I'm curious to know how hard it is to focus on a concentration intensive task such as programming (or novel writing in the case of Neal Stephenson) and walk at a reasonable pace on a treadmill; not to mention how do you effectively type on your keyboard?
I personally feel like I wouldn't be able to write software while on a treadmill as I already find it hard to do sometimes while standing up at my desk.
Yes, this is the major problem with OP: daily miles logged and a gait problem are some basic preliminaries, but ultimately are irrelevant to the question of whether one should use a treadmill desk and don't really mean anything.
If one doesn't have that specific problem, should one use a treadmill desk? Dunno. He presents several graphs of daily mileage, is that evidence for or against usage of treadmill desks? Dunno. The calorie count is small (compared to what?) when he calculates out, does that mean treadmill desks are not helpful? Dunno.
More relevant would be stuff like: how many emails did he send each day correlated against mileage? How many words did he write in his novel, or how many words did he edit? Did he at least lose some weight? Was his mood better on treadmill days? Did he consider running a simple randomized test (just flip a coin for each day whether to use a treadmill) for anything? Heck, what was his subjective experience, even, about the effects of treadmill - did he feel unable, as many people do (not just you), to do anything requiring real concentration?
OP reminds me a lot of Stephen Wolfram's big fancy QS post about metrics like typing: he had measured an impressive number of things, but nothing that ever mattered.
I assumed at 3mi a day he's walking for about 1-1½ hours and so was doing that at times when he's normally be reading back work, dictating, reading forums or watching a video or what-have-you.
I personally find it difficult to do anything mentally taxing. I walk at a 3.5mph pace, and I can hardly stay concentrated. I can code and do grunt work, but I can't solve complex problems while on a treadmill desk.
I find a solution in splitting my time and do complex coding while sitting grunt coding while on the treadmill. The switching is distracting. I don't get as much done this way comparing to sitting all day, but overall I think the health benefit is worth it.
There is also the possibility my pace is too fast, though.
I personally feel like I wouldn't be able to write software while on a treadmill as I already find it hard to do sometimes while standing up at my desk.