Good question.

First, one quick correction: the upper limit of nose breathing would be the top of Zone 2 rather than Zone 1.

Second, if your breathing doesn’t feel noisy and labored, then I think it’s safe to say that you’re below your aerobic threshold. (The top of Zone 2 is marked by the aerobic threshold.) In that case, you could continue at that intensity or increase your pace until your breathing becomes noisy and labored.

Third, it’s not necessary to train right at your aerobic threshold all of the time. The “noisy and labored” quality is just a good benchmark to feel when you’re there.

Fourth, it is possible to nose breathe above your aerobic threshold, but usually, it happens if you haven’t warmed up slowly enough.

I hope that helps.

Thanks for bringing that up. That could definitely be the case.

I’ll ask Scott J. to weigh in and clarify.

Thanks Frantik for digging up that old forum post

debougknecht 1
While this is a misprint in the book and I am embarrassed by it (we’ll have to wait till the net printing of the book to correct it) it’s not really important what you call the upper end of the basic aerobic zone, either zone 1 or 2. What is important is that ventilation markers like nose breathing or conversational pace can be good markers of the aerobic threshold. If you can maintain a conversation or breath through your nose, chances are decent that you are in an aerobic metabolic state. This is not a 100% fool proof method, especially when one has a history of lots of high intensity training (I can’t tell you why). What is the HR you are maintaining for this 2 hour workout? How old are you? Can you get up the next morning and repeat it at the same pace? And then do this again the next day and the nest and the next? Then you are below your aerobic threshold. If you are too tired to repeat it the next then it was too high of an intensity the first day.

I hope this help.
Scott