A *long long* time ago we had a pretty good thread concerning how long a stud session could be played without becoming tired and making costly mistakes. Some online LHE players assumed they could play many hours or even days. Stud players weren't so sure. I always felt that stud high (played for good stakes) couldn't be played by rote and required unwavering attention.
Here's an op-ed from the NYT that points to some research studies that can help you the next time you go to the doctor, ask for parole, or buy a new car. Also play stud.
Don’t Visit Your Doctor in the Afternoon