Mountain bike racing (shortened MTB or ATB racing) is a competitive cycle sport held on off-road terrain. The Union Cycliste Internationale (UCI) recognised the discipline relatively late in 1990, when it sanctioned the world championships in Durango, Colorado. The first UCI Mountain Bike World Cup series took place in 1991. Its nine-race circuit covered two continents—Europe and North America—and was sponsored by Grundig. Cross-country racing was the only World Cup sport at this time. In 1993, a six-event downhill World Cup was introduced. In 1996, cross-country mountain biking events were added to the Olympic Games. In 2006, cross-country mountain biking events became part of the World Deaf Cycling Championships for the first time in San Francisco, USA.