Hi John,
How about daily cycles -morning to night?
This video mentions tap testing - also things like a heart rate variability ring that will tell you if you are in sympathetic or parasympathetic dominance ..also mentions that we can improve our BBB integrity with hot/cold alternating showers...ways to finesse the edges and get a read on tolerances .
24 Ways To Hack Your Biological Age From Ancient Wisdom & Modern Science | Ben Greenfield - YouTube
Kind regards,
md