I haven't done anything over the top. Swimming distance is always hard for me, and soccer midfield is tough in a fast paced game.
Most difficult? One 10k I ran was accompanied by some intense humidity. It was like suffocating in my own skin while running. Not a good combo.
ENFP Male: E-74% N-95% F-58% P-84% 3w2
"I feel there are two people inside me - me and my intuition. If I go against her, she'll screw me every time, and if I follow her, we get along quite nicely." -Kim Basinger
My uncle whos a fitness guru got me on a "road work" exercise program, which is what the UFC fighters use. Its a combination of ballistic weight training rounds broken up with 10 min sprints. I passed out after round 2 sprint the first time.
Also, pointe work in ballet is the definition of pain.