The Ironman series — triathlons with a 2.4-mile swim, 112-mile bike and 26.2-mile run — is widely considered the ultimate test for endurance athletes.

Shorter versions all over the world attract both serious athletes competing for prize money and weekend warriors who want to experience a slightly less painful version of the Ironman fantasy.

Although interest in traditional triathlons remains high, many athletes are turning their attention to another form of long distance competition: off-road endurance racing. 

Xterra off-road triathlons are the most well-known of these events because of cable TV coverage and corporate sponsorship. Yet much of this sport's growth takes place away from the spotlight.

Sweden's Otillo Race is not a triathlon, but it ups the adventure quotient. During the event, competitors travel in pairs between the Swedish islands of Uto to Sandhamn. They swim a total of 6.2 miles, but they don’t stay in the water continuously. There are 26 islands along the course, and racers get out of the water at each land mass and run across it. The total distance of the running sections is 40.4 miles.

Otillo has no transition stations where athletes can change out of their wetsuits and stock up on water and energy bars. Many competitors simply run in their wetsuits and swim in their sneakers.

Otillo is a great example of the ways in which the off-road endurance niche is developing. The attractiveness of these events is based as much on adventure and human vs. nature challenge as it is on crossing the finish line first.

Marathon des Sables in Morocco

Runners take on the 156-mile Marathon des Sables in Morocco. (Photo: tent86/flickr)

The proof of off-road racing's popularity growth is in the numbers. Otillo has a limit of 240 racers. More than 1,000 people had to be turned away during registration for the most recent race.

Otillo's growth mirrors that of the Xterra off-road triathlon series. Xterra, first sponsored by the Nissan all-terrain vehicle of the same name, began in 1996 as one race run by several dozen competitors. Today, Xterra holds more than 300 events all over the world. About 60,000 people took part last year.    

Traditional endurance athletes (road triathletes) take part in these off-road races, but specialists usually have the most success. Quickly negotiating steep terrain on mountain bikes and foot requires technical skills. And though many races have well-marked trails, others require navigational skills and have checkpoints that competitors must find along the route.

Xterra races are shorter than Ironman triathlons. Most consist of 1-mile swims, 20-mile mountain bike rides and 6-mile trail runs. The relatively short distances make these events attractive to amateurs as well as pros.   

The trend of bringing racing back to nature goes beyond triathlons. The Adventure Racing World Series holds multi-day events contested by teams of racers. These expedition-style competitions feature trail running, mountain biking and sometimes swimming. Teams also must have skills in kayaking, mountain climbing, navigation (usually without a GPS) and camping.

The U.S. Adventure Racing Association holds a variety of events throughout the year. Unlike the AR World Series, these generally do not require corporate sponsorship, though participants must win qualifying rounds to take part in top-level races.

Xterra race in Waiuku

Contestants compete in an Xterra race in Waiuku, New Zealand. (Photo: Robert Engberg/flickr)

Endurance purists like to make the racing equation as simple as possible by removing all equipment except a good pair of running shoes. For these people, off-road ultramarathons are the ultimate test of human endurance.

The Marathon des Sables (also known as the Sahara Marathon) is a 156-mile run that passes through one of the world's most inhospitable regions, the Sahara Desert in Morocco. Widely considered the Earth's most challenging footrace, Sables has been dominated by Morocco's Ahansal brothers, who have won more than half the events since the race first took place in 1986.

Other challenging ultramarathons have become so popular that they have spawned entire series. The Ultra-Trail du Mont-Blanc is a 100-mile race that requires runners to ascend nearly 10,000 feet. Its success inspired a series of ultra events that draw 10,000 runners to the Alps of France, Italy and Switzerland each year.

In the U.S., the 100-mile Western States Endurance Run — started in 1977 — carries one of the top long-distance prizes. Competitors must climb a total of 18,000 feet and descend nearly 23,000 feet. They must deal with snow at higher elevations and sweltering heat in the valleys. The course record is an astonishing 14 hours, though anyone who completes the run in less than 30 hours gets an award.

Perhaps part of the allure of off-road racing and outdoor adventure sports is that they are so different from what most people experience during day-to-day life in the computer-driven modern world. The elements of outdoor skill make these events more about adventure and experience, whereas traditional triathlons are simply about enduring the pain long enough to cross the finish line. 

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