I heard Tim Bradley say he would run 8-12 miles a day. What other boxers commonly ran 10 miles or in that neighborhood.
I read that Marciano used to run 9-10, and upped that nearer the fight. Also expecting a comedian to come and say Mayweather...
The literal answer to this question is probably Peter Maher. He was a standout, in an era where extreme roadwork was the norm. A 20 mile training run was just part of his routine.