Preview: Men's swimming
Men's 400m Freestyle
· Sun Yang (CHN) has won the men's 400m freestyle in each of the last two World Championships editions, in Barcelona in 2013 and in Kazan in 2015.
· Sun is one of those four swimmers who have won this event more than once at the World Championships and can become the second in history to win a third.
· Ian Thorpe (AUS) won the men's 400m freestyle at three successive World Championships, in Perth in 1998, in Fukuoka in 2001 and in Barcelona in 2003.
· Two other swimmers have won two world titles in this event: Vladimir Salnikov (URS) and Park Tae-Hwan (KOR).
· Sun and Park have claimed four out of the last five world titles in this event. The only non-Asian swimmer to win it since 2007 was Paul Biedermann (GER) in Rome in 2009.
· In Rome, Biedermann took the world record in this distance, a mark that still stands today (3:40:07). Ian Thorpe had held it for nearly 10 years and registered five world record improvements in the men's 400m freestyle.
· Prior to Park's first victory of 2007 in this event it had been claimed by an Australian at five successive World Championships, most recently by Grant Hackett (AUS) in 2005.
· At the first two World Championships (1973 and 1975), men's 400m freestyle was won by swimmers representing the United States. No US swimmer has won it ever since.
· Ian Thorpe won his first world title in this event on 15 January 1998, when he was 15 years and 94 days old. He is still the youngest world champion ever in a men's event.
· At the Rio 2016 Olympic Games, this event was won by 20-year-old Mack Horton (AUS). Each of the last three world titles in this event were won by the reigning Olympic champion.
· Aleksandr Krasnykh (RUS) could win the first medal for Russia in this event since 2007, when Yuri Prilukov took bronze.
· At the World Championships and Olympic Games combined, United States and Australia have won this event 11 times each. No other country has won it more than three times.
Men's 100m Breaststroke
· Adam Peaty (GBR) claimed the world title in the men's 100m breaststroke in 2015 and could become the third multi-gold medallist in this event after Brendan Hansen (USA) and Norbert Rózsa (HUN).
· Hansen (2005-2007) and Rózsa (1991-1994) both claimed their two world titles in this event in successive world championships.
· At the Rio 2016 Olympic Games, the men's 100m breaststroke was won by Peaty. The last time the world title in this event was won by the reigning Olympic champion was in 1998, when Fred Deburghgraeve (BEL) added world gold to his Olympic title.
· Peaty and Ross Murdoch (GBR) are aiming for a one-two finish for Great Britain. The last country to claim both silver and gold in the men's 100m breaststroke event in a single edition of the World Championships was Hungary in 1994, when Rózsa and Károly Güttler (HUN) finished first and second respectively.
· Cameron van der Burgh (RSA) has collected four World Championships medals in the men's 100m breaststroke event (G0-S2-B2), more than any other swimmer.
· Van der Burgh has reached the podium in this event in each of the last four editions of the World Championships (2009-2015).
· Van der Burgh (29) could become the oldest medallist in this event in history of the World Championships. Felipe Lima (BRA) currently holds the record, as he was 28 years old when he earned bronze in 2013.
· Russia last won a medal in this event in 2001, when Roman Sludnov (RUS) won the world title in Fukuoka, Japan.
· Yasuhiro Koseki (JPN) could become the first swimmer from Japan to collect a medal in this event at the World Championships since Kosuke Kitajima (JPN) in 2007 (silver).
Men's 50m Butterfly
· Reigning world champion Florent Manaudou (FRA) will not compete as he has switched sports and is trying out handball.
· Roland Schoeman (RSA, 2005-2007) and Cesar Cielo (BRA, 2011-2013) both claimed two world titles in this event in back-to-back editions.
· Ian Crocker (USA, G0-S3-B0) has won most medals in this event.
· Konrad Czerniak (POL) is hoping to become the first swimmer from Poland to become world champion in any men's event since 2007, when Mateusz Sawrymowicz (POL) won gold in the men's 1500m freestyle.
· Andrii Govorov (UKR) could become the third reigning European champion in the men's 50 butterfly to win the world title in the same event after Milorad Cavic (SRB) in 2009 and Manaudou in 2015.
· Govorov and reigning world junior champion Andriy Khloptsov (UKR) could both become the first swimmers representing Ukraine to collect a world championships medal in this event since Sergiy Breus (UKR) in 2005 (bronze).
· United States have only won silver medals in this event, four in total.
· The world record in this event belongs to Rafael Muñoz (ESP), the only one in long course held by a swimmer from Spain.
Men's 4 x 100m Freestyle Relay
· France have won this event at each of the previous two world championships, in 2013 and 2015. Prior to 2013, France had never won this event at the worlds.
· Three French swimmers were part of both victorious campaigns: Fabien Gilot (FRA), Jérémy Stravius (FRA) and Florent Manadou (FRA).
· Five different swimmers have won a joint-record three world titles in this event. All of them represented United States: Jim Montgomery (USA), Tom Jager (USA), Neil Walker (USA), Michael Phelps (USA) and Garrett Weber-Gale (USA).
· United States last won this event at the world championship in Rome in 2009. In 2011 and 2013 they won a medal in it of lesser value than gold. In 2015, they failed to make it past the heats, slumping to 11th place.
· At the Rio 2016 Olympic Games, United States won gold, edging France for the gold. The French team consisted of their nucleus of Gilot, Manaudou and Stravius with Mehdy Metella (FRA) swimming the opening leg in the final.
· Team USA won this event at each of the first eight world championships, but have won it at only three of the next eight.
· Apart from United States (11 times), France (2013, 2015) and Australia (2001, 2011), Russia is the fourth country that has won this event (2003).
· United States have won 14 medals in this event, eight more than Australia and France, who are both on six.
· Apart from 2015, the US did not win a medal in Fukuoka in 2001, when the team was disqualified for using a swimmer who was not on the entry list.
· The world record in this event was set in the Olympic final in 2008, when US were anchored by Jason Lezak, who swam a blistering 46.06 split to run down France's Alain Bernard to give the US the gold.
Women's 4 x 100m Freestyle Relay - Swimming
· Australia are the reigning Olympic and world champions in the women's 4x100m freestyle relay.
· Australia could become the first nation to win back-to-back world titles in this event since Netherlands in 2009-2011.
· Australia also won the world title in this event in 2007 and 2005. Only United States (5) and East Germany (4) have won this discipline more often.
· United States have claimed a record 15 medals in this event at the world championships (G5-S8-B2) as they only failed to reach the podium in 2009.
· Netherlands are the only country to have finished on the podium in this event at the last five world championships. They won the title in 2009 and 2011, claimed silver in 2015 and took bronze in 2007 and 2013.
· Femke Heemskerk (NED) and Ranomi Kromowidjojo (NED) can both claim a record sixth medal in this event. They now share the record of five with Natalie Coughlin (USA) and Katrin Meissner (GER).
· Heemskerk and Kromowidjojo can also equal Jenny Thompson (USA) on a record three world titles in this event.
· Canada finished in third place in this discipline at the Rio 2016 Olympic Games. They could claim their first world championships medal in this event in almost 40 years, a bronze medal in 1978.
· Across all events, Ledecky has won nine world titles, just two shy from the women's record held by Franklin (11).
· Ledecky won 14 of the 15 events she took part in at Olympic Games and world championships so far. She only failed to win the 4x100m freestyle relay at the Rio 2016 Olympic Games where the US team finished second behind Australia.
· Sarah Sjöström (SWE, 100m butterfly) and Katinka Hosszú (HUN, 400m individual medley) are vying to become the first women with four world titles in an individual event.
· Hosszú won the individual medley double at each of the last two world championships. She could become the first woman to do so three editions in a row.
· In total, Hosszú has claimed nine world championship medals (G5-S0-B4). She is eyeing to become the second swimmer from Hungary to reach double figures, after László Cseh (HUN) who has claimed 12 medals coming into this year's edition (G2-S5-B5).
· Sarah Sjöström has claimed eight medals at the world championships (G4-S3-B1) and is hoping to become the most decorated Swede, male or female, in the history of the tournament. She currently shares the record of eight medals with Therese Alshammar (SWE, G2-S5-B1).
· Ledecky (400m, 800m and 1500m freestyle), Sjöström (100m butterfly) and Hosszú (200m and 400m individual medley) can all win a specific event at three successive world championships. Prior to this tournament no woman has achieved this in an individual event.
· Federica Pellegrini (ITA) has claimed six medals in the women's 200m freestyle (G2-S3-B1). She can become the first swimmer, male or female, to bag seven medals in an individual event at the world championships. She now shares the record of six with Ryan Lochte (USA, men's 200m individual medley, G4-S1-B1).
· Canada has claimed 18 medals in women's events at the world championships (G0-S4-B14), but are still searching for their first women's world title.