The prizefighters of the 18th century fought in a kind of style that would more closely resemble MMA, but with no gentlemanly opportunity to tap out to a joint lock or choke, but instead a non-stop dirty-boxing and throw-heavy war to unconsciousness.
Still, the old-time fighters were most certainly sportsmen and professional athletes, and their training was taken as seriously then as it is now. In The Heavyweight Championship, Nat Fleischer quotes an article from Boxiana, the Georgian era's equivalent of The Ring:
The skilled trainer attends to the state of the bowels, of the lungs, and the skin; and uses such means as will reduce the fat, at the same time, invigorate the muscular fibres (sic)...he is sweated by walking under a load of clothes, and by lying between feather-beds. His limbs are roughly rubbed. his diet is beef or mutton: his drink strong ale...(He) enters upon his training with a regular course of physic, which consists of three doses...he must rise at five in the morning, run half a mile at top speed uphill and walk six miles at a moderate pace, coming in about seven to breakfast, which should be beef-steaks or mutton chops with stale bread and old beer. After breakfast he must again walk six miles at a moderate pace, at at twelve lie down in bed without his close half an hour...on getting up, he must walk four miles and return by four to dinner...Immediately after dinner he must resume his exercise by running half a mile at top speed , and walking six miles at moderate pace.
Under the rules of the day, which required a fight to the knockout, surrender or collapse, all that road work made sense. In a very long fight, simply staying upright and paying attention could become a problem after an hour or so. As a former infantryman, I can tell you that a walking regimen like that day after day is going to force your body to get hard quick.
Or else break it.
Without a modern sauna to employ, the historical trainer's desire to keep the muscles warm and the body sweating and limber is smart.
I do worry about this fighter dehydrating, but the prescription of strong ale is not as bad an idea as it sounds. Alcohol is a muscle-relaxant, and a heavy ale is a legitimate source of carbohydrates, something that an athletic fighter would burn up while walking 20 miles a day.
Prizefighting has always been a thinking man's sport.