An ultramarathon, also called ultra distance, is any sporting event involving running and walking longer than the traditional marathon length of . There are two types of ultramarathon events: those that cover a specified distance, and events that take place during specified time (with the winner covering the most distance in that time). The most common distances are , , , and , although many races have other distances. The 100 kilometers is recognized as an official world record event by the International Association of Athletics Federations (IAAF), the world governing body of track and field. Other distances/times include double marathons, 24-hour races, and multiday races of or even longer. The format of these events and the courses vary, ranging from single or multiple loops (some as short as a track), to point-to-point road or trail races, to cross-country rogaines. Many ultramarathons, especially trail challenges, have severe course obstacles, such as inclement weather, elevation change, or rugged terrain. Many of these races are run on dirt roads or mountain paths, though some are run on paved roads as well. Usually, there are aid stations every apart, where runners can replenish food and drink supplies or take a short break. Timed events range from 6, 12, and 24 hours to 3, 6, and 10 days (known as multi-day events). Timed events are generally run on a track or a short road course, often one mile (1.6 km) or less. The International Association of Ultrarunners (IAU) organises the World Championships for various ultramarathon distances, including , , 24 hours, and ultra trail running, which are also recognized by the IAAF. Many countries around the world have their own ultrarunning organizations, often the national athletics federation of that country, or are sanctioned by such national athletics organizations. World records for distances, times, and ages are tracked by the IAU.