Triathlons test competitors' abilities in three sports: swimming, running and cycling. The three races occur in a sequence, with a brief transition between races. The times of the races and the transitions add up to a total race time. Competing as a triathlete requires extensive training in all three disciplines and excellent physical and mental conditioning.
The modern sport of triathlon probably originated in France. In 1920, Joinville-le-Pont, Val-de-Marne, France was the site of a 4-km foot race, followed by a 12-km bike race, then a swim race across the Marne river. In September 1921, in Marseilles, a Course des Trois Sports was held in which both men and women raced on bicycles, on foot and swimming. The first event to call itself a trathlon - the Mission Bay Triathlon - was held in September 1974 in San Diego, California.
A triathlon may be a sprint - 750-m swim, 20-km ride and 5-km run; an Olympic or standard triathlon - 1.5-km swim, 40-km ride and 10-km run; a long course - 1.9-km swim, 90-km ride and 21.1-km run or ultra distance - 3.8-km swim, 180-km ride and 42.2-km run. The most famous ultra distance race is the Ironman competition.
To compete in a triathlon you need, at minimum, a bike, helmet and bike shoes for the cycling portion, swimsuit and goggles for the swimming segment and running shoes and shorts for the running. Some competitions require you to wear a race belt. On sunny days you may want sunglasses and sunblock. If you need socks to prevent blisters while running or biking, take those. For colder weather you may need a wetsuit to swim in cold water. For longer races, pack nutrition gels or bars and extra water. You will also want clothing to change into after the race.
Amateur triathletes compete in divisions according to age and sex. USA Triathlon, one of the governing bodies of the sport, also sanctions special divisions for larger men and women. Men who weigh more than 200 lbs. can compete in a Clydesdale division, while women who weigh more than 150 lbs. compete in an Athena division.
Information courtesy of Livestrong.com