USATF is a governing body over many road, trail and ultra races in the US. Personally I’m not a big fan of too many sanctions on sporting events, especially when road sanctions get applied to trail events (can we say no headphones policy?). The USATF has a recently added category called "MUT" which stands for Mountain/Ultra/Trail. But what’s the difference? See below:
Any running race with extreme amounts of climbing or climbing and descending – generally more than 300’ per mile. While most mountain races are held on trails, there are many – generally hill climbs – held on steep mountain roads. The oldest and most prestigious of which is the Mt. Washington Road Race in Pinkham Notch, New Hampshire. First held in 1936, this classic mountain race climbs 4200’ in 7.6 miles (www.mountwashingtonroadrace.com). While mountain races can be any distance, the World Mountain Running Championships are generally 9k in length for women and 12k for men.
Races longer than a marathon (26.2 miles) are considered ultra-marathons, or “ultras”. Ultra races can be any length over 26.2 miles, but many have been standardized at 50k, 50 miles, 100k, 100 miles or 24 hours. Ultra races are held on both on and off road as well as on flat, hilly or even mountainous terrain. One of the most famous ultra races is the Western States Endurance Run (100 miles) held in the Serria Nevada mountains of California (www.ws100.com).
As the name suggests, “trail running” races are held off-road. There are many long trail races that could also be considered ultra races. Likewise, there are many very hilly trail races that could be considered mountain races. While there is no specific world championship in trail running, this sport is growing in popularity and is enjoyed by both elite runners and the occasional “jogger”.