its debut at the summer Olympic games in Atlanta. Given the enormous variation of terrain a mountain bike can navigate, a division took place as a cause of riders' specialisation. Types Cross-country – Cross-country (XC) racing is held on a varied terrain circuit, it is normally around 6–8 kilometers (km) and is always a massed-start race. Under the 2006 UCI rules, elite, U23, and Junior Expert riders at UCI sanctioned races, are allowed technical assistance, but only in designated zones and only by an authorized team mechanic. However, riders in the same team can help each other at any point in the race. Under NORBA rules, no technical assistance is allowed. Professional level races are longer in distance, around 50 km. Cross-country olympic (XCO) Short Track Cross-Country – Short track cross country (STXC) is a very short XC style event of about 800 m in length but generally about 1 minute 30 seconds in winning time. A short, sharp exciting event to watch and participate in. Also called Cross-country eliminator Downhill – Downhill (DH) racing is a time trial event. Riders start at intervals that can vary from 30 seconds to three minutes-depending on the stage of the competition – and the rider with the lowest time wins. As the name of this discipline implies, DH races are held in steep, downhill terrain, resulting in higher speed than in cross-country racing. The terrain is also significantly rougher than in cross-country racing. The bike is designed with long travel suspension and hydraulic disc brakes. Super D – Super D (SD) is a blend of cross-country and downhill. Most of the race is downhill, on trails similar to the downhill segment of a cross-country race. There are also short (100–500m) uphill sections which make the use of downhill bicycles difficult, as a result, most riders use cross-country or 'trail bikes'. Depending on the trail and race venue, the start may either be seeded (riders start in short intervals), or Le Mans mass start (riders run to their bikes, timing is started when the riders start running). Probably the most famous of this type is the Megavalanche. Freeride – Freeride (FR) competitions are not so much a race as they are a competition of skill and style. Courses contain varying cliffs, drops, obstacles, and ramps. There are usually a large number of ways in which to complete the course, and scoring is dependent