How did you determine these zones? Are these zones based off threshold hr or max hr?
Based on your zones (assuming they are accurate), I think you need to be floating around low zone 2. Like under 155 hr. Anything more than that for an extended period of time will not lead to good results on the run.
To be honest I am not entirely sure how my heart rate zones were calculated (my coach did it based on all the data I supply him). I agree, my problem was that if I were to ride under 155 bpm (my goal was 148 bpm) I would have been no where near making the cut off. I feel very fortunate that I was able to keep my run going for the entire marathon after that bike, seems like I kind of dodged a bullet there.
Would you mind sharing your run and swim times with us??? It seems odd that you were able to swim very easy, then bike apparently pretty hard, and yet still run the whole mary. Most people who have high HRs on the bike pay for it dearly on the run. To me it is kind of amazing that your HR kept going up during the bike b/c for me once I start to get pretty tired, my HR starts going down, simply b/c I have very little glycogen available to fuel a faster effort. You are an unusual case. :)
I swam a 1:41, biked the 8:15 (yes it felt like a very very strong effort) and ran a 5:55 (which for me is not a bad pace for a run of that length, my stand alone marathon PR is a 5:41). My average HR on the run was 146 which I was pleasantly surprised with. I kept waiting for my bike HR to catch up with me on the run and make me pay but it didn't really come.
Well, it seems like you had a really good race, with an appropriately easy swim, a strong bike and a strong run. It is a bit unusual IMO for your run HR to be less than your bike HR but this may be reflective of your just getting tired as everyone does in the iron mary. Also, based on your HRs, it seems that your max HR must be pretty close to 220. As others have suggested, try doing an all-out 1 or 2-mi run, pushing it all out at the end, and see what your HRM says. Of course, you'll need to recover for 3-4 weeks before attempting this. :)
"Anyone can be who they want to be IF they have the HUNGER and the DRIVE."