A triathlon is a multiple-stage competition involving the completion of three continuous and sequential endurance disciplines. While many variations of the sport exist, triathlon, in its most popular form, involves swimming, cycling, and running in immediate succession over various distances. Triathletes compete for fastest overall course completion time, including timed "transitions" between the individual swim, bike, and run components. The word "triathlon" is of Greek origin from τρεις or trei (three) and αθλος or athlos (contest).
Triathlon races vary in distance. According to the International Triathlon Union, and USA Triathlon, the main international race distances are Sprint Distance, which has a 750 metres (0.47 mi) swim, 20 kilometres (12 mi) cycling, 5 kilometres (3.1 mi) run; Intermediate (or Standard) distance, commonly referred to as "Olympic distance" (1.5 kilometres (0.93 mi) swim, 40 kilometres (25 mi) bike, 10 kilometres (6.2 mi) run; the Long Course (1.2 miles (1.9 km) swim, 56 miles (90 km) ride, 13.1 miles (21.1 km) run, such as the Half Ironman), and Ultra Distance (2.4 miles (3.9 km) swim, 112 miles (180 km) ride, and a full marathon: 26.2 miles (42.2 km) run); the most recognized branded Ultra Distance is the Ironman triathlon.
Transition areas are positioned both between the swim and bike segments (T1), and between the bike and run segments (T2) and are where the switches from swimming to cycling and cycling to running occur. These areas are used to store bicycles, performance apparel, and any other accessories needed for preparing for the next stage of the race. The time spent in T1 and T2 is included in the overall time of the race. Transitions areas can vary in size depending on the number of participants expected for the race. In addition, these areas provide a social headquarters before the race.
The nature of the sport focuses primarily on persistent and often periodized training in each of the three disciplines, as well as combination workouts and general strength conditioning.