Never saw Bret or Shawn blow up, even during their Iron Man match. Jericho was another who never seemed to get gassed in the ring. But even Bret said it in his book, Flair had unbelievable conditioning.
I heard Flair say he would do 500 squats every morning. He also said the routine at Verne Gagne's school was to run 2 miles then do 200 squats.