What is 100% fit? I don't think in reality there is such a distinct mark, as though a player gets to a certain level and then the management tick a box and say "congratualtions, your a 100% fit."
The whole argument about them being professional athletes is also a slight misnomer, whatever a player's level of fitness you would ask them to go out and give it their all in a game, to push themselves to their maximum limit. If you push your body to the limit, wherever that limit might be, it's going to take it's toll on your body and you are going to need time to recover. Three days isn't necessarily that long to recover if you really push yourself hard, on occassion i've drank too much energy drink at the gym and gone crazy with intense two hour training sessions, i've still been aching 5 days later.