Originally Posted by gregf83

Forgetting about the numbers, the description for zone 4 from your chart is the mean HR from a race. This is not easy for anyone. If your zone 4 pace is 'super easy' then you likely have your zones calibrated incorrectly. It has nothing to do with conditioning. As your fitness improves you'll go faster but effort in zones doesn't change.

In general it's better to base your training on LTHR rather than MaxHR. Do a 30 min interval all out and the average HR in the final 20 min will be pretty close to your LTHR. This is not easy for anyone from beginner to pro. It matches zone 5 in your chart.