I've noticed, correctly or not, that my high stamina players can play more minutes and keep/improve gameshape than my low stamina players. Haven't seen any studies on this and it could just be a coincidence.
And other players just seem to be a pain to keep high GS no matter how many minutes you give them. On the flip side, my 35 yr old guard spends almost every single week at proficient and rarely dips. There's definitely some randomness from player to player in that regard.