I also sugested something about stamina somewhere, but can't find it anymore. It came down to this:
give every player a background stamina. This is the level they go to when playing some minutes (no 48 needed, no 24 or 5, just some minutes, the more, the faster he'll get back to his background ofcourse)
then, additionally:
training him in stamina regularly will bring him faster up to his background if he is below and drop slower if he is above (or even stay above if he trains stamina often enough), also overtime he will be able to increase his background, if he trains enough stamina.
If he never gets training, or to few training on stamina, he will drop to his background form, and later on can get below it (but decreasing very slowly) If he gets below his background by lack of training, and he does not receive training within let's say 2 weeks, then his background will also decrease.
This way stamina still can go up and down, depending on training, but the player retains some baseform of stamina. In ''extreme'' circumstances this baseform can also change, but normally treated players will keep their background (as people in normal life do as well I guess, some are more atletic than others....)
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