Stamina trains 1-2 weeks, most my players staminas are around Inept and medicore, I've read places where it sais if their stamina is low and if you play them too much in a game there results will not come out good...And they will not play as efficiently as they can... Im not too sure about stamina but thats what I've read, all I know is that they will Pop in 1-2 weeks.. ;)