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.
I guess its relative to the person, how you handle pain and what really gets to you. I personally feel like I've adapted the feeling of being in that zone as my natural fast and steady zone. I'm not exerting myself to a point that can't be sustained over long distances. Zone 5 however gets into the area that can only be sustained for short distances and leaves me needing to recover for a few second before I can mellow out in my 4 again. I tend to thing my pain tolerance is pretty high but I just don't think that 4 is anything to feel super tired over unless you've steady stayed in that zone for something like 2 hours.