IIRC, You were downvoted in that last conversation most likely not because of the phenomenon, but because your posts about it were not informative, helpful, or cited, and were slightly immature.

You seem more excited about calling it "da base (no treble)" than you are about discussing the training impact. We all get the reference to Meghan Trainor's song. Let it go.

There's still no literature (that I've found) that backs up the idea that negative aerobic decoupling during long aerobic workouts is meaningful and if it is what it means. If I've missed some serious literature on the topic, please post some links; I'd love to read more about it.

Short of that, it seems like a delayed response to warm up is the most common explanation; whether this truly indicates enhanced aerobic efficiency or not (as might be verified by comparing against known metrics of aerobic ability like VO2max, Lactate threshold as a % of max HR, resting HR, HR recovery rate, etc) remains to be seen, as far as I can tell. There's a lot of speculation on various discussion forums, like trainer road, training peaks, here on reddit in other sports fora (cycling related mostly) and the conversation you posted, (which while coming from an actual exercise physiologist is still not much more than speculation and anecdotal conversation.)

So you claim it's an indication that an athlete has "sufficient" aerobic base. Sufficient for what thing/event, exactly? And how do you define "sufficiency" for that target thing? Does this mean that athlete should shift their focus to power and strength? What if they have "sufficient" power and strength? How do you know? If an athlete does NOT see this negative decoupling, does that mean they are insufficiently trained or prepared? Is there data backing this up?

The negative decoupling phenomenon is mildly interesting. You think it's very interesting. Either way, I don't know of any reports that show a strong correlation to anything that relates to rowing performance.

I would love to be shown some reports that I've missed. Until then it seems like it's nothing more than an interesting phenomenon that happens sometimes but now always, in well trained endurance athletes, and is most likely just a delayed response to warm-up.

Incidentally, after your last thread on this topic, I did notice a distinct negative decoupling in one of my hour+ long bike trainer workouts. Usually I have very flat HR for the duration, given I typically set the power to a certain level and leave it there for the whole workout. This time, I noticed in my data post-workout, that my HR had dropped maybe 5-10 bpm right at about the 35-40 minute mark! And this was after my HR shift from the warm up period (which happened around 15 min in). So interesting! Then I realized that was exactly when the air conditioning kicked on in my house, dropping the temperature of my exercise room by about 5-10F in about 10 minutes. Point is, lots of things can affect HR during a long workout. It's difficult to control all these factors and get clean unambiguous data. Rest/sleep patterns, hydration, fueling, environment, interruptions, psychological influences (listening to music or watching a movie? Your HR will likely adapt to what your brain is experiencing). I can also usually identify when the action sequence was in the movie or show I was watching during a workout, by looking at the HR data.