Welcome to the forum.
I am assuming you did an indoor or outdoor AeT test last year and another one recently. You mentioned that pace has dropped on trails, did you see a drop in your AeT based on the tests?
So, I started with TFTNA almost exactly a year ago. When I began this training, I could run a 10k in ~50 minutes, but I had no “conversational” pace. If I was moving, I was panting. I had all the classic symptoms of aerobic deficiency syndrome, so I threw myself into long, slow jogs/runs. At first, I could only job downhill; I had to mostly walk to keep my HR below AeT. I was doing 15-16min miles. By summer, I was down to 12 minutes. Great! My AeT even nudged up a few beats. But come fall, I was slowing back down again. I tried taking two weeks off, but when I returned, the problem persisted. I’ve tried lowering my training volume. I’m even seeing an allergist to be treated for possible exercise-induced asthma with Montelukast and Symbicort with an inhalation chamber (my spirometry came back negative for asthma, but I have all the symptoms, so my doc agreed to let me try treatment). Nothing has helped. I’m right back to where I was a year ago, having to jog my downhills, jog/walk flats, and take many pauses on uphills to stay below AeT.
I live in Seattle, and our winters are very mild. It’s not like I’m trying to perform in sub-freezing temperatures.
I don’t have any history of illness. I saw a cardiologist a few years ago due to high heart rate during exercise (I was a college rower and I’d regularly hit 210bpm on my workouts), but he found no problems. His answer to me was “some people just have higher heart rates.”
I’m super frustrated and unsure of where to turn next. Has anyone dealt with regression in their aerobic conditioning?