Cardiac adaptation and more thoughts on Halfmax

Man!
Ran 8 miles yesterday evening. First 2 at 7 min pace. Heart rate max of 102. Run was supposed to be in zone 2, the bottom limit for me of which is 126 HR.

So, I picked it up to 7 min pace for the remainder 6 miles. This eventually took me into zone 2.

However, my average HR for the 42 minute 6 mile segment was 131? That is about a 6 beat drop in HR at this pace compared to 1 month ago.

My ave HR for the entire 57 minute 8 miler? 121, zone 1

My legs felt relaxed and smooth. This is a sure indication of my increasing fitness.

As for my HR correlating to power data from USAT 1/2 IM Nationals?
Ave power 301
Normal power 311 (Normal power subtracts out the coasting) I had to stop pedalling several times on the turn arounds and did coast down a few hills during the race.

The MAJOR adaptation? My ave HR for the bike segment, at over 300 watts power, was 130, zone 2.

This has got to be related to my increasing lactate threshold and VO2 max since Roth Germany in June.
Now, back in April, I raced a 46 mile TT at 301 ave Watts with a HR ave of 129. Seemingly very similar. However, that TT didnt include a pre bike 1900 meter swim, and a zone 4 HR run to transition. The pre bike swim most likely resulted in at least a 5 beat cardiac drift.

So, I believe my HR at a sustained 300 Watt effort has likely also dropped by about 5-6 beats per minute.

Now the serious push begins. 6 weeks of training to a short taper for Clearwater 70.3, then 3 weeks later IM Western Australia. Then, its a week of rest/recovery.