Na man... You get like 2-3 days to rest before the semis. Not to mention rain delays and bullshit. These guys are pro athletes for a reason. Everyone makes way too much out of fatigue and shit. It's more mental fatigue when you play Nadal or Fed that gets to you. and ppl are under the illusion that it's physical. It's not. It's just they feel defeated in their head, and their legs stop working, stop moving.