(Reuters) - The 2020 Tokyo Olympics includes 33 sports. Swimming is one of five aquatic events.
Here are some key facts about Olympic swimming:
Introduced: Swimming featured in the first modern Olympics in 1896, with women’s events added for the 1912 Games.
Events: One of the largest and most popular Olympic sports, swimming involves 35 different events split between men and women plus a mixed-gender relay, which was added this year, but the majority of the events see swimmers compete solo.
As well as the mixed-gender relay, two other events were added to the Tokyo 2020 lineup: the men’s 800 metres freestyle and the women’s 1500 metres freestyle.
Strokes: The four main strokes are freestyle, backstroke, breaststroke and butterfly. Most of the events involve swimmers competing in one particular stroke, such as the 100 metres freestyle or the 200 metres butterfly.
There are also individual and relay medley events that involve one swimmer using all four strokes in different legs of the race, or relay team members each using a different stroke.
Scoring and rules: The fastest swimmer – or team - wins. Touchpad technology tracks when they have finished.
Technique: Precision is key, with swimmers spending years dedicated to completing each stroke with maximum efficiency. Swimmers must work to keep their legs and arms moving in unison on breaststroke and butterfly. On the backstroke, maintaining a consistent direction can be a challenge, as athletes sometimes veer from side-to-side as they face upwards during the swim.
Key athlete: American Michael Phelps is the most decorated Olympian of all time with 28 medals. He retired after his fifth Olympics - the 2016 Rio Games.
Sources: International Olympic Committee, FINA, Tokyo Organising Committee of the Olympic and Paralympic Games, Team USA
Reporting by Amy Tennery; Editing by Ken Ferris