BT Forum

Well, z2 is not 'very easy' -- that's z1. But I would say that z2 is an effort that you feel you could hold until non-muscular limiters (joint pain, general pounding) become an issue. I.e., my view of z2 is that having to stop or slow down while running z2 has more to do with pain and pounding than it does with muscular (and certainly aerobic) fatigue. FWIW the percentages that I use would put the lower end of your z2 a bit lower more like 153.

As for the upper zones -- it is very difficult to use HR as a guide at the very highest zones like 5c (in the scheme you use). The amount of time spent (if any!) in that zone during training is so small that you might not actually get your HR up that high even if you are doing the appropriate effort, because of the delay between effort and heart rate.. For those efforts (workouts such as 400 and 800 intervals) you are much better off (IMO) using pace and maybe RPE if you have that dialed in. But I'd also emphasize that a lot of things need to be in place before training at that intensity even for short periods of time makes any sense.

When in doubt do the test!

Race efforts are typically higher than what you would see doing the test. IMHO your LT is a bit lower.  Did you read the article that came from the thread? There's a chart at the bottom of it correlating HR zones and RPE.