It requires the endurance of ultrarunning, the sprint speed of mountain biking, the mental toughness of open-water swimming and, at times, can put skiers in situations of real exposure.
Still, billions of people have spiritual feelings without courting great physical hardship -- and there are ways of understanding ultrarunning that don't depend on spirituality.
True's inclusion in the book garnered him some attention in ultrarunning circles, and some readers credited him as their inspiration for taking up the sport.
Many countries around the world have their own ultrarunning organizations, often the national athletics federation of that country, or are sanctioned by such national athletics organizations.