Do You Use Heart Rate Training for Ultra-Maribons?

Do you use or have your athletes use a heart rate modded? That's sort of the question of the month man. Heart rate training is just a really flawed tool for ultra-maribons. I certainly never prescribe anything by heart rate so I can't tell you the last time I've done that. It's been maybe a decade since I've said go out and run under a heart rate of 150 beats per minute or whatever it is.