That is interesting because it suggests that maybe the problem has nothing to do with use of energy in muscles but is to do with what is happening to the heart. Perhaps PEM is all to do with autonomic nervous system signalling in relation to heart activity.
One of my first symptoms was strong palpitations after trying to exercise. My fitness at the time was very good so something definitely changed in a short amount of time.
Do you think the autonomic nervous system "sensitized" into sending PEM signals when the heart is being used. Or is the autonomic nervous system sending incorrect signals to the heart which then causes further issues that produce PEM? Also if the autonomic system is having signaling problems, is it possible that what is happening to the heart is caused by signaling in relation to vascular contraction/dilation?
I think Systroms work is pretty convincing in showing an abnormality. What role that plays in producing PEM and what the cause of the abnormality is, I think it very much in question.