There are different types of starts for races of different distances. Middle- and long-distance races mainly use the waterfall start. This is when all athletes begin on a curved line that moves farther out at the outer edge of the track. Competitors are allowed to move towards the inside lane right away, as long as it is safe to do so. For some middle-distance races, such as 800 m, each athlete starts in their own lane. Once the gun fires, they must run in the lane they began in until markers on the track notify them it is time to move towards the inside lane. For sprint races, athletes begin in start blocks and must stay in their own lane for the entire race.