Women's 400m Individual Medley
Katinka Hosszú (HUN) has won the women's 400m individual medley in three of the last four editions of the world championships, only failing in 2011.
Hosszú could become the first woman to claim four medals in the 400m individual medley. She now shares the record of three with Yana Klochkova (UKR) and Stephanie Rice (AUS).
Hosszú's three world titles are already a record in this event.
Hosszú broke the 400m individual medley world record by more than two seconds when she won this event at the Rio 2016 Olympic Games. (4:26.36)
She can become the third woman to win the 400m individual medley world title as the reigning Olympic champion. Klochkova won the 2001 and 2003 world title after her gold medal at Sydney 2000 and Petra Schneider (GDR) won in 1982 after Olympic gold at Moscow 1980.
Hosszú can become the first woman to win this event in front of a home crowd at the world championships.
At the world championships and Olympic Games combined, Hosszú could win this discipline for the fourth consecutive time (after 2013, 2015 world championships and 2016 Olympic Games). Only Klochkova has achieved this: 2000 Olympic Games, 2001 and 2003 world championships, 2004 Olympic games.
Elizabeth Beisel (USA) could become the fourth woman with at least three medals in the 400m individual medley, after Hosszú, Klochkova and Rice. She won the world title in 2011 and took the bronze medal in 2013.
Hannah Miley (GBR, silver in 2011) and Mireia Belmonte (ESP, silver in 2013) are hoping to bag their second world championships medal in this discipline.
Belmonte claimed the bronze medal in this event at the Olympic Games in Rio de Janeiro, while Miley just missed out on a medal in fourth place.
Men's 400m Individual Medley
At each of the previous two world championships (2013 and 2015), the men's 400m individual medley was won by Daiya Seto (JPN).
Seto is one of five swimmers to have won this event at back-to-back world championships, alongside András Hargitay (HUN), Tamás Darnyi (HUN), Tom Dolan (USA) and Ryan Lochte (USA).
One other swimmer has won it twice, however not at successive world championships. Michael Phelps (USA) triumphed in 2003 and 2007.
Hungary has won five gold medals in this event with László Cseh (HUN joining Hargitay and Darnyi as champions. Only United States have won this event more often (7) than Hungary.
Hungarians have won two events five times at world championships: the men's 400m individual medley and the men's 200m breaststroke.
Lochte was the last US swimmer to win this event, when he triumphed in Shanghai in 2011. At 26, he was also the oldest winner of this event at world championships.
Lochte is the only swimmer to have won this event over the age of 23 at world championships.
At the Rio 2016 Olympic Games last summer, this event was won by Kosuke Hagino (JPN), meaning that Japan has now won it at the last three major international competitions (world championships and Olympic Games).
Japan had not won this event at world championships or Olympic Games, before Seto won his first world title in 2013.
Women's 4 x 100m Medley Relay
Four nations have previously won the women's 4x100m medley relay at the world championships: United States (5 wins), China (4), East Germany (4) and Australia (3).
China won this event at the last world championships in Kazan in 2015 and can now win this event at back-to-back championships for the first time. United States (2011-2013), Australia (2005-2007) and East Germany (1973-1975, 1982-1986) already achieved this.
Australia finished on the women's 4 x 100m medley relay podium at each of the last nine editions of the world championships, last failing to do so in 1994 when they finished fourth.
United States have claimed a record 14 medals in this event, but never finished third (5 gold, 9 silver).
United States won the women's 4 x 100m medley relay at the Rio 2016 Olympic Games, ahead of Australia (silver) and Denmark (bronze).
The US women can win this world title as the reigning Olympic champions for the third time, after winning in 2013 (gold at London 2012) and in 1998 (gold at Atlanta 1996).
Denmark could claim their first world championships medal in this event. In 2015 Sweden bagged their first medal in the women's 4x100m medley relay, finishing second.
Emily Seebohm (AUS, G1-S2-B1) could equal Leisel Jones (AUS, G3-S0-B2) and Natalie Coughlin (USA, G1-S4-B0) on a record five medals in this event.
Men's 4 x 100m Medley Relay
Two years ago in Kazan, United States won the gold medal in this event and reclaimed the world title they had lost to France in 2013.
For the US, it was their 12th world title in this event, in 16 world championships. The only other countries that have won this are Australia (three times) and France (once).
United States have won a medal in this event on 13 occasions (G12-S1-B0) of the 16 times it was contested at the world championships. They only missed out in 2001, 2007 and 2013.
Each time the US failed to win a medal in this event it was because their team was disqualified, either in the final (2001, 2013) or in the heats (2007).
The only team to beat United States in a men's medley relay at the world championships in which the US were not disqualified was Australia in front of a home crowd in Perth in 1998.
United States won this event at the Rio 2016 Olympic Games last summer, ahead of Great Britain and Australia.
Five swimmers were part of the US' winning teams in 2015 and 2016: Nathan Adrian (USA), Kevin Cordes (USA), Cody Miller (USA), Ryan Murphy (USA) and Tom Shields (USA).
The star of the previous US generation, Michael Phelps (USA) was on the winning team in this event eight times at world championships and Olympic Games, three times more often than any other swimmer.
Phelps also holds the record at world championships. He is the only swimmer to have won this event four times at the worlds.
Ryan Murphy is the world record holder in the men's 100m backstroke. He set the mark at 51.85 in the opening leg of the men's 4 x 100m medley relay final at the Rio Olympic Games last year.