There was a time in the NBA when a coach had to pull a player off the court with the jaws of life. Regardless of the team, players wanted to play, they wanted to play all 48 minutes, and they wanted to play all 82 games.
Although I cannot cite this because I only know this story second-hand, I am told from a very reliable source that when asked once about exhaustion following a particular game, Larry Bird stated that he could play a double-header no problem.
That was the point of view from a superstar who for the last few years of his career literally played with a broken back.