Claudius Claudius You said he didn't break Saka.
I don't think there's a common link between injury, rest, and fatigue that applies across the board. It seems to come down to individual players.
Salah played almost every minute of Liverpool's league campaign last year, as well as Champions League and Egyptian games, though didn't play many cup games. He's probably played similar in years gone by without injury. Saka on the other hand does not appear to cope well with the load. There may be other reasons, but it appears on the fact of it that he's in a more physically demanding role in Arteta's system than Salah was in Klopp's or Slot's. Saka on the other hand seems to have a problem with muscle injuries which suggests he might need a greater element of care and handling than Salah, who's body may just be more physically robust. None of us know for sure, and Arteta will have all the data he needs at his disposal, but it's hard to say we're managing him right when we know he has problems with certain types of injuries, yet continue to play him through opportunities where we could rest him, either by benching or subbing him.