Originally Posted by
NathanC
I probably only get to about 30km in a trainer session. The intensity is what I measure on a trainer.
Then HTFU if you need to. Folks routinely do ironman training 5-6 hour training rides on an indoor trainer. (Surprisingly commonplace - hang out on the tri forums and see all the Midwest folks snowed in all winter but prepping for a March-Apr Ironman.)
Of course, if you reserve your long stuff for outdoors and intensity for trainer, it's all good.