The longest certified ultramarathon in the world is The Ultimate Ultra, the annual Sri Chinmoy 1300-Miler (2092 kilometers) which is held each fall in New York. There is also the annual Trans America Footrace, which is run in 64 consecutive daily stages from Los Angeles to New York. Runners cover almost 3,000 miles (more than 4800 kilometers) at a rate of about 45 miles (72 kilometers) a day.

Ultramarathons are run on roads, trails and tracks. They can be point-to-point, like the Comrades Marathon in South Africa; out and back, like the Niagara 100K in Canada; or held on loop courses, like the famous one-mile loop that Sri Chinmoy runners circle 1300 times in New York.

Rules allow runners to "go as you please." This means they may take walking breaks, pause to drink or eat and even sleep if the events are especially long, such as multi-day races. No penalty results from any such interruption, except for the time or distance a runner loses from his or her performance.

Men and women compete in ultramarathons at all levels. They always have. In modern times, they usually compete together in the same race. One hundred years ago, when the sport flourished as "pedestrianism," men and women competed in separate events.

There are two types of events - those in which runners set out to cover a fixed distance (whether it be 100 kilometers, 1000 kilometers or more) and those in which runners attempt to cover the greatest possible distance within a fixed period of time (such as 24 hours, 48 hours or six days).

Journey running is another aspect of the sport. Journey runners are lone trekkers who set out to cover long distances at their own daily pace. The most common examples are transcontinental runners, such as those who have crossed Canada, the United States and Australia on foot, or those who have run from John O'Groats to Land's End in Britain.

Megarunners are another sub-group within the sport. They are known not for their speed or records but for the great number of marathons and ultramarathons they run. Henri Girault of Naintre, France, has run more than 200 races of 100 kilometers or more. American Norm Frank of Rochester, New York, has run more than 550 marathons and ultras. And Canadian Wally Herman of Ottawa has run more than 400 such races, including at least one marathon or ultra in every Canadian province and territory, every U.S. state and in more than 70 countries worldwide.

There are Standard and Non-Standard ultramarathon events, although ultrarunners do not always agree which events fit in each category. The most generally accepted Standard events are 50 Kilometers, 50 Miles, 100 Kilometers, 150 Kilometers, 100 Miles, 24 Hours, 200 Kilometers, 48 Hours, 200 Miles, Six Days, 1000 Kilometers and 1,000 Miles.

Six Days became a major Standard racing distance in the last century, when ultramarathoning was known as pedestrianism. It was the longest event that could be held without competing on Sunday. Typically, six day races started at the stoke of midnight on Sunday night and concluded at the same time the following Saturday night. Non-standard "events" include all other measures of time and distance, and they can be numerous and demanding for statisticians to monitor.

During the course of one long race, for example, runners may be timed or measured through many "splits," or intervals, and can sometimes set numerous records in the process. In a six-day race, athletes pass through literally dozens of race intervals, Standard and Non-Standard.

The categories multiply even more when Metric and Imperial distances are taken into account.

Ultramarathon racing is much older than the marathon (which originated with the first modern Olympics in 1896) but only recently has the sport has been recognized by the International Amateur Athletic Federation (IAAF). In 1991, the IAAF extended official recognition to the 100-kilometer event. Since that time the 100-kilometer event has replaced the marathon as the longest running distance recognized by the world athletics governing body. The annual IAU 100-Kilometer World Challenge is now held each year by the International Association of Ultrarunners "under the patronage of" the IAAF.