Originally Posted by
McBTC
It's probably a debate in itself as to whether running a marathon and cycling a century are roughly equivalent but I can't think of any exercise that tops the TdF, requiring on average about a century a day for weeks-- even so, the fact some can compete at that level probably is because it probably would just beat the body up too much to run (race) on average, a marathon a day for 21 days over a 23-day period.
There are male and female marathoners and ultra runners that have done the 50 in 50 and 60 marathons in 60 days, Dean did this running each of his back to back marathons in different states. Obviously, the logistics are insane, but they weren't racing. The Self-Transcendence 3100 requires about two marathons a day for a couple of months, and they are racing. Bitter ran 100 miles in under 12 hours. There are plenty of such examples.
Unless you are shooting for a remarkable finishing time, I don't think a century is particularly difficult. Add racing, hills and speed, then sure. TdF?, crazy.