Since I suffer from MS, I have long periods I can't shoot. Frequently even for 6 months. I am always afraid my form will suffer, but that is not the case. After some sessions, like three to four, I shoot like I have never been away. Most of the times I even come back stronger, like I got rid of the bad things in my form but kept the good ones. As for muscles, and fatigue, I start with a session of 50 to 100 arrows and am soon above the 200 per session. I train 3 times a week when I am healthy enough, and always keep one day in between to recover.
I can shoot Robin hoods at 30 yards and hit a balloon at 60 yards, that is how my normal form is. My bows are between the 45 and 51 lbs.
Best example is that in spring last year. I participated in a big and difficult 3D tournament after fighting a bad stroke for 5 months. I trained only three times one week before. Reason to participate was that it was a very short drive. Went there, expected nothing and won the first price. Had to fight my tears when my name was called and I came forward to recieve my price and the applause....
But it is not like riding a bike, because I can ride a bike without hands