I often work standing up. One thing he missed, probably because he uses a laptop, is that it is more comfortable when standing to have your keyboard quite a bit lower than your monitor. For some reason, it feels more uncomfortable to me to have my elbows bent as much as would be necessary to have the keyboard directly below the monitor. I have my keyboard at about 42 inches (navel height) which is also where I have my fine assembly workbenches (for electronics and other small work). My monitor I have raised higher, with my eye level about one-third from the top of the screen. Footrests do help, but I just have file boxes around that I can rest my feet on when needed.
Hmm, seems like this writeup is missing the vital recommendation that you have a foot rest and alternate between elevating one foot, elevating the other foot, and having both feet on the floor. I've tried working standing up without a footrest and found it intolerable after a short time, but with alternating feet height I can work standing for extended periods of time - and me feet/knees/back are happier than when I work seated.
I have been trying to work on a treadmill for the last 2 days. The platform shakes, the motor is noisy at low RPMs and so far isn't sustainable for a long period of time.