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Comment by goodside | Hacker News Reader

Keep in mind that physical exercise and mental concentration both deplete a common resource pool of glucose in the brain. There are robust, well replicated experiments that show it's significantly harder to perform any mental task while exercising. Daniel Kahneman has a great everyday demonstration of this: While walking with a friend, ask her to multiply two two-digit numbers and see if she slows down. (You can also try it on yourself while jogging at the upper limit of your ability -- it's very noticeable.) Check out the experiments of Roy F. Baumeister for more info.

This isn't to say walking desks are necessarily a bad idea. It's possible that, at low walking speeds, the health benefits of exercise outweigh the impairment of your concentration.

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I have to wonder if training and repetition might make a difference there; for instance, after a week of doing computations while walking, can your friend now multiply faster? The mind is an efficient adapter. It would also be interesting to discover what qualifies as exercise in those studies, and if the benefits of increased circulation and possibly a clearer airway based on improved posture, which presumably also increase brain function, could offset the glucose depletion.

I'm curious if there has been any research into walking slowly on a treadmill, though. The upper level of your ability to job is far more demanding physically. And it's also a bit demanding mentally as your body is busy mapping a route, looking out for stones or cracks you might trip on, etc. Walking slowly on a treadmill with your desk in front of you could yield a very different result.

yes, but walking slowly is nearly indistinguishable from sitting in terms of calorie burn rate.

But maybe it's better in terms of posture for your body, over all? You may burn the same number of calories, but you're up straight, and your joints and muscles are doing something. I'm sure that must be beneficial on its own

Of course

Not the glicose thing really, walking uses very little energy, it would take a lot of exercise to deplete glicose, not walking slowly

but the fact that you can't concentrate while exercise is a huge deal breaker.

Not to mention the fact that while you are walking your head keeps bobbing up and down making it harder to read things.

It's not how much energy is burned in your muscles, it's how much energy is burned in your brain. Walking at any speed requires more mental processing than you'd expect, just to make sure you don't trip on your own feet. E.g., here's a study showing that even very slow walking (1.77km/hr) prevents you from typing quickly on a cell phone: http://dl.acm.org/citation.cfm?id=1085798

I'm not questioning the 'exercise makes it harder to do some tasks', as your example shows, this is pretty much a given.

But it's not so much about calories, it's about brain workload, walking requires a mental effort that subtracts from whatever else you're doing at the same time. More glucose won't help.

And if typing is difficult, what to say of activities requiring fine motor control, like drawing. They're almost impossible!

Not to mention the insulin/glucagon system controls blood sugar very precisely, you'll rarely have a lack of glucose in the sugar unless you really exercised a lot

> E.g., here's a study showing that even very slow walking (1.77km/hr) prevents you from typing quickly on a cell phone

Isn't that because you're looking at a screen and can't see where you're going? :p

I would count that as a definite factor (not having read the study), but, I can imagine that even without the screen, people walk slower when typing, as concentrating on the words is distracting a faster walk.

Do you have any information to indicate that this kind of cognitive interference is due to glucose depletion?

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