This is an old post but I am also having some confusion with this plan.

In the book he refers to the zones being a percentage of maximum sustainable heart rate. I did my two 3 miles time trials and managed an average HR of 168 for both efforts.

I am customizing my Garmin Edge 500 to fall within his zones, but it seems that going by MSHR makes the heart rates of these zones pretty low. I mean if zone 5 is supposed to be an all out effort, Carmichael has zone 5 as +94% of MSHR which for me would be 157-158bpm and that's only 85% of my max HR. Those numbers seem way to low, am I missing something?

The chart he provides for training zones follows:
Range, %MSHR
1, 50-70
2, 50-91
3, 88-90
4, 92-94
5, 94+

Zone 2 runs over zones 1 and 3 which I don't understand, there is nothing for 90-92, so I setup the training zones on my garmin as follows.

Z1 - 50-70
Z2 - 70-88
Z3 - 88-91
Z4 - 91-94
Z5 - 94-100

So I guess thats ok, but again the low heart rates by doing it all based off of MSHR annoys me. I don't feel like I am doing whats right and im confused. Carmichaels zones are frustrating me.