Pete:
I value your data and am not trying to be a pained antagonist. I'm genuinely trying to get a handle on realities. I know from my own experience of tracking my HR max that many people slightly underestimate this figure. Certainly the general formulas are useless; I'm 47 and my current HR max is 196. Two years ago is was 198. The formulas say it should be in the high 170s. They're useless.
I went out and made a test yesterday during a long run on which I wore a HR monitor. I began very slowly (HR 145 or so) but by midpoint had found a steady-state groove at HR 170, which is (I'm without my calculator!) 87.5% of max. I wasn't moving at my imputed marathon pace--I've been training hard--but it certainly felt like marathon intensity. 3/3 breathing rate. At 173 there was a break point and a 3/2 rate suddenly felt right--I'd describe this as sub-threshold but approaching threshold. 177-178 was another palpable transition point and a 2/2 breathing rate suddenly kicked in. So I'd peg my threshold at 178-180, with anything over that slightly above threshold. Call 177, or 90% half marathon pace. Just a tick below threshold
I ran four half marathons last year and I know the feeling of half M pace.
Now, as the run continued and my buddy and I held pace at HR of 170-178, pushing past 12, 13 miles, I pushed a little harder, as though I were actually running a half marathon, and of course my HR went up. 182 seemed to stabilize--the isocapnic buffering zone, if I've read John Kellogg properly. Transitioning into 10K race pace. Sustainable in the 14th mile without much trouble, but clearly over threshold at 1:57 and counting, with some glycogen depletion making its presence felt.
In the last mile, mile 15, I picked it up even more--past 10K race pace--and in the final quarter I sprinted hard up a slight incline, watched my HR hit 195 and then, finally, 196. Maybe one more beat to be squeezed out, on a hot day, but not yesterday, as I felt everything give way. I backed way off and jogged the final hundred yards.
This is the way we run longer races: finding sustainable sub-threshold paces early on, holding them and, if possible, slightly inching them up as we go, then, as we know we've passed the danger point later in the race, increasing pace a bit. I suspect I'm not the only one to run the last mile or two of a half marathon at 10K intensity, as I did back in December
I'm extremely happy with the information I gathered yesterday--particularly the correlations I now have between breathing race transition points and HR, and HR and various subjective feeling-states. I should note that my actual pace at threshold was more than a minute [sic] slower than it "ought" to have been--8:00 pace or so, rather than slightly sub-7. I'm not worried. I trust HR and perceived effort, particularly when we're talking about heavy training weeks and long runs.