Just finished a book about Rocky Marciano. From the time he was twelve years old until the day retired he walked- he would take several long, brisk walks everyday. Dempsey walked. John L. Sullivan walked. Many of the old time trainers - Ray Arcel for example- didn't advocate running long distances. Rather they talked about "sharpening" the wind, with a routine that combined walking at a fast pace for a minute (to simulate the between rounds period) and then alternately running and sprinting for three minutes, in random intervals.