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The Physical Activity Paradox
Why aren't postal workers the healthiest people on earth? After all, the average mail carrier walks more than 10,000 steps a day, which is well above the amounts that we coax people to do for the known health benefits of walking more.
But that is not the case. A growing number of studies show that, even after adjusting for demographics, income, wealth, and family history, people who are active at work are not healthier than their counterparts who exercise in their leisure time. Steelworkers, for example, are less healthy than gym bros, even if they lift the same amount and with the same frequency. Steps as a restaurant server or nurse do not have the same effect as steps around a park at lunch.
The implications are manifold and troubling. For example, a 2021 European Heart Journal study showed that increased work-related physical activity is associated with a higher rate of cardiac events than baseline. A recent The Lancet report showed that high levels of occupational physical activity, far from being protective, are associated with a sharply higher incidence of dementia.
It turns out that where and when you exercise matters at least as much as what you do. This has sometimes been called the "physical activity paradox": while physical activity is generally beneficial for health and well-being when it is part of one's job, it often does not provide the same health benefits—and can even be outright bad in many cases. This paradox has significant implications for public health, occupational health and safety, and our understanding of physical activity's role in overall health.
Why A Step is Not Just a Step
Across almost every kind of exercise, similar activities—stepping, lifting, and so on—are mostly good for you when done outside of work, and mostly less good (and even bad) for you when done inside of work.
It can seem, honestly, baffling. Why does your body care where and why you step, or whether you are a driver lifting UPS packages or a gym bro lifting a barbell? Why does where you do a thing matter, if it's all just exercise? Isn't a step just a step?
A step is not just a step, it turns out. As the following figure from that 2021 paper in the European Heart Journal on the health consequences of the physical activity paradox shows, work- and leisure-related steps are very different in terms of their health effects. In the figure, MACE is short for "major adverse cardiovascular events", and physical activity at work is associated with more MACE: AMI, acute coronary syndrome or ischemic heart disease, stroke, and so on.
