I couldn't agree more with your first sentence. Sir Steven Redgrave, possible the best rower ever. once wrote that people were always saying to him "Wow, you're so fit, you must feel great and have lots of energy!" but that in fact, training on his level, you're always on the edge of getting sick.
On the other hand I'm not to clear on why I've done 95km on the rowing machine since Thanksgiving, worked on not overeating, and my weight hasn't budged. Neither has my BP, but it's probably fair to assume that my stress level has been on the stratospheric side.