Tony Mangan,
the Irish ultrarunner, whose goal is to run around the world,
has come up here before. I don't know if any APer's have been following, so I thought I'd point out what he has done thus far as it's worth pondering. He ran in the Dublin marathon in Sept., 2010, then flew to St. John's, Newfoundland in November and thus far has run from there, across the US, down Central America & now the length of South America, recently arriving in the world's southernmost town, Usuhaia, Argentina. This was 596 running days, 25,140km, averaging about a marathon a day - with a high of 75 km, at 55 years old!
From South America, the route goes on to Fiji, then NZ, OZ, up the Malay peninsula thru Asia & Europe with a plan to run in the same Dublin marathon in 2014. His succeeding in running from St. John's to Usuhaia suggests he might make it. I find his blog accounts to be interesting/educational and inspiring. One can ponder the resiliency of his musculoskeletal and cardiovascular systems or the psyche behind it all. Maybe some day should such and such a number of miles run seem more than enough, thinking of his running will be worth a few more.
His records/personal bests