[ctchocula]

I like how you describe vo2 max as similar to an xp bar, because I've felt something similar. Zone 2 is what got me into running, because it made running not hurt and almost pleasurable.

It's much more sustainable than Zone 4 (supposedly anyone can maintain Zone 2 for hours) and brings with it a bunch of metabolic and health benefits. I found the book "80/20 Running" to have excellent running schedules for how to mix in a small but appropriate amount of fast Zone 4 running into a schedule that's predominantly Zone 2. It has a good mix of intervals, tempo runs and hill runs that build you up to run 5k, 10s, halfs and full marathons in beginner, intermediate and advanced pace goals.

The intent of the slow Zone 2 is to build the cardiovascular base that gives you better aerobic endurance without stressing your body out too much. Zone 4 is what makes you faster.

[johnfn]

This is an old response, but thanks for the comment. I feel like you articulated zone 2 a lot better than almost anywhere else I've seen.