Cycle sports are held on tracks, roads, and cross-country circuits. Races range from 1,000 meters (1094-yd) sprints on an indoor track to multi-stage events over hundreds of kilometers that last a week or more. Special courses are prepared for off road racing, which includes cyclo-cross and mountain-bike racing. Fun and environmentally friendly, the bicycle is the simplest form of mechanical transport. Cycling is very popular around the world. It is a great way to keep fit, as well as a cheap and non polluting means of transport. “Mountains bikes”, first designed for off road cycling, which are now common in cities too. In recent years, professional bicycle racing has been marred by revelations of the use of performance-enhancing drugs. Several favorites were barred from the 2006. Bicycling for off-road races has chunky tyres for the rough terrain. In many countries most people travel or transport goods by bicycle. Across the world, cycling and motorcycles are used for sports and leisure.