Ultramarathons are quickly becoming this generation’s marathon: everyone seems to be doing an ultra-distance race! Anna Mae Flynn running in the Grand Canyon. PC Joshua Stevens The sport of ultra running is exploding right now. Consider that the number of ultramarathons grew by about 1,000% over the last decade. In 2006, about 160 races were listed around the world. Last year, that number grew to an incredible 1,800. In 2003, nearly 18,000 people finished an ultra in North America. That…