I have experienced two factors which make typing slow and/or hands fatigue. The obvious one is finger movement, anyone agree here. But there is also tension in your muscles which contribute significantly to fatigue and health problems.

Any time I wish to could turkey any new or not used for long keyboard layout I am aware of additional tension so I do it cautiously. But with Dvorak and Qwerty it seems to wanish completely whilst with Colemak still I cannot overcome it. Currently I am stick to this layout and even started to "feel it" how well it performs in longer text. Hovewer just recently I have got burning sensation in my hands. The vains become clearly visible in blue under the skin. Of course I kept off the keyboard for the whole weekend. I am still thinking why this happened. It seems for me that my muscles keep certain level of strain because I force them to stay constantly on the home row. Whilst it is merely the same with Dvorak layout, maybe the frequent hands alternation on the latter help to release the tension. I do not know for sure yet.

The comofort position on the keyboard for me is to keep pinky and index finger on home row but ring and middle on top row. I will try to make more frequent brakes from typing at work and keep my hands comfortably on the keyboard when not typing (instead of keeping them on the home row constantly).

I am not trying to put away anyone here from trying Colemak but I see it worth to warn you to keep an eye on how your hands feel. I will update what happened with my hands in the following days.

As to how much I type factor: I was trainning everyday for 30-40 minutes, average 47WPM; at work I am coding so it is hardly ever constant typing.