Long-time runner here. One of the symptoms that clued me in to an autonomic issue was my heart rate progressively stopped keeping pace with my workload, over the course of a year.
The experience was different than simply being tired from a maximum effort (burning lungs and burning/aching limbs). It was this feeling like my heartbeat and breathing were not keeping up with my legs. My HR monitor backed up this story, showing a 10-15 bpm decline during max efforts.
I've had cardio workups, nothing structurally wrong with my heart, though I do have prolonged QT.
Googling around I found the term "chronotropic incompetence" - here's an overview: https://www.ahajournals.org/doi/full/10.1161/CIRCULATIONAHA.110.940577
Athletes, have you experienced this? Were you able to do anything about it?
Thanks 🙏