I have to admit that I flip flop on this one. I work part time in construction (brick layer) with a group of guys that make it a horse race. I can get out there and keep up with the best of them for 10 hours or more a day. However, when I'm not working and trying to get things done in an office environment that just wracks me. I get stressed and fatigued and rarely get anything done worth a dime. It can take me 4 hours to write up some business stuff that I could have written in 45 minutes back in the better days. And 6 hours in the office creates such mental fatigue that I just want to go home and veg on the TV.