A truly punishing test of human endurance, triathlon pushes its competitors to the limits in three different sports: swimming, cycling and running.
Each sport requires competitors at the top to be in peak physical condition - just reading a triathlete's training schedule would exhaust many people - but triathlon is still accessible to all ages and abilities.
Why is it good for you?
Triathlon involves high-intensity activity for a prolonged period of time. This improves cardiovascular fitness, builds stamina, lowers blood pressure and helps prevent heart disease.
A triathlon race is incredibly physically demanding and one held using Olympic distances burns approximately 2,750 calories. Training for all three categories will also aid the loss of body fat.
The triathlon works all the muscle groups in the body in a variety of ways. Running helps develop lean muscles, swimming boosts the upper body and cycling tones your lower body.
As triathlon has three disciplines, the range of different exercises helps prevent repetitive stress injuries which can occur when focusing on one event, such as joint problems, shoulder problems, tendonitis, fractures or shin-splints.
For people of all ages and abilities wanting to take part, there are approximately 750 triathlon clubs in the United Kingdom. Many clubs offer taster sessions for people interested in taking up the sport.
Club membership entitles you to easy access to coaching and entrance to races. Coaches can also advise you on essential kit and may be able to help you out with second-hand gear.
Information on how you can join can be found on the
Non-professional athletes take part in the age-group system, where you compete against athletes of the same age (within a five-year band) and sex. Elite athletes compete at an international level.
You do not need a purpose-built tri-suit to compete but something close-fitting and comfortable and, if you are taking part in an open-water swim, that can be worn under a wetsuit, is recommended.
Some clubs offer use of wetsuits for hire, or occasionally for free. Owning your own goggles is advised.
Unless you are racing at an elite level, you do not need to worry about the quality of your bike. You will need your own helmet, however.
No specific equipment is required for the run, although good-quality running shoes are advised.
More on the British Triathlon website
Triathlon is a relatively new sport and its origins are unclear, with some saying it began in France between the First and Second World Wars.
The first official triathlon was organised in 1974 in Mission Bay by the San Diego Track Club as an alternative workout to track training.
Did you know?
Alistair Brownlee became Britain's first Olympic triathlon champion at London 2012, with younger brother Jonny taking the bronze medal.
Triathlon arrived in Britain in 1983, with the British Triathlon Association founded the same year.
The International Triathlon Federation (ITU) was founded in May 1989 and the first World Championships took place in the same year in Avignon, France.
In 1991, the ITU launched its first full season of the World Cup circuit, and triathlon made its Olympic debut at the 2000 Sydney Games.
More on the IOC website