IM race by HR - need advice

Typical IM pace is high zone 2 low zone 3 all day (faster on hills, recover on the downhill and back to plan). You will probably find that it is hard to track it too obsessively as the race goes on, but you should know by now what the feel of high zone 2, low zone 3 is. Let me look at your logs quickly.

I targeted keeping my HR in zone 2 (under 145 for me) the first half of the bike. This is hard to do as it feels too easy, people pass you, etc. Then targeted sub 150 on second half. I looked at my HRM 100 times and slowed down, hard to hold back when you're feeling good. I targeted 155 on the first 13.1, and was steady. The second 13.1 I was very tired and worked hard to stay above 140. All told I had a successful race. I did not 'over cook the bike'. I ran the whole 26.2, though I slowed in miles 18-23. In any marathon, mile 20 is half way.

To arrive at the start of the MARATHON ready to run, you must go at what feels 'too easy' pace on the bike for two reasons:
to save some leg strength, and
to allow your digestion to work so you can get energy from all that food you're eating.
Too hard on the bike = walking on the run.

Race how you've trained. 1 week before the race isn't the time to try something new.

Understand that race day stress may be "different" than training days, so you may see your HR a couple beats/minute higher for the same perceived effort. While your heart may be fine with the extra beats, your stomach may not, so be willing to throttle back to keep your HR in check. If you feel good half way through the run, let the horses loose. Once your GI system is jacked up, it's almost impossible to get it back to normal.

B2b full is going to be my first IM. I've trained with Hr race strategy. My max HR is 185bpm. The whole bike I want to stay@70% or under 130 bpm , first 1/2 of the run 75% under140, next 10 miles 80% under 150, last 5k whatever i can stand. This might sound low to some, but I've done long bricks this way (100 bike/13 run) and felt pretty comfortable. Hope this helps.

x2 on this. Also having my first full IM in 2 weeks at IMFL I have to ask, how during your training can you have you not figured this out? I don't mean for that to come off rude, as I've never looked at the training plan, but weren't you doing long ride/runs at "IM pace"? Best of luck on your IM

No offense taken. I dont think my plan has mentioned "IM pace", rather it has told me which zone(s) to stay in... anywhere from zone 2-4. Some of my long rides averaged high zone 3 (lots of hills and heat here in TX). The plan has been pretty specific about what to do in WO's and I've done well with it. But, it gives no advice about race day. So I'm a bit lost b/c I've been following the plan but it doesnt give me any direction about what to do on race day...

I trained by HR and by pace and occasionally pushed harder on group rides during training. I did not got solely on HR at all in training.

I've not completed true max HR testing but I'd guess mine is in the 180-185 range. My coach's target for me was no higher than 135 HR avg on IM bike and no higher than 150 HR on IM run. I did pay attention to avg speed and avg pace on the bike but I also made sure to manage my HR. I had my 910 set up to display current and avg HR on one of the screens so I could watch it easily. I nailed my avg HR on race day (135 avg on bike, 151 avg on run). I felt good on the bike but was ready to get off the bike starting around mile 90. I felt great on the run (except the last 4 miles). I was able to run almost the entire marathon - I walked most aid stations to make sure I got in fluids and nutrition as well as ice/cold sponges to keep cool. I started running immediately as I approached the end of the aid station. I only had two extended walk periods beyond aid stations and that was in miles 22-24. I went into the race expecting to be sub-13 with a stretch goal of 12:30 if everything went well. I ended up sub-12. Execute your plan and don't get caught up in who is passing you, especially on the bike. If you are patient, you'll probably pass a lot of those same people within the first 10 miles of the run.

Good luck!

By now you should know how your heart rate behaves on your longest training rides, runs, and bricks...think about how you've felt at the end of those sessions and what your HR was.

Thanks for all the replies everyone. I have really enjoyed training by HR and I feel it's going to help me a lot in the race. Again, it's not like I don't know what I've done in training... I guess I just would have liked for the plan to give me a recommendation or some direction on race execution. Since it didn't, I decided to ask everyone here.

Here's some more info in case anyone else would like to give me their suggestions:

I have a really low HR for my age (35). I only broke 150 a handful of times and hit 160 exact a couple times. I'll definitely be trying to gauge other factors (like RPE, speed, etc), but I plan on using HR as my primary pacesetter. I've trained in the Texas heat, which has been brutal at times. So, no practice in cold weather. And we've got lots of hills and trees, so there's been no way for me to practice flat and windy... except on the trainer with a fan blowing on me... ha! So, I am trying to think through all this and how it might affect my HR.

For example, I've done lots of long rides w/ an avg HR of 130 (in the heat, which I'm guessing increases HR). So, since I'm racing in cooler weather, I'm thinking of backing off a bit to around 125 avg HR on the bike... guessing that would equal the same effort since the heat is not there to increase HR.

Another factor, since there are no flats around me, I haven't got to ride constantly pedaling... It's pretty hilly around here and during training, I would have to coast down hills in order to get HR back to the plan recommended zone. Of course, this break allows oxygen to my leg muscles and helps them recover. I wont have this in the race. However, I do have the added fitness of climbing hills, so maybe it will be a wash...

And then there's the wind (if it's there and I hear it's pretty much a certainty at this race). I've never rode in wind for 70 miles straight (what they had last year). But I think HR will help me decide which pace is best...

And before anyone says it, yes I know, I need to just buy a power meter... ha!

Thanks again for all the replies. This race means a lot to me and I want to get it right...