Exercise Helps the Heart, But Can Manual Labor Hurt?

May 12, 2021 — All exercise is not created equal, and the exercise you get during leisure time is better for your heart health than on-the-job exercise. In fact, on-the-job physical exercise may actually be harmful to heart health, according to a study published in April.

The difference in leisure-time exercise and workplace exercise is a phenomenon sometimes called the “physical activity paradox,” lead study author Andreas Holtermann, PhD, of the National Research Center for the Working Environment in Copenhagen, Denmark, tells WebMD.

“Our findings suggest that clinicians, patients, and managers ought to be aware that having a manual physical activity-demanding job might not improve fitness and health of the workers, while health-enhancing leisure-time physical activity ought to be promoted,” he says.

Do Exercise Guidelines Apply to Everyone?

According to the World Health Organization and the U.S. Department of Health and Human Services, physical activity is essential to maintain and improve health, but these guidelines do not distinguish between leisure- and work-time physical activity. But some research has suggested that physical activity required at work may not provide the same benefits and may even increase heart risk.

These previous studies weren’t robust enough to offer definite conclusions. Also, “much of the existing evidence on physical activity and health is predominantly from leisure-time physical activity among higher-educated white-collar populations,” Holtermann says. The question is whether they apply to on-the-job exercise in other groups.

To home in on the differences between manual labor and leisure-time exercise, Holtermann and his team used data from 104,046 adults (between 20 and 100 years old) who took part in the Copenhagen General Population Study from 2003 to 2014. Participants came from the greater Copenhagen area, which included high- and low-income regions.

Participants self-reported their leisure and occupational physical activity, demographic, lifestyle, medical information, and living conditions. They also had a physical exam that included height, weight, resting blood pressure, and heart rate. Participants were then followed for an average of 10 years.

Quantity vs. Quality

During the follow-up period, there were 9,846 deaths from all causes (9.5% of participants) and 7,913 major heart events, such as fatal or nonfatal heart attacks or strokes (7.6% of participants).

High levels of leisure-time activity were associated with a lower risk of heart events and a lower risk of death. But lots of physical activity at work was linked to more chances of heart attacks and strokes and a higher risk of death.

Holtermann says the findings might seem “surprising,” in light of the recommendation from the World Health Organization that “all steps count toward better health.”

However, he has had “many years of experience” measuring physical activity demands placed upon manual laborers and has “long experience discussing this topic with employees and managers, unions, workplaces, and policymakers.”

To people working in these settings, “it is nothing new that the health effects of physical activity in work differ.” But many do not “consider the guidelines to be for them, but for higher-educated white-collar workers,” he says.

He pointed to other differences between work- and leisure-time exercise.

“I think the main important difference is the massive difference in dose — often 6 to 8 hours of physical activity at work on several consecutive days, compared to 30 to 60 minutes at leisure some days a week,” he says.

Controversial Findings

An accompanying editorial by Martin Halle, MD, and Melanie Heitkamp, PhD, both of the Technical University of Munich in Germany, takes issue with the study findings.

The “evidence from numerous populations and continents has broadly and consistently shown that regular physical activity has beneficial effects on cardiovascular health and premature mortality, a scientific finding that has been widely implemented in guidelines of the WHO [World Health Organization] as well as the European Society of Cardiology,” they write.

The editorial nevertheless suggests some possible explanations for the “physical activity paradox” found in the current study. Leisure-time exercise often may be more aerobic, while occupational exercise may involve “repetitive resistance exercise of short bouts and often insufficient recovery time.”

Also, “workers in heavy manual jobs may be particularly exposed to psychological factors (eg, night shifts and environmental stressors such as noise or air pollution),” they speculate.

Interpret With Caution

Genevieve Dunton, PhD, a professor in the departments of Preventive Medicine and Psychology at the University of Southern California, also had reservations about the study’s implications, saying the results “should be interpreted with caution.”

Although there is “certainly a plausible argument that occupational physical activity provides fewer cardiovascular benefits than leisure-time physical activity … the data may not support going as far as claiming that occupational physical activity on its own is detrimental to cardiovascular health,” she says.

The study omits two factors that could “explain the observed association” and were not accounted for by the researchers, she says: emotional responses during physical activity and overall psychological stress.

“Individuals may experience more positive emotional responses … during leisure-time vs occupational physical activity, which could lead to more mental health benefits and lower risk of cardiovascular events/mortality,” she says.

Also, she says, those who work in manual labor have more psychological stress than those who have the time and resources for leisure-time exercise.

Without taking that emotional stress into account, “we need to be very tentative about claiming that occupational physical activity raises risk of cardiovascular events and death,” Dunton says.

Triple Burden

Commenting on the study for WebMD, Andrew Freeman, MD, co-chair of the American College of Cardiology’s Nutrition and Lifestyle Work Group, says that although physical activity — including exercise at work — is generally helpful, “dedicated physical activity is good for the heart, mind, and body, and that’s probably the most important point that this study captures.”

Workplace exercise is often stressful and also associated with work-related responsibilities. “Exercising for a dedicated period — ‘this is for me’ — and especially being outdoors in nature, where many people walk or jog, is good for cardiovascular health,” he says.

Holtermann agrees, noting that physical activity at work is controlled by the work production, while recreational exercise is tailored to personal needs, motivation, and context, he says.

 “The people having the non-healthy manual work are also those with less resources and possibilities, which is a triple burden that may have a significant role in explaining the socioeconomic gap in health,” he says.