Runners take on China's 'most-testing' marathon

Main sponsor Abbott Labs offers essential medical backup for Great Wall challenge

Long-distance running has become big business in China - a fact not lost on Abbott Laboratories, the United States healthcare company, which was one of the main sponsors of this year's 16th Huangyaguan Great Wall Marathon, held on Saturday in Tianjin.

According to the organizers, around 2,500 people from 50 nations and regions took part in the event.