A 24-hour run is a form of ultramarathon, in which a competitor runs as far as they can in 24 hours. They are typically held on 1- to 2-mile loops or occasionally 400-meter tracks. Top runners will often run 200 kilometres (124 mi) or more, depending on conditions, and the best can go beyond 270 kilometres (168 mi). Some participants will have a crew to help them, but others just set up a camp with all the gear and supplies they need near the starting area to access each loop. Often 24-hour events are combined with 6-, 12-, and 48-hour events. 24-hour runs have also been held in relay formats, with runners completing a mile each in succession for 24 hours. Often these events are not internationally sanctioned, and are more for charitable purposes.