Originally Posted by hhnngg1

I'm currently an active triathlete. I run about 35 miles per week now and bike around 6hrs per week (distance irrelevant as I'm indoors the whole time now.) I also swim (badly). Was an ex-pure marathon runner, have run marathons at 3:11 pace about 7 years ago, and am not too far off that now in terms of shape.


I think it's up in the air as to which one helps you be better at the other and depends HEAVILY on how hard you worked at it. I've seen ex-pure pro cyclists run sub-3 marathons on very little mileage, and I've seen ex D1 runners become bike monsters in a matter of 2 weeks.

But to generalize for the overall populace, if you're not dealing with competitive road cyclists going to running, typically runners will have an easier time with cycling and be faster because the weight bearing and pounding of running limits keeps a fairly decent minimum threshold on training, whereas on the bike you can really take it easy if you're not a racer.

The leg pounding is a big deal. If I had to only train 1 sport for triathlon, it would definitely be running, as you can easily fake your way through a 56, even 100 mile bike ride with nothing but run training, but you will not be able to fake your way through a HM or marathon if you run zero miles in training.