Men's 100m Freestyle
· At each of the last four World Championships, this event was won by a swimmer under the age of 23.
· The defending champion is Ning Zetao (CHN), the first from his country to win or even collect a medal in this event at World Championships or Olympic Games.
· The previous two world titles were claimed by James Magnussen (AUS), who became the fourth swimmer to win this event at back-to-back World Championships, joining Matt Biondi (USA), Aleksandr Popov (RUS) and Filippo Magnini (ITA).
· Following his double in 1994-1998, Popov added another title in 2003, making him the only man to have won this event three times in the competition. In 2003, Popov was the only swimmer over 30 ever to win this event.
· The United States leads the way with six world titles in this event, amassed by five different swimmers. Seven other countries have won this, but never thanks to more than one individual swimmer.
· At the Rio 2016 Olympic Games, the gold medal in this event was won by 18-year-old Kyle Chalmers (AUS), the youngest winner of this event at Olympic Games or World Championships since Jörg Woithe won it at age 17 at the Moscow 1980 Olympic Games.
· The last reigning Olympic champion to take gold at the following World Championships was Aleksandr Popov in 1998.
· The last person to win this event in a back-to-back major (Olympic and World Championships combined) edition was Magnini, who won gold at the World Championships in 2005 and 2007.
· In 2009 in Rome, this event was won by Cesar Cielo (BRA) in a world record time (46.91) that still stands today.
· Cielo's effort marked the first and only time the world record in this event was improved at the World Championships.
· Pieter Timmers (BEL) finished runner-up in Rio a year ago and became the first swimmer from Belgium to claim a medal in this event at Olympic Games or World Championships.
· Nathan Adrian (USA) has won three medals (G1-S0-B2) in this event at world championships or Olympic Games. Only three swimmers have won more Popov (G5-S1-B0), Pieter van den Hoogenband (NED, G2-S2-B0) and Jim Montgomery (USA, G2-S1-B1).
· No US swimmer has won the men's 100m freestyle at the World Championships since Anthony Ervin (USA) in 2001. Team USA has not won this in their last seven attempts, after producing the champion in six of their first nine.
· The United States has won 43 medals (G19-S13-B11) in this event at Olympic Games or World Championships, twenty-six more than the next most prolific country, Australia on 17 (G6-S6-B5).
Women's 50m Backstroke
· Reigning women's 50m backstroke world champion Fu Yuanhui (CHN) is hoping to become the second woman to win this title twice, after compatriot Zhao Jing (CHN, 2009 and 2013).
· At the last two World Championships two Chinese women finished on the podium of the 50m backstroke: Fu (gold) and Liu Xiang (bronze) in 2015 and Zhao (gold) and Fu (silver) in 2013.
· Fu (G1-S1-B0) hasthechance to claim a record third medal in this event at the World Championships.
· The last European woman to finish on the podium in the 50m backstroke was Anastasiia Fesikova (RUS) when she won the world title in 2011.
· Emily Seebohm (AUS) and Holly Barratt (AUS) are hoping to join Tayliah Zimmer (bronze in 2007) and Giaan Rooney (gold in 2005) as the only Australian woman with a World Championships medal in this event.
· Seebohm can become the third woman with a World Championships medal in the 50m, 100m and 200m backstroke, after Missy Franklin (USA) and Anastasiia Fesikova. Seebohm has already claimed the medal set in the 100m (gold 2015, silver 2013, bronze 2009) and won the 200m backstroke world title in 2015.
Women's 200m Butterfly
· Mireia Belmonte (ESP) won the women's 200m butterfly at the Rio 2016 Olympic Games. She can become the first reigning Olympic champion to claim the world title in this event since Otylia Jedrzejczak (POL) won in 2005 after winning Olympic gold in Athens in 2004.
· The only swimmers to win a world title for Spain are Nina Zhivanevskaya (2003, 50m backstroke) and Martin López-Zubero (1991 200m backstroke; 1994 100m backstroke).
· Belmonte has already claimed a medal in the 200m butterfly at the World Championships, as she finished second behind Liu Zige (CHN) in 2013.
· Reigning 200m butterfly world champion Natsumi Hoshi (JPN) will not defend her title as she has retired from professional swimming after taking the bronze medal in this event at the Olympic Games in Rio de Janeiro.
· Silver medallist in Rio de Janeiro Madeline Groves (AUS) will also be absent from the World Championships.
· Katinka Hosszú finished on the podium in this event at the 2009 and 2013 World Championships (two bronze medals). She could claim a record-equalling third medal in the women's 200m butterfly, alongside Jessicah Schipper (AUS), Otylia Jedrzejczak and Liu Zige.
· Hosszú can become the first woman to claim a World Championship gold medal in this event in front of a home crowd since Jiao Liuyang (CHN) in Shanghai in 2011.
· China is the only country to have been represented on the podium of the women's 200m butterfly at each of the last four World Championships. Liu Zige completed the medal set with silver in 2009, bronze in 2011 and gold in 2013, while Jiao Liuyang (gold in 2011) and Zhang Yufei (bronze in 2015) also claimed medals.
Men's 200m Individual Medley
· This event will produce a first-time winner as the winner of this event at the last four World Championships, Ryan Lochte (USA), will not participate. Michael Phelps (USA), who won this event in 2003, 2005 and 2007, has retired.
· At the first nine World Championships, no swimmer representing the United States had won this event, before Phelps and Lochte started their gold rush.
· This puts the US at the top of the medal table in this event, with seven gold medals. Hungary is next on three gold medals, two by Tamás Darnyi (HUN) and one by András Hargitay (HUN).
· At World Championships and Olympic Games combined the last 11 finals in this event were won by either Phelps or Lochte. The last to win this other than these two was Massimiliano Rosolino (ITA) at the 2001 World Championships in Fukuoka.
· Phelps won this event for the first time at age 18 at the 2003 World Championships in Barcelona and completed his farewell tour by winning it at age 31 at the Rio 2016 Olympic Games.
· Lochte also won his last major title in this event at age 31, when he won the 200m individual medley at the 2015 World Championships in Kazan.
· At the World Championships, this event has never been won by a swimmer performing in front of a home crowd.
· At the World Championships and Olympic Games combined, László Cseh (HUN) has won six medals (S3-B3) in this event, but never a gold.
· Wang Shun (CHN) came third in this event at the Rio 2016 Olympic Games and the 2015 World Championships. No Asian swimmer has ever won this event at the worlds.
Mixed 4 x 100m Medley Relay
· At the 2015 FINA World Championships the mixed 4x100m medley relay event was held for the first time at the World Championships.
· Great Britain won the inaugural edition of this event, ahead of United States (silver) and Germany (bronze).
· Coming into these World Championships this is the only relay event (men, women, mixed) the United States has not won at the World Championships.
· Great Britain also won both European titles in this event (2014 and 2016), with the other four medals at those European Championships being divided among four countries: Netherlands, Russia, Italy and Hungary.
· Coming into this tournament Great Britain has not claimed multiple gold medals in any relay event at the World Championships. Great Britain's other relay world titles came in the women's 4x200m freestyle relay (2001) and the men's 4x200m freestyle relay (2015).
· Before these World Championships Germany's last gold medal in a relay event came at the 2001 World Championships in Fukuoka when it won the women's 4x100m freestyle relay event.