Workers doing vigorous, tiring activity all day no healthier than those who are least active

Which of the following workers have a healthier heart? The desk-bound office worker who bikes to work and jogs at night? The health-care worker who constantly shifts gears between light duties and highly physical tasks? Or the construction worker whose job is strenuous from the beginning to end of a shift?

A study by the Institute for Work & Health (IWH) explored these questions using, for the first time, a large and nationally representative sample of Canadian workers and minute-to-minute activity tracker data.

It found Canadian workers’ physical activity habits generally fall into one of six patterns. Not surprisingly, one of the largest groups of workers, making up 31 per cent of the sample of 8,909 participants, are those with low physical activity. These might be, for example, people who commute mostly by car, get up from their desks just to go to the water cooler, and do only light activity such as short walks and household chores in their off-hours.

Compared to this group—let’s call them the sedentaries as a shorthand—almost all other groups have better heart health down the road. Whether they’re fitness buffs or only on the move mainly for work, almost all workers who do various levels of moderate or intense physical activity throughout the week have lower risks of cardiovascular diseases 10 years later.

Almost all. The study team found one group of Canadian workers who have no better heart-health outcomes despite engaging in vigorous levels of physical activity for much of the work day.

This group, making up just eight per cent of the overall study sample, are likely workers who are in physically demanding jobs, such as construction work. Their risk of developing heart disease over 10 years is not statistically different from that of the sedentaries.

The implication of this finding is that workers getting their physical activity outside of work might be benefiting their heart more than those solely getting their physical activity doing work, says Dr. Avi Biswas, IWH associate scientist and lead author of a paper on the study, published in May 2022 in the Journal of the American Heart Association (doi:10.1161/JAHA.121.025148).

This study adds to a growing body of research on what’s called the physical activity paradox, says Biswas, who presented the study at an IWH Speaker Series webinar (link) in June 2022. Physically demanding work with very little rest is not giving workers the benefits that they might think are associated with physical activity, he adds. If you're doing high levels of physical activity at work and putting your body through a lot of strain, that's not health promoting.

Drawing on activity tracker data

In this study, Biswas and team set out to first understand how Canadians actually move, rather than relying on what people report in surveys about how much they move (which can be more inaccurate). The team drew on an existing, nationally representative dataset from Statistics Canada’s Canadian Health Measures Survey (CHMS). In this survey, conducted over five cycles between 2007 and 2017, participants were asked to wear an accelerometer on their right hip during waking hours for seven consecutive days.

Survey participants also agreed to have their clinical data collected, including data from blood and urine samples submitted at testing centres. With this clinical data, the team calculated participants’ risk of cardiovascular disease over 10 years, using a well-tested formula developed by the American College of Cardiology/American Heart Association Task Force on Practical Guidelines. Finally, participants were also asked to complete a household survey covering a range of questions on lifestyle and health behaviours.

The team focused only on CHMS participants aged 18 to 65 who were working—and who had neither a pre-existing heart disease nor a health condition that would prevent them from physical activity. Using accelerometer data, the team sorted the sample of 8,909 participants into clusters of people who had similar activity patterns throughout the day. They found six patterns, in varying group sizes.

Six profiles

The six groups of workers, characterized by similar physical activity patterns, are:

1. The sedentaries (2,898 workers)—This group engages in low or light activity all through the day, both during at-work and off-work hours. Some office workers might be among this group. (Note, though, that the study did not specifically ask about respondents’ occupations, so job examples are only conjecture). Workers in this group are the least likely to use active modes of transportation. They also report low levels of recreational physical activity.
2. The steady movers (3,219 workers)—This group has moderate activity levels throughout the day, followed by light activity during the evening hours. They may include workers who are constantly on their feet at work, such as sales associates. They report low levels of physical activity for recreation. Compared to the sedentaries, they have a 14 per cent lower risk of heart disease over 10 years.
3. The dynamic movers (1,194 workers)—This group alternates between light activity and moderate activity throughout the day. They are the second most active group when it comes to recreational activities, though they report low levels of active transportation. This group may include early childhood educators or health-care workers whose work day can be a mix of low activity and bursts of physical movement. Compared to the sedentaries, this group has a 27 per cent lower risk of heart disease over 10 years.
4. The physical workers (713 workers)—This group engages in vigorous physical activity—activity that makes one sweat and breathe hard—and sustains it throughout most of their daytime hours. Construction workers may be among this group. This group’s risk of heart disease does not differ from from that of the sedentaries in a statistically significant way.
5. The night shifters (225 workers)—This group stays moderately active from midday through to midnight. Grocery clerks stocking shelves into the late evening may be among this group. With an average age of 34, workers in this group are the youngest of the six; they are also the ones most active in their commutes.  This group’s risk of heart disease is 33 per cent lower than that of the sedentaries.
6. The exercisers (750 workers)—This group spends parts of the work day doing light or moderate activity, but also engages in vigorous physical activity at the start of the day, around noon, and again in the late afternoon and early evening. Members of this group may include office executives with high flexibility and job control. This group has the highest level of recreational physical activity (in both time spent and prevalence). It also has the largest percentage of participants using physically active modes of transportation. Of the six groups, these exercisers have the highest income and tie for the highest level of education. This group has 42 per cent lower risk of heart disease compared to the sedentaries.

Limitations of the study

Biswas cautions that the survey did not directly ask participants about when they were at work, so the activity patterns described above were inferred from the time-of-day information (about 80 per cent of study participants said they had a standard nine-to-five work schedule). He notes, as well, a second limitation associated with the kind of movement captured by accelerometer devices.

Even if they give more precise estimates of physical activity over a continuous day and week, because accelerometer devices are worn on the hip, they may not capture things that people do with their arms, or when they bend down to lift, push and pull—things that are associated with physically demanding jobs. As a result, we're not likely to capture that information very well, says Biswas.

Although the CHMS survey sample was designed to reflect the demographic makeup of the Canadian population at large, the sample is likely skewed towards participants who have the resources and flexibility to take part in such an onerous study (one involving daily visits to a testing centre over a week). As a result, participants may be more motivated by health and fitness than average Canadians.

Besides the implication of the study findings for people in physically demanding work—i.e. the lack of heart-health benefits from manual labour—Biswas also highlights a potential positive for people who move moderately throughout the day. It can be very hard for many people to meet the physical activity guidelines [of 150 to 300 minutes of moderate intensity a week], he says. Based on what we actually saw in our sample, it seems that there’s a sizable proportion of people doing moderate levels of activity—and getting heart-health benefits.

Biswas encourages people who find physical activity guidelines daunting to think of ways they can do moderate activity throughout the day. To me, that’s the key takeaway from this study. Moderate activity doesn’t always have to be exercise. It can be taking brisk walks, mowing the lawn or cleaning windows—things that people have to do anyway. If people think about the health benefit of doing more moderate activity in a day, this might be a more feasible target to focus on, he says.