Regular exercise helps to bulk up our brains and improve thinking skills, numerous studies show. But physically demanding jobs, even if they are being carried out in an office, might have a different and opposite effect, according to a provocative new study of almost 100 older people and their brains and work histories. It finds that men and women who considered their work to be physically draining tended to have smaller memory centers in their brains and lower scores on memory tests than other people whose jobs felt less physically taxing.

The study does not prove that physical demands at work shrunk people’s brains. But it does raise interesting questions about whether being physically active on the job might somehow have different effects on our brains than being active at the gym or out on the trails.

Most of us probably expect that physical activity is physical activity and its benefits and impacts should be about the same, no matter where or under what conditions the activity occurs. But a growing body of science suggests that context matters. In studies with lab rodents, for instance, similar amounts of exercise can lead to contrasting health outcomes, depending on whether the animals run voluntarily on wheels, meaning they control their own workouts, or are placed on little treadmills, with researchers manipulating the pace and duration of their exertions. In general, wheel workouts produce healthier rodents than treadmill training.

Some studies with people have identified a related dynamic. For most of us, under most conditions, being physically active reduces our risk of dying young. But in multiple epidemiological studies, people — and in particular, men — whose jobs require physical labor face heightened risks of premature death, compared to men working in relatively sedentary professions, even when researchers control for factors such as income, body weight, smoking and socioeconomic status. Most researchers suspect that cumulative, added physical and psychological stress from exertions on the job is likely to contribute to this outcome. But the causes remain unknown.

Recently, researchers at Colorado State University in Fort Collins, the University of Illinois at Urbana-Champaign and other institutions began to wonder whether there might be a similar interaction between occupational physical activity and brain health. A wealth of studies show strong relationships between working out and healthier brains and minds, but we know little about whether the physical exertions we might do at work likewise influence the shape and workings of our brains

So, for the new study, which was published in July in Frontiers in Human Neuroscience, the scientists turned to an existing group of volunteers. Aged at least 60, these men and women had participated a few years before in a neuroscience study involving brain scans, medical exams, cognitive work-ups and questionnaires about their exercise habits and lifestyles. All were cognitively healthy for their age.

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Now, the researchers asked these people if they would complete detailed questionnaires about their current or most recent job, and if they were unemployed or retired. The questionnaires asked about their professions and whether they considered their job to be physically demanding, meaning it involved, in their opinion and experience, some amount of labor. The researchers also asked about the jobs’ cognitive demands — did the work involve decision-making, task juggling, planning and so on — and general workplace conditions and stresses, such as workloads and relations with co-workers and bosses.

They got completed questionnaires from 99 of them. The scientists compared their answers now with their brain scans and cognitive test scores from a few years before and found some interesting relationships.

The researchers had expected to see links between cognitively demanding jobs and greater volumes in people’s hippocampus, which is a portion of the brain involved in memory and thinking. But those links did not exist: The researchers found no significant relationships between thinking on the job and better brain structure or cognitive test scores. They also saw no meaningful associations between considering your workplace psychologically stressful and the state of your brain.

But there were associations between physical job demands and the brain. People who reported that their job drained them physically turned out also to be people with relatively smaller hippocampal volume and lower scores on their memory tests, even after the researchers controlled for their socioeconomic status, income and whether they exercised during their off hours. Few of these workers were laborers. Most had office jobs. But their brains looked different if they felt that their jobs were physically hard than if they did not.

Outside of work, though, moving was a plus. Those people who reported regular physical activity on their own time generally had greater hippocampal volume and better memories than inactive people. But physical activity at work did not amplify those benefits; it dampened them.

The implications of these results are murky but worrying, said Aga Burzynska, an assistant professor at Colorado State University who led the new study. It is possible that exercise affects the brain one way and “occupational physical activity has a different” and perhaps less-desirable effect, she said.

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But many questions remain unanswered. People self-reported their job’s physical demands, she points out; the researchers did not measure energy expenditure, so one person’s draining exertions may have involved filing, while someone else was hefting loaded crates. The researchers also did not delve into workers’ sense of agency, so they do not know if feeling coerced into moving affected outcomes, or how occupational activity could have affected brains at all. Fatigue, stress hormones, differing levels of various brain chemicals or other factors might play a role, Burzynska said.

Most important, the study does not show that physically demanding work causes brains to change, she said, only that “they are related in some way.”

The findings do suggest, though, that we need to better understand and consider the complex interplay of work, stress, physical activity — on the job and elsewhere — and the health of our brains, Burzynska said. The relationship between physical demands, our jobs and our brains may be especially relevant now, during the pandemic, when work and home so often overlap.