ok i threw 110 haymaker in 4 minutes of action before I KO'ed Pacman.....each haymaker missed or connected took a good deal of stamina but it was temporary, and not full lasting. So by the end of the 1st round after throwing 70 haymakers and connecting at around 50 percent, my stamina was back to 100 percent.
edit: a missed haymeker takes a bit more stamina off, maybe 30 percent more eyeballing the bars, but then again, after 70 haymakers in round 1, I shouldn't have 100 percent stamina right?