involve some physical activity (plumbers, electricians, bus conductors, hairdressers) are much more prevalent that those that involve heavy physical activity such as dock yard workers, builders etc., and so the results do not address these occupations which have moderate physical activity,” he explained.

“Additionally, the sex difference, in particular, the lack of increased mortality in women may well reflect, as the authors discuss, that women do not generally have occupations that require very heavy physical activity and/or the confounding is less marked.”

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