Yes and no. You just spend very, very little in Z2 (or none at all, which is never going to happen in reality.) It has become a bit of a misconception and people often mix POL up with exclusively being 80:20 training, which is not the case ( I think I did that recently, or a least inadvertently made a comment that would have supported the belief that POL=80:20 when I didn’t mean too.)
When I originally heard about the concept of POL a common distribution discussed in the three Zone system was 80:20 and 80:5:15
But these weren’t the only distributions, there is also 90:10, 95:5 which happens to be where my running falls
or even 85-5-10 but for some reason, maybe because a few popular books and book titles people seem to have gravitated to 80:20 being ‘the one’
I picture it like a distorted or mis-shaped egg timer, with the bottom half 70 - 90% the volume and the top 10 - 30%, but the reality is there is that thin bit in the middle (Z2) where the sand trickles through.
Interestingly if you tip the egg timer upside down you get inverse polarised, not that I have ever heard of anyone training like that.
Mainly muscular endurance, ‘lactate shuttling’ and reduction in VLamax.
Ref: Polarised Cycling Training: A Detailed Guide — High North Performance