hmm...I understand how from a learning theory perspective one would habituate and become desensitized to the anxiety provoking stimulus. It's the old saying that the only way to conquer fear is to face it. OK.
But You say there is only a finite production of adrenaline/epinephrine....
Do multiple jumps produce adrenal fatigue then? How does the body not experience jumping as a chronic stressor if you do it regularly? What about cortisol, chronic sympathetic arousal etc...?
I'll check out Grey