Why do cyclists/swimmers require so many more hours than runners? It has to do with efficiency.
Efficiency of cycling is around 25%
Efficiency of running is around 40%
(40%/25%)^2 = Phi^2 = 2.618
Thus, 10 hours of running in a week is generally equivalent to about 26 hours on the bike.
A 2 hour time trial running (elite marathon) is equivalent to a 5:15 time trial on the bike (omg that would suck sooooo bad). Makes sense that elites tend to do only 2 big marathons a year. I can’t imagine doing a 5ish hour time trial on the bike more than 1-2X a year.