

Now there are concerns that in China and beyond, a proliferation of new races has created a risk that safety rules will not always be enforced, and with it a chance that some of the most obsessive participants will discard vital protective equipment in the interests of gaining an advantage over their rivals. But ultrarunning has boomed in popularity in recent years, with the number of finishers around the world rising from 120,000 to more than 600,000 in a decade. To most people, the horror of 21 lives being lost during a race across 100km in a Chinese mountain range will have been amplified by how obscure the sport seems to outsiders.
