I can't remember the name of it, but when I was in undergrad over a decade ago the new fad was a whole trademarked system one could purchase that attemped at quantify stress and fatigue (based on heart rate and some other physiological values), plan programming based on that and prevent overtraining. It was computer based and of course it cost an arm and a leg and didn't work. Do you remember it Jordan?
Then HRV came around, and from what I understand it also didn't do much to accomplish this either.