Pool swimming at the Olympic Games takes place inside a 50-meter-long swimming pool divided into eight lanes. Swimmers race each other at varying distances using one (or all, for medley events) of four strokes: freestyle, backstroke, breaststroke and butterfly. All swimmers competing in a given race start simultaneously at the sound of a tone. The winner is the first to touch the wall of the pool after swimming the set distance, which can be as short as 50m (one lap) or as long as 1500m (30 laps).
There are 17 total Olympic swimming events per gender. New to the Olympic program for Tokyo is a mixed medley relay, which will include teams of two male and two female swimmers per country.
For freestyle, breaststroke, butterfly and IM events, swimmers begin by diving into the water from an elevated starting platform. On the starter's command, "take your mark," each swimmer assumes a starting position, arched over the knees and grasping the front edge of the platform. When all swimmers are still, the starter activates an electronic tone to start the race, and the competitors dive into the pool. Once in the water, a swimmer's head must break the surface within the first 15 meters.
In swimming, there are no "false start" warnings. Any swimmer who dives into the pool before the starting signal is automatically disqualified. If the starting signal sounds before the disqualification is declared, the race continues, and the swimmer is disqualified when the race is over.
For backstroke events, as well as the start of the medley relays, swimmers start in the water, facing the wall of the pool. They grasp a bar underneath the starting platform with both hands, and place both feet on the FINA-approved "backstroke ledge,” which dangles on the wall below the surface. When the race starts, swimmers dive backwards, launching themselves off the wall.
Quick turns are essential to a good race (with the exception of the 50m freestyle, which is only one length of the pool). In every event, swimmers must make contact with the wall as they turn. In freestyle and backstroke, swimmers may somersault as they reach the wall, touching it only with their feet. In butterfly and breaststroke, swimmers must touch the wall with both hands simultaneously before executing the turn. Just like after the start, swimmers must resurface and make a stroke within the first 15m after making a turn.
There are some major differences between how swimmers approach the different races of the Olympic program. The sprint races (50m and 100m) are all-out scrambles from start to finish, sometimes referred to as the "splash and dash". The slightest mistake can cost a swimmer a fraction of a second, and thus the race.
The 200m events require swimmers to have a sense of pace as well as the ability to swim a controlled sprint. This distance is considered by many to be the most difficult to master.
The distance events – the 400m, 800m, and 1500m freestyles – require swimmers to constantly be aware of their position in a race and to closely monitor their fatigue. Swimming the first portion of the race too fast can sap a swimmer's strength and cause a poor finish, while swimming the first portion too slowly can create a deficit impossible to make up.
Swimming becomes a true team sport during relay events. Countries field teams of four swimmers, all of whom must swim one-fourth the total length of the race. The second swimmer is only able to begin his/her leg once the first swimmer touches the wall to complete theirs, and so on. The winner is the country who’s fourth-leg swimmer touches the wall before any other country’s fourth-leg swimmer.
Relays are contested over a prelim and a final. The athletes who swim in the final do not necessarily need to be the same ones who swam the prelim. Strong swimming nations often bring “relay-only” swimmers to the Olympics to swim in the prelims but not the final, in order to keep the best four swimmers rested. Relay prelim swimmers do qualify for a medal should their country win one in the final, meaning as many as eight athletes can win a gold medal in each relay event.
There are seven total relay events at the Tokyo Games – two freestyle relays per gender (4x100m and 4x200m), one medley relay per gender, and a mixed relay, which makes its debut as an Olympic event in Tokyo.
The 10k open water event is held in a natural body of water and follows a wide course with no lane restrictions. Incidental contact between swimmers is permitted and expected, especially during the mass start, when all 25 competitors set off together.
During the 10k competition, each athlete must wear a wristband known as a transponder, which is linked to the timing and results system. Athletes can be disqualified for pacing, slipstreaming, walking or jumping, or finishing without their transponder. The athletes are also identified by temporary tattoos or markers on their upper arms, shoulder blades and wrists.