What is the Todd Davenport approach to pacing?

I just listened to a very interesting interview with Todd Davenport ( Pacing and how to exercise safely in Long Covid and ME/CFS ) in which he discusses using heart rate and heart rate variability to guide patients in how to stay below their PEM threshold. He said lots of interesting things - obviously, there's a lot to this topic - and rather than guddle about all over the Internet trying to…