Ultrarunning is the general term used to describe the activities of people who run ultramarathons. An ultramarathon is literally a distance beyond the marathon or greater than 26.2 miles. For brevity, the term ultramarathon is usually shortened to ultra.

There are two basic types of ultras, fixed distance and fixed time. Common distances for fixed distance ultras are 50K, 50 miles, 100K, and 100 miles. The most popular fixed distance runs are those in which the course is primarily trails or dirt roads.

Currently, the most common time for fixed time ultras is 24 hours.There are also some 6 and 12 hour ultras. In the United States there are also two 48 hour, one 72 hour, and one 10 day. These numbers may  vary from year to year.

Listed below are sources for additional information about the sport of Ultrarunning .