race pace

According to D3, IM's should be run in Z1/Z2.

That being said, most workouts in my BT plan have me doing Z1/Z2 sessions, which is right at IM pace.  Here is the link:  http://www.d3multisport.com/articles/idealHR.htm

If it were me, I would do a recovery run for 70min, then high zone 2 for 20.

Don't take anything I have to say as gospel, but I think Z1 only for an IM is too slow.  I think you could/should go faster...  Again, that's the theory I have been following, and it seems to be working out.

I'll be working on some Dr. Phil Maffetone training methodologies to prepare for next year's IM Moo, and Z1/Z2 is accurate.  It may seem slow, but it's all about endurance, correct?  You are building your body to run faster but at the slower heart-rate.  It takes weeks, if not months to do, but the reward is worth it!  Part of this process allows you to be less injury-proned, too.

I followed his research for a long time, so I'm familiar.  After years of playing around, I think that LT method gets my Z1/Z2 where I think it does the most good for me.  They are sort of close.  180-age (+5 for training) has me at 145.  LT has my Z2 is 143 to 153.  I like keeping my training at about 143-145, so close to maffetone.  I don't mind at all if it gets up to 150 or so during a ride.  If I hit Z3, I try to dial it back some. 

HOWEVER, with my run, Z2 is more like 153 to 163.  I feel great during long runs at about 150-153, but don't mind going at 158 for a while either.  I think the 145 for the run is a little slow.

Regardless, I too have made some great gains by training a lot in Z1/Z2.  It's all about the same.  I plan to race Z1/Z2 as well, since I know I should be able to sustain it.

I just think that restricting yourself to Z1 for a race, would leave too much in the tank at the end.  But that could just be me.

Have you calculated your VDOT?  Are you using a GPS device or do you have markers or a track you can run on to monitor your pace?  HR is helpful, but I don't believe it is what your plan expects you to use when it says: "race pace".  That is usually a specific speed that you are supposed to run that you should know from doing various running tests or from races of various distances.

I found this thread to be really helpful in helping me figure out where I should be:  http://beginnertriathlete.com/discussion/forums/thread-view.asp?tid=125326&start=1

I have also used the pacing calculator at RunnersWorld.com: http://www.runnersworld.com/cda/trainingcalculator/0,7169,s6-238-277-279-0-0-0-0-0,00.html