The ES Endurance Association

Endurance is one of the most demanding equine sports, both for the rider & for the horse.
Rides are divided into 'Legs' of various distances. The completion of each individual leg sees the horse being checked over by a Vet. At each 'Vet Check', the horses' vital signs are checked for abnormalities. Heart Rate and Pulse, Respiratory, Gut Sounds, Hydration & Capillary Refill are the usual vitals tested. If the horse fails to show all these as normal, the horse is no longer allowed to compete in the race-the horse is 'Vetted Out'. Horses travel at an average speed of 14-20km per hour, dependant upon the skill and level of the athlete.
Horses are usually distinguished by the number of kilometres they have covered successfully (rides with no Vet-Outs). The most Elite in the Sport compete in Marathon Events that can cover up to 400km over a period of days.

"You don't have to ride an Arabian to succeed in Endurance, but you will have to pass one to win."

Arabians and their derivatives are reknowned as the most successful in the sport. Their greatest Endurance asset is due to their high percentage of slow-twitch muscle fibres, or in other words, their aerobic capacity, they are able to supply oxygen to their muscles more rapidly than, say, Quarter Horses, who have a high percentage of fast-twitch/anaerobic muscle fibres-which give them their sprinting ability.
Arabians also possess quite a few more genetic traits that contribute to their Endurance suitability, & most of these are inherited through offspring. Lung capacity, leg structure & hoof structure have also been shown to differ slightly to breeds that have had more human intervention during their evolution. Arabian horses are a product of the desert, thus their recovery times after strenuous exercise & their ability to hold water reserves are also of great benefit.

Owners of other breeds have no need to run out and buy themselves as Arabian Horse to compete in Endurance though. All of the above stated aspects that are the foundation of a well bred Endurance horse are able to be recruited into any breed, by training & routine in the individual, & selective breeding by attribute. Some of the most successful of Endurance Horses have been of the Appaloosa & Thoroughbred Breeds. So don't be discouraged. If your horse has the will to succeed & you have the seat to endure the long hours in the saddle, this sport is for you :-)

It takes, on average, a training period of 2-3 years to bring a horse to the point where they are ready to begin competing, & will continue to compete successfully well into their teens with no major physical or mental mishaps.