I'm obsessed with the idea that our mind is as powerful or even more powerful than our body.  With all my experiences in ultra-endurance mountain biking, I've seen over and over that mental toughness really plays a roll in how hard you can push yourself and what you believe you are capable of. I was thrilled to find the book: Endure: Mind, Body, and the Curiously Elastic Limits of Human Performance by Alex Hutchinson.  It was jam packed with really interesting research on whether limits live in our mind or our body. I also looked up Alex and learned that he is a National Magazine Award-winning journalist whose work appears in Outside, The New York Times, The New Yorker, and more.  Another fun thing I learned was that he is a very accomplished runner, running on the Canadian National Team and even more interesting, he is actually Dr. Alex Hutchinson - he has his PhD in Physics.  Getting a PhD in Physics would be the true test for pain tolerance!  I did my Master's in Electrical Engineering which is basically all Applied Physics and it is really something else. I can't imagine doing the full monty and getting a PhD in Physics!