Hoping with your collective experience you can help me out. I've been trying to train with a heart rate monitor recently rather than relying more on 'feel'. My problem is that while running, my efforts / performance don't seem to correlate to the correct HR zones. For example, on my longest runs (2 hours) over a fairly flat course, I'll average 159 bpm and feel like I can keep going at that intensity. Now, based on a Polar predicted max HR of 186 (yeah, I know this can be inaccurate) I've just done a 2 hour run at 159/186, or 85% of max HR. From what I've read, this would be zone 4, and lactate threshold intervals. Huh? Am I a freak?
As for keeping my HR in zone 2 (about 140 bpm) - forget about it. I'd have to walk, not run.
So, what do I do? Ignore my HR, and go back to training how I was before? Slow down (walk)? Read a different book? Out of interest, while cycling my HR zones seem to correlate quite well (albeit using the rough -10 bpm per zone theory).