A triathlon is an endurance sports event consisting of swimming, cycling and running over various distances. As a result, proficiency in swimming, cycling, or running alone is not sufficient to guarantee a triathlon athlete a competitive time; trained triathletes 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.
According to triathlon historian and author Scott Tinley, the origin of triathlon is anecdotally attributed to a race in France during the 1920s-1930s that was called variously "Les trois sports", "La Course des Débrouillards", and "La course des Touche à Tout". Nowadays, this race is held every year in France near Joinville-le-Pont, in Meulan and Poissy. In 1920, the French newspaper "L´Auto" reported on a competition called "Les Trois Sports" with a 3 km run, 12 km bike, and a swim across the channel Marne. Those three parts were done without any break. There are also articles in French newspapers about a race in Marseille in 1927. There is a 1934 article about "Les Trois Sports" (the three sports) in the city of La Rochelle, a race with: (1) a channel crossing (c. 200 m), (2) a bike competition (10 km) around the harbor of La Rochelle and the parc Laleu, and (3) a run (1200 m) in the stadium André-Barbeau.
Early triathlons were held as off-beat training exercises for runners. The first known swim/bike/run triathlons were held at Mission Bay, San Diego, California 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. This occurrence is well-documented and was not based on the French events. 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.
Sprint: (Swim) 750m/. 47 mi, (Bike) 20km/12.4mi, (Run) 5km/3.1mi. A 500meter swim is not uncommon for this distance.
Olympic: (Swim) 1.5k/. 93 mi, (Bike) 40km/24.8mi, (Run) 10km/6.2mi.
½ Ironman or 70.3: (Swim) 1.9km/1.2 mi, (Bike) 90km/56mi, (Run) 21.09km/13.1mi
Ironman: (Swim) 3.8km/ 2.4mi, (Bike) 180km/112mi, (Run) 42.2km/26.2mi