I've played like 6 or 7 sets of doubles in a day, but those are mostly casual games.
On the other hand... there is no way I can even run 5 miles. The last PFT I had I struggled with the 1.5 mile run.
My physical fitness level is very poor for someone with such a high energy game. If I dont put my 100% of my body into every shot my results go dramatically down. I'm at the point where just muscling the ball around the court with bad footwork and prep greatly reduces accuracy.
I need a much higher level of physical fitness. I just dont work for it.
"In the 1980's two men dominated--sometimes each other, most of the time everyone else."