[Jack Kuenzle]

Those ventilatory indictors (nose breathing, ability to hold a conversation) are just not very effective for estimating LT1/AeT. They tend to be quite conservative. Nose breathing stops for me around 125, I can’t hold a conversation very fluidly above 140, but my AeT is 155. I see this with many athletes. For some, those ventilatory indicators are quite accurate, for others not so much. No reason to be concerned.

 

So the aerobic system responds quite well to high frequency stimuli. Better to more, smaller stimuli than fewer, longer stimuli. Yes there are many practical reasons to do longer runs (building fatigue resistance, training carb ingestion, improving fat adaptation….), but this is why you see elite road runners doing doubles and triples instead of consolidating all their daily mileage in a single run. For an athlete like you who doesn’t currently have a specific objective coming up, frequent shorter runs is honestly better.

 

As far as how hard to do these runs, it’s hard to say. It comes down to how aerobically fit you are, your ability to recover and handle training stress, and the amount of time you can allocate for training. An aerobically untrained athlete could do all of their volume quite close to AeT and be fine. For an aerobically fit athlete training in Zone 2 can be extremely taxing. Training closer to AeT will always be better quality stimulus second to second, but it’s way more stressful, especially for aerobically fitter athletes. Complicating this further, factors like heat and dehydration and recovery can really drive up heart rate and a run that’s quite easy RPE wise could be drive into Zone 2. I’d remember that Zone 2 is not training at AeT, but training in a zone that extends 10% below AeT (Assuming 172: 155-172).

 

Reading your comment, it sounds like you are constrained by time and not by recovery. If you had more time, you’d assign more stress to your training plan. By that, I would train in Zone 2 for most of my work. If I found I was having trouble recovering in between runs, I’d drop the training intensity. Heart rate is not a terribly precise way to assign intensity so I wouldn’t get too wrapped around whether activities are in Zone 1 or Zone 2. I’d use AeT as an absolute ceiling for base work, but guide day to day intensity based on perceived exertion. When you are eventually able to increase training time, I would decrease training intensity so you have the capacity to increase volume.

 

Let me know if you have any further questions.