8 - 10 hr days are no problem. I built up to that over a few weeks. Other possibly relevant factors: Switched to dvorak about 10 years ago. I'm in athletic s

8 - 10 hr days are no problem. I built up to that over a few weeks. Other possibly relevant factors: Switched to dvorak about 10 years ago. I'm in athletic shape and maintain a healthfull diet. I usually have a dead tree format book going, and take occasional breaks during the day to read, cook, exercise, take a walk, etc. Footwear makes a big difference. Minimal slippers were best. Anything with arch support makes my feet hurt after a few hours.