Originally Posted by guadzilla

Ah cool, thanks for the considered reply.

I used to do 6-8 hour weeks with a fair bit of high intensity but i found that the gains I had then didnt last - but then, I only started endurance sports in my mid-30s (and in my mid-to-late 40s now). Am doing an 80:20 polarized plan with 10-12 hours of bike+run, and am feeling that my foundation is getting a lot better. I also recognize a big improvement from doing long Z2 with very little time in Z2. I suspect that for me, i need to pay attention to the volume each yet and do atleast 2-3 months of volume focused efforts between more traditional intensity blocks.