If you save in career mode, exit and then reload, all your player's fatigue levels will go down. You can do this multiple times in a row and raise there levels into 85-100% range. It's pointless to do it if all your players are over the 85 mark though as it just as often seems to make the % go down as up..

This is a great bug if you find your team drained and you've been focusing on other upgrades...

Hmm, I hadn't noticed that yet. I'm not one to exploit a bug like that, although I do sell players to see who I can get and then reload it to sell other players to see if there are better options. I'll look into this bug when I get home. Thanks for the tip.

I've noticed the bug too.

That's good i'm not going to worry anymore about wasting upgrade points on a fitness trainer.