The thing I've noticed over the years of being around the running community is that everyone's body seems to have a hard mileage limit. I know many people who do fine at 40 miles a week but fall apart at 50 (I'm one of them). It takes a long time to figure out your own limits, and it usually takes being injured a few times to accept it.
I think that's one of the things that separates running from cycling--pretty much anyone can at least theoretically do the volumes necessary for elite cycling performance, but only a select few can handle 100+ mile weeks of running for very long. Then it comes down to talent etc.
ride bikes, climb, ski, travel, cook, work to fund former, repeat.
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