By Jennifer Quinn
BBC News Online Magazine
Brown lost two stone on the 71-day run, pasties notwithstanding
Vomiting, the shakes, diarrhoea - all delightful after-effects of running ultra-marathons. The human body isn't built to run 50 miles a day, but that doesn't mean no one will try it.
Bob Brown finished a 3,100 mile race across the United States fuelled by the three Ps: Preparation. Perseverance. Pasties.
He describes himself as a laid-back primary teacher who enjoys life in Cornwall with his wife, Amy. But his biography reveals something else about the 35-year-old: "I just cannot resist a challenge." And he has, in the past, described himself as an exercise junkie.
So the fact that his name was among the dozen entrants in the Run Across America makes sense, even if the idea of running nearly two marathons a day seems ludicrous.
Fuelled by Cornish Pasties and competitive fire, Mr Brown was the first to cross the finish line in New York's Central Park nearly 511 hours - of running - after he first set out from southern California on 12 June.
That makes more than eight hours and 43 miles a day. Hard? Certainly. Sensible? Debatable.
Forrest Gump did it
"It's not a natural level of activity," said Joe Dunbar, a sports scientist and physiologist.
"It's something you have to prepare for. It's not something you could complete without a hell of a lot of training, and you just have to spend a lot of time - weeks and months - of preparation and building up time on your feet."
POINTS OF PAIN
1. Heat exhaustion
2. Burned lips, tongue from acidic vomit
4. Intestinal upset
5. Nerve damage
6. Lost toenails
Lloyd Scott, who may be most famous for running the London Marathon in an old-fashioned diver's suit, has also competed in ultra-marathons and describes the after-effects of those endeavours as debilitating.
Mr Scott, a cancer survivor who has dedicated his life to raising money for good causes, ran 135 miles through California's Death Valley in just under 60 hours.
"When I finished Death Valley, I brought up my stomach lining. It was all acid. I burnt my tongue and lips. I lost three toenails, had heat exhaustion, nerve damage to both feet," Mr Scott recalls. "It was extremely brutal on the body."
"Every part of me just ached."
Extreme athletes are constantly testing the limits of their bodies and can be hovering on the "knife-edge" that separates injury and illness from optimum health.
"It's over and above," Mr Dunbar says. "You often hear of athletes talking about being on the knife edge, of having a certain amount of fitness that takes them way beyond healthy, and then you can take it that little bit too far - for athletes, it's in terms of intensity - that can lead them to illness and injury.
Pain, at what gain?
"It's just the sheer volume. And the difficulty is in preparing for these, to do enough practice that your body is equipped to do what it needs to do in the event, but not doing too much so that you get to the event exhausted or injured."
The training is bad, but the run itself is also pretty tough on the body, Mr Dunbar says.
"The muscles will be tight and shortening," he says. "The continued impact does leave one very much at risk - the bones, and particularly the joints."
For his part, Mr Scott says he's finished running ultra marathons - though it's worth noting his run across London in a 130-pound diving suit came after that decision, and in October he intends to cycle across Australia on a penny-farthing - because it's just too hard on the body.
Mr Brown agrees there's a definite physical challenge, but says the mental battle fought on the roads is equally tough.
"Obviously, physically you've got to be supremely fit, but I think the main part of it is mentally, you've got to be supremely strong mentally," he told reporters after arriving in New York.
"When you start out a race like this, knowing you've got to run nearly two marathons (a day) in 71 days, I mean that is hard for anyone to take, so it's a constant battle with the mind rather than the body."