Anyone, especially an alter kacker, who wants to train or just ride at a competitive or quasi-competitive level—which necessarily means some amount of high intensity work—needs a reliable physiological measure (biomarker) of stress, e.g. HRV, or the rare ability to introspect accurately and honestly about their physiological state. Because overtraining is what most of us will do and, yes, it might shorten our lives. On the other hand, so might conservative training and fast is fun.