Purely unscientific, but I've done 1 century and 3 marathons. How I felt after the century and the marathons was similar. I've done many half marathons and while I've never gave it much thought, I guess I guesstimate a half to be about 55 or so miles on the bike. One thing that is common to all those activities is I usually enjoy a beer afterwards.
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"It is the unknown around the corner that turns my wheels." -- Heinz Stücke