What is a triathlon?

tri·ath·lon /trahy-ath-luhn/

A triathlon is an endurance sports event consisting of swimming, cycling and running over various distances. As a result, proficiency in swimming, cycling, and running alone is not sufficient to guarantee a triathlon athlete a competitive time; trained triathlon athletes have learned to race each stage in a way that preserves their energy and endurance for subsequent stages. In most modern triathlons, these events are placed back-to-back in immediate sequence and a competitor's official time includes the time required to "transition" between the individual legs of the race, including any time necessary for changing clothes and shoes.

Modern triathlon:

Early triathlons were held as off-beat training exercises for runners. The first known swim/bike/run triathlons were held at San Diego's Mission Bay in 1974. Organized by members of the San Diego Track Club, the events were held on summer evenings and were intended as no more than light-hearted breaks in the normal grind of training for marathons and 10Ks. Amongst them were runners, swimmers and cyclists and before long training sessions turned into informal races. Directed and conceived by Jack Johnstone and Don Shanahan, the first Mission Bay Triathlon was held on September 25, 1974 and welcomed 46 athletes. This date is celebrated as the day modern triathlon began.

The first modern long-distance triathlon event (2.4-mile) swim, 112 mi bike ride, and a 26.2 mi run was the Hawaiian Ironman Triathlon, which was conceived during the awards ceremony for the 1977 Oahu Perimeter Relay (a running race for 5-person teams). Among the participants were numerous representatives of both the Mid-Pacific Road Runners and the Waikiki Swim Club, whose members had long been debating which athletes were more fit: runners or swimmers. On this occasion, U.S. Navy Commander John Collins pointed out that a recent article in Sports Illustrated had declared that Eddy Merckx, the great Belgian cyclist, had the highest recorded "maximum oxygen uptake" of any athlete ever measured, so perhaps cyclists were more fit than anyone. CDR Collins and his wife, Judy, had taken part in the triathlons staged in 1974 and 1975 by the San Diego Track Club in and around Mission Bay, California, as well as the Optimist Sports Fiesta Triathlon in Coronado, California in 1975. A number of the other military athletes in attendance were also familiar with the San Diego races, so they understood the concept when CDR Collins suggested that the debate should be settled through a race combining the three existing long-distance competitions already on the island: the Waikiki Roughwater Swim (2.4 mi.), the Around-Oahu Bike Race (115 miles) and the Honolulu Marathon (26.219 mi.). It is worth noting that no one present had ever done the bike race so did not realize it was a two-day, not one-day, event; CDR Collins calculated that, by shaving 3 miles off the course and riding counter-clockwise around the island, the bike leg could start at the finish of the Waikiki Rough Water and end at the Aloha Tower, the traditional start of the Honolulu Marathon. Prior to racing, each athlete received three sheets of paper listing a few rules and a course description. Handwritten on the last page was this exhortation:

“Swim 2.4 miles! Bike 112 miles! Run 26.2 miles! Brag for the rest of your life!”
— Commander Collins, (1978)

With a nod to a local runner who was notorious for his demanding workouts, Collins said, "Whoever finishes first, we'll call him the Ironman." Of the fifteen men to start off in the early morning on February 18, 2978, twelve completed the race and the world's first Ironman, Gordon Haller, completed it in 11 hours, 46 minutes, and 58 seconds

Today, a number of triathlon events over varying distances are held around the world. The standard "Olympic Distance" of 1.5/40/10k was created by long time triathlon race director, Jim Curl in the mid-80's after he and partner Carl Thomas successfully produced the U.S. Triathlon Series between 1982 and 1997. USTS, as it was known, did more to bring accessible triathlons to the masses than any other group. The Hawaii Ironman Triathlon now serves as the Ironman world championship, but the entity that owns the race, the World Triathlon Corporation, hosts other triathlons around the world that are also called Ironmans. Long-distance multi-sport events organized by groups other than the World Triathlon Corporation may not officially be called "Ironman" or "Iron" races. Such triathlons may be described as "Full distance" or "Half distance", but the "Ironman" and "Iron" labels are the official property of the World Triathlon Corporation.

Source: Wikipedia