Scientists have discovered a remarkable method for making your body immune to the metabolic benefits of exercise: It’s called working an office job.

The idea that long bouts of uninterrupted sitting might be bad for your health has gotten lots of attention over the past decade. The reason may seem obvious: If you’re sitting all the time, you’re not exercising. But emerging evidence suggests that there’s a deeper connection between sedentary time and lack of exercise, with the combination of both worse than either one on its own.

In a new study published in the Journal of Applied Physiology, researchers at the University of Texas show that four days of prolonged sitting induces a state that they call “exercise resistance.”

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They had 10 volunteers complete two four-day protocols that involved sitting around for more than 13 hours a day while taking fewer than 4,000 steps. At the end of one of the four-day periods, they did a vigorous one-hour treadmill workout.

Normally a one-hour workout would produce a set of metabolic benefits that persist for at least a day. Your insulin sensitivity and glucose tolerance, both of which are associated with heart health, improve immediately. And your postprandial lipemia – the rise in triglycerides circulating in your blood after a fatty meal, which may contribute to blocked arteries – will be attenuated.

But when the researchers fed their volunteers a high-fat, high-sugar slurry of melted ice cream and half-and-half creamer the next day, their blood sugar, insulin and triglyceride levels shot up by the same amount regardless of whether they’d exercised the night before. After all the sitting, their workout no longer packed its usual health punch.

One of the unanswered questions in the too-much-sitting debate has been whether exercise and sitting are independent risk factors. If you sit all day at work, can you counteract any negative effects by getting lots of exercise?

Instead, the new results add to evidence that the two are linked: Those who sit the most benefit the least from a given amount of exercise.

While the Texas study doesn’t explore how these links occur, previous research in rats has shown that a series of metabolic changes take place when muscles don’t contract for long periods of time. For example, levels of an enzyme called lipoprotein lipase, which helps regulate triglyceride levels, are decreased.

Whether you’d see the same exercise resistance after a single day of sitting isn’t yet clear, says Dr. Edward Coyle, director of the University of Texas’s Human Performance Laboratory and senior author of the study.

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Still, the results argue against chaining yourself to your desk during the work week and then hoping to compensate by getting extra exercise on the weekend. Earlier results from Coyle’s lab suggest that getting 8,000 to 10,000 steps throughout the day is enough to ward off exercise resistance and ensure that you get metabolic benefits from whatever exercise you do.

Of course, it’s almost impossible to make a clear distinction between lack of exercise and too much sitting, points out Dr. Travis Saunders, a University of Prince Edward Island researcher who studies sedentary behaviour. Does getting 10,000 steps over the course of a day count as “exercise,” or merely as breaking up your sitting enough that you can benefit from further exercise?

That’s why the Canadian Society for Exercise Physiology and other groups recently changed their physical activity and sedentary behaviour guidelines for children to 24-Hour Movement Guidelines that integrate recommendations for sitting, sleeping, light activity and more vigorous exercise.

“In a lot of ways, it makes more sense to focus on the combinations of these behaviours, rather than looking at them in isolation,” Saunders says.

That’s probably as good a takeaway as any from the new findings. It’s never about one great workout (or, conversely, about one missed workout); nor is it about one day glued to your chair. It’s about how they all add together. If you can find ways of staying at least minimally active during even the busiest weeks, you’ll ensure that you maximize your benefits when you do make it back to the gym.

Alex Hutchinson is the author of Endure: Mind, Body, and the Curiously Elastic Limits of Human Performance. Follow him on Twitter @sweatscience.

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