I was wondering if we could collate methods for guessing our anaerobic threshold without undergoing formal testing. It seems that respiration rate could be one. Ability to talk normally during exertion may be another. Heart rate (variability) is another. A combination may be the best solution. Once we have some kind of approximation, we could use a heart rate monitor to avoid going beyond the threshold. It would be such a useful thing to be able to do, to prevent PEM and consequent worsening of illness, and even facilitate improvement for some.