Why was this study done?
Because most people spend the bulk of their waking hours at work, health promotion researchers want to know the impact of work conditions on people’s levels of physical activity outside work. However, most studies on this topic are cross-sectional in design. That is, they draw on data about work characteristics or physical activity from a single moment in time. Few studies on the topic are set up to follow a group of workers and examine changes over time. This study aimed to do just that.
How was the study done?
The study drew on seven cycles of the Canadian National Population Health Survey (including the 1994 baseline and every two years between 2000 and 2010). The survey collected health and sociodemographic information from a nationally representative sample of Canadian residents of all ages. It asked about levels of physical activity using three categories: inactive (equivalent to walking less than 30 minutes a day), moderately active (walking 30 to 60 minutes a day or doing an hour-long exercise class three times a week), and active (walking an hour or jogging 20 minutes every day). The survey also asked about work factors such as skill discretion (opportunity to learn and use higher skills), decision authority (ability to decide how to do one’s job), psychological demands and physical exertion. The number of jobs, number of hours worked and type of shifts worked were also examined.
This study examined the results over the survey’s three cycles of about 6,400 respondents who worked at least 15 hours a week (but not self-employed).
What did the researchers find?
Among the 6,400 workers, about half did not report changing their leisure-time levels of physical activity over the study’s 12-year period.
For the 3,189 workers who did experience a change in physical activity levels, several work factors were modestly linked with the likelihood of their increased levels of physical activity. Those whose jobs had lower skill discretion, higher psychological demands, higher physical demands and longer hours of work were one to seven per cent less likely to see their levels of physical activity rise during the 12-year period. No difference was found on the basis of age, sex or work factors such as decision authority or type of work shifts.
What are the implications of the study?
The findings seem to support the theory that people who experience physical or psychological fatigue at work may lack the motivation to engage in more physical activity at home. Although the size of the effect is small, the findings support the evidence on the potential role of work factors in influencing physical activity outside of work.
What are some strengths and weaknesses of the study?
A strength of the study was its use of a large population sample and a long follow-up period of more than 12 years. Another strength was the study’s use of a novel analytical approach, called “fixed effects,” which allowed the research team to account for individual characteristics that don’t tend to change over time and that are not captured in the survey questions. (Examples may include individuals’ attitudes about physical activity or individuals’ tendencies to over- or under-report work factors or physical activity levels.) By accounting for these variables, the number of potentially confounding variables was kept to a minimum.
A weakness of the study was its reliance on workers self-reporting their off-hours physical activity, which may not be accurate. Furthermore, findings may reflect the influences of wider socioeconomic factors on work factors and physical activity, influences that were not examined in the study.