Brandt Snedeker wore a device in practice to see how much walking he would have to do this week and the result was nearly TEN MILES per day on this course due to the length, terrain and how the layout is. The days of Craig Stadler and John Daly being competitive are over. All of these guys work out with fitness training routines.
I'd never thought about it that way, just starting to learn about how guys get to the tour, and it's got to be mentally grueling. The number who aren't "on the bubble" is incredibly small.
And yes, they've got to be fit, because even a little fatigue has got to kill the finesse and control needed for many shots.