You can build up the cardio REALLY fast though. When I started rowing, running 5 km was pretty rough for me, but after a month of training (rowing 10 km a day and running almost the same), I was able to do a 10 km row, and then do a 10 km run at a faster pace than I originally ran the 5 km at, be joking and laughing the entire time with my crew, finish, and be breathing perfectly normally. Heck, back then, I could probably do 25 km without breathing very heavily at all, and do it at a pretty decent pace too.
I haven't run in a while, nor have I rowed, but I'm gonna start back up this week. I hope my scores don't embarrass me too much as you seem to lose it twice as fast as you can gain it
