A truly punishing test of human endurance, triathlon pushes its competitors to the limits in three different sports: swimming, cycling and running.
Matt Chilton, BBC Sport
"The triathlon offers incredible variety as you get three sports rolled into one. Jessica Ennis gets a break in the heptathlon, but these guys do not. It is one of the few sports at the Olympics where we categorically lead the way in both the men's and the women's. Helen Jenkins and the Brownlee brothers, Alistair and Jonny, could win three of the top six medals on offer. In the women's, the main competition will come from Australian Erin Densham. Spaniard Javier Gomez has consistently threatened the Brownlee boys."
Each sport requires the competitor to be in peak physical condition - just reading a triathlete's training schedule would exhaust most normal mortals.
The six triathlon events held since the sport's Olympic debut have been won by athletes from six different countries: Canada and Switzerland in 2000; New Zealand and Austria in 2004; and Germany and Australia in 2008.
In London, 55 athletes will compete in the men's and women's events and there are no heats - it is just a one-off race to determine the winner.
Great Britain will have high hopes of a gold medal in both races as Alistair Brownlee and Helen Jenkins won the men's and women's titles at the 2011 World Triathlon Championship.
Why is it good for you?
The 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 2720 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.
Can you compete?
Get your performance under pressure analysed in just 20 minutes by four-time Olympic gold medallist Michael Johnson
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
Want to get involved with sport in your local community? Why not Join In ?
'Join In Local Sport'
aims to get as many people as possible to turn up and take part in activities at their local sports facilities on
18/19 August, 2012
- the first weekend between the Olympic and Paralympic Games.
The aim of the initiative is for every sports club and community group in the UK to put on a special event in a bid to encourage more people to get involved as members, supporters or volunteers.
More than 4,000 local sports clubs will be opening their doors to host events and show people just how they can get involved.
As well as tips on playing sport there will be information on coaching, supporting and how to help out.
Find an event
The competition format at London 2012
- Hyde Park is the venue for both triathlon events. On Saturday 4 August, 55 women will compete, with 55 men racing on Tuesday 7 August.
- There are no heats: both the men's and women's events consist of a single race.
- Each race will be preceded by a draw in which the top 10 athletes in the International Triathlon Union rankings choose their starting positions on the pontoon from where competitors begin the swim.
- The remaining 45 competitors in each race then publicly draw their positions which are automatically displayed on the screen.
- First up is a 1500m swim in the Serpentine lake followed by a seven-lap, 43km bike ride around a course that takes in Buckingham Palace, and ending with a four-lap, 10km run around the Serpentine.
- The first athlete to cross the finish line wins the gold medal.
More on the London 2012 website
The rules at London 2012
Triathlon races combine swimming, cycling and running, with a 'transition area' in which each athlete is allocated an area for the storage of clothing and equipment when changing between disciplines.
The race is completed without any breaks between disciplines, with the time athletes spend in the transition area counting toward their overall time.
Great Olympic moment
Brigitte McMahon of Switzerland won triathlon's first Olympic gold medal in 2000, beating local favourite Michellie Jones of Australia in a sprint finish in Sydney
In the swim, athletes are allowed to use any stroke they wish. Swimsuits are not allowed to be used if the temperature is above 20C and are mandatory when the temperature is below 14C.
In the cycle, athletes are not allowed to block other athletes or move forward without being in possession of the bike.
By the time the athletes begin the run, they must have left their cycling helmet in the transition area.
Punishments for rule infringements range from a verbal warning to expulsion. Certain rule infringements lead to an athlete getting a yellow card and a time penalty that is carried out in a penalty box.
For example, a 15-second time penalty can be imposed on athletes for minor infringements such as not placing their cycle helmet or goggles in the designated box during transition.
In Beijing, athletes served their penalties in the transition area (eg. between the swim and bike phases), but in London they will be forced to go to a designated penalty box - around 100m away from the transition area - at some point.
This rule change has been designed to ensure infringements are more costly.
More on the Team GB website
Ones to watch
For Team GB, the Brownlee brothers,
are the two best male triathletes in the world and could be locked in a head-to-head battle for gold.
won her second world title in 2011 and has made a promising start to 2012.
was world champion in 2008 and 2010 and remains the main threat to a Brownlee one-two.
In the women's race, Jenkins's biggest rivals are likely to come from the southern hemisphere, in the shape of New Zealand's
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?
Despite being strongly tipped to win gold in both races in London, Great Britain are yet to claim a medal in the triathlon at the Olympics
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 full medal debut at the 2000 Sydney Games.
In 1994, the IOC announced that the sport had formally become part of the Olympic programme and it made its debut at the Sydney Games in 2000, where 500,000 spectators watched the event over the two days.
More on the IOC website