Well, I may have played 8 hour marathons, but I still took a long time to beat the game (old gamecube version). This is because I died a LOT, and I love to look around and explore. This game also had me really just standing still at some parts to marvel in the beautiful graphics (furnace room anyone?).
As for the arm thing, I play moving my whole arm while laying down, and as my arm begins to tire, I do rest my elbow on my leg, the floor, a pillow, etc. But even then, I'm still moving more than just my wrist, so I can't do 8 hour marathons. (I can do 4 hour marathons instead.... and since I've already played through the GC version, no need to explore.)