I never really thought of it as "suffering." Except for lethal wounds, there really isn't anything I can't endure (it's the mantra of the Rational-Emotive School of psychology -- "Will it kill me? No? Then I can hang on even if the only reward is the gift of survival."). The Columbia Sportswear parka commercials call it "endurance testing." It's a challenge. Like when I go into Sweet Melissa, a pastry shop and trufflery near me, and order the lunch-sized green salad with the cherry-balsamic vinaigrette and have green tea for dessert. It's a personal Everest, and there's a greater climax/plateau up there if you're willing to deal with some "workout pains."
Edit: I love this forum. Being in extremis in any way is the only way to get to know yourself. We are the Sex Warriors, more Aurelius than Kinsey, more Aeneas than Troilus, more diva than chorine...