Some people have started using treadmill desks to allow themselves to exercise while they are working. Apparently, it allows them to burn "100 to 130 calories an hour at speeds slower than two miles an hour". I am skeptical though, of the effect on productivity. Firstly, the walking sounds like it would be distracting and secondly typing might be harder (and less ergonomic), when walking. What effect do these desks have on productivity?
It's hard to estimate. I've been using one for 9 months now and can not conclude one way or another due to the constantly varying complexity of my work and other inestimable variables.
I can say though that I'm still walking as much as I was 9 months ago and have no plans to stop. Lack of focus in my job means no pay so I'd stop it immediately if I noticed a detrimental effect on my productivity.
Walking becomes second nature—you don't even realise you're doing it. I don't believe in tracking how many miles I do in a week or whatever as many officewalkers do—I just have it as an invisible part of my workflow, just like sitting on a chair. It still however amazes me when I turn the machine off and notice how many miles I just walked without even thinking about it.
But that's at speeds around 2mph. There's no sweating, heavy breathing or thinking of balancing at such slow speeds. Mouse or keyboard control is no problem at all. Precision graphic work however requires me to jump on the treadmill rails or turn off the treadmill off.
Going faster than 2mph I find I start to become aware of the walking. 3mph is fine for reading technical works, but I found my focus in solving complex problems started to suffer.
Another aspect of the treadmill I like is the beat of my footsteps gives that same effect as the ticking of a Pomodoro timer--it keeps work moving along and makes it feel like you're on a mission rather than just sitting around. It stops me getting too bogged down in a problem.
Maybe healthier body, healthier mind rings true, I don't know--there are too many variables. I'm not overweight any more because of the treadmill so tend to go out more and work less hours, but I feel those hours are more productive.
If you're overweight then you have bigger issues to solve than being maximally productive. It's hard to be maximally productive when you're sick yet again or stressed because of your weight.
If you hate exercise, then this is like giving soup to kids to get veges into them.
I tried working on an exercise bike before the treadmill and I tried a stand-up desk. I found both affected my productivity and made me sore. The treadmill I love.
I've been treadmiling while working for almost two years now. I develop code and run my company on it. I really like it and my experience is similar to the other comment above. I walk a minimum of 5 to 6 miles a day and feel that it works great for me. I am naturally coordinated and athletic so it feels natural. A friend of mine who is also athletic can't do it. He said it was too hard to do both at once. Just didn't work for him. You should just try it sometime. I feel really good. One thing you'll quickly learn is that you need good shoes. I naturally move from the treadmill to a chair with the laptop on my lap as my body feels like I want to (usually because my feet are a little sore). I'd say sore feet is the biggest challenge I have with it and that meant going to a running store and trying lots of shoes to find just the right ones and then switching between them. I have four nice and different pairs. And when my feet are sore, for whatever reason they will be more sore somedays then others, I wear Crocs. Highly recommend treadmill walking if you can do it. Some of the best concentration happens after a stretch of walking when I get off the treadmill for half an hour, say, since I am oxygenated but not sluggish from sitting yet. Once I feel the slug kicking in, time to jump on the tread'. Please take care of yourself. Computing while sitting all day is unhealthy due to sedentary blood-flow and other issues. Your body was made to move. A body in motion stays in motion.
Also, according to Dr. John Medina in his book Brain Rules...our brain benefits from cardiovascular activity 3 times a week (30 minutes each session). This improves our brain's executive function...
In the book he also criticizes the current school system where students spend most of their time sitting sedentary at desks to learn. He proposes more physical activity interspersed throughout the day.