I think if you're able to ride year round your core will adapt to what it needs to. For the past 13 yrs I've been pretty consistent at 500-600 hrs/yr with at most a couple weeks off for various reasons. I used to get a tired/sore back at the start of Ice Hockey season but that was because there was a sharp transition from no skating to playing a couple times a week. If you don't cycle or cycle significantly less in the winter then perhaps you might get a sore back when ramping up but I don't see it happening if you ride steadily during the year.