An ultramarathon, also known as ultra distance or ultra running, is any footrace longer than the traditional marathon length of 42.195 kilometers (26 miles 385 yards) . Various distances, surfaces, and formats are raced competitively, ranging from the shortest common ultramarathon of 31 miles (50 km) to the worlds longest certified footrace, the Self-Transcendence 3100 Mile Race. Ultramarathons can be run on roads, trails, mountains, snow, and other terrains. The largest ultramarathons are on the road, including the Comrades Marathon and Two Oceans Marathon. Ultramarathons can be run as single loops, point-to-point road or trail races, or cross-country rogaines. Many ultramarathons have significant obstacles, such as inclement weather, elevation change, or rugged terrain. Aid stations are usually available during ultramarathons, which are supply checkpoints during the route that supply runners with food and hydration, and there are usually medical personnel there just in case. People run ultramarathons for various reasons, including personal fulfillment, making friends, and getting out and about. To train for an ultramarathon, a combination of running, cross-training, strength training, and rest days is recommended, and it is important to train on terrain similar to what you will experience in the ultramarathon.