Britain's Francesca Halsall (front) reacts next to Christine Magnuson of the U.S. after competing in the women's 50m butterfly semi-final during the World Swimming Championships at the Sant Jordi arena in Barcelona August 2, 2013. REUTERS/Michael Dalder (SPAIN - Tags: SPORT SWIMMING)

Christine Magnuson of the U.S. competes in the women's 50m freestyle semifinal during the FINA World Swimming Championships in Istanbul December 15, 2012. REUTERS/Murad Sezer (TURKEY - Tags: SPORT SWIMMING)

U.S. team Olivia Smoliga, Laura Sogar, Christine Magnuson and Lia Neal look at the scoreboard after the women's 4x100m medley relay heats during the FINA World Swimming Championships in Istanbul December 14, 2012. REUTERS/Murad Sezer (TURKEY - Tags: SPORT SWIMMING)

Christine Magnuson (R) of the U.S. looks at the scoreboard past Jeanette Ottesen Gray of Denmark after competing at women's 50m butterfly semi-final during the FINA World Swimming Championships in Istanbul December 13, 2012. REUTERS/Murad Sezer (TURKEY - Tags: SPORT SWIMMING)

Christine Magnuson of the U.S. looks at the scoreboard after competing at women's 50m butterfly semi-final during the FINA World Swimming Championships in Istanbul December 13, 2012. REUTERS/Murad Sezer (TURKEY - Tags: SPORT SWIMMING)

Christine Magnuson celebrates after winning her women's 50m freestyle semifinal during the U.S. Olympic swimming trials in Omaha, Nebraska, July 1, 2012. REUTERS/Jeff Haynes (UNITED STATES - Tags: SPORT SWIMMING SPORT OLYMPICS)

Christine Magnuson leaves the starting block during the women's 50m freestyle heats at the U.S. Olympic swimming trials in Omaha, Nebraska July 1, 2012. REUTERS/Jeff Haynes (UNITED STATES - Tags: SPORT SWIMMING SPORT OLYMPICS) 

Christine Magnuson, Elizabeth Pelton, Rebecca Soni and Amanda Weir (front L-R) of the U.S. stand together in front of France's Sophie De Ronchi (back L) and other competitors after competing in the women's 4 X 100m medley relay heats at the 14th FINA World Championships in Shanghai July 30, 2011. REUTERS/Christinne Muschi (CHINA - Tags: SPORT SWIMMING AQUATICS) 

Winner Dana Vollmer of the U.S. hugs teammate Christine Magnuson (L) after the women's 100m butterfly final at the Pan Pacific 2010 swimming championships in Irvine, California, August 20, 2010. REUTERS/Christinne Muschi (UNITED STATES - Tags: SPORT SWIMMING) 

Christine Magnuson celebrates her victory in the women's 100m butterfly at the U.S. National Swimming Championships in Irvine, California August 3, 2010. REUTERS/Mike Blake (UNITED STATES - Tags: SPORT SWIMMING) 

Sarah Sjostrom of Sweden (R) reacts, beside Christine Magnuson of the U.S., after setting a new world record in the women's 100m butterfly swimming semi-final at the World Championships in Rome July 26, 2009. REUTERS/Alessandro Bianchi (ITALY SPORT SWIMMING) 

Christine Magnuson of the U.S. competes in the women's 100m butterfly swimming heats at the World Championships in Rome July 26, 2009. REUTERS/Tony Gentile (ITALY SPORT SWIMMING) 

US swimmer Dana Vollmer (R) hugs third place finisher Christine Magnuson after Vollmer won the women's 100m freestyle final at the USA Swimming National Championships in Indianapolis, Indiana, July 11, 2009. REUTERS/Gary Hershorn (UNITED STATES SPORT SWIMMING) 

U.S. swimmer Christine Magnuson swims on her way to winning the women's 100m butterfly event at the USA Swimming National Championships in Indianapolis, Indiana July 7, 2009. REUTERS/Brent Smith (UNITED STATES SPORT SWIMMING) 

U.S. swimmer Christine Magnuson waves to the crowd after she won the Women's 100m Butterfly event at the USA Swimming National Championships in Indianapolis, Indiana, July 7, 2009. REUTERS/Gary Hershorn (UNITED STATES SPORT SWIMMING) 

U.S. swimmer Christine Magnuson (R) hugs compatriot Dana Vollmer after Magnuson won the women's 100m butterfly event at the USA Swimming National Championships in Indianapolis, Indiana July 7, 2009. REUTERS/Gary Hershorn (UNITED STATES SPORT SWIMMING) 

Christine Magnuson of the U.S. swims during her Women's 100m Butterfly preliminary heat at the USA Swimming National Championships in Indianapolis, Indiana, July 7, 2009. REUTERS/Christinne Muschi (UNITED STATES SPORT SWIMMING) 

(L-R) Silver medallists Natalie Coughlin, Rebecca Soni, Christine Magnuson and Dara Torres of the U.S. pose with gold medallists Emily Seebohm, Leisel Jones, Lisbeth Trickett and Jessicah Schipper of Australia after the women's 4x100m medley relay swimming final at the National Aquatics Center during the Beijing 2008 Olympic Games August 17, 2008. REUTERS/Kai Pfaffenbach (CHINA) 

(L-R) Natalie Coughlin, Rebecca Soni, Christine Magnuson and Dara Torres of the U.S. pose with their silver medals for the women's 4x100m medley relay final at the National Aquatics Center during the Beijing 2008 Olympic Games August 17, 2008. REUTERS/David Gray (CHINA) 

(L-R) Silver medallist Christine Magnuson of the U.S., gold medallist Lisbeth Trickett of Australia and bronze medallist Jessicah Schipper of Australia show their medals on the podium after the women's 100m butterfly swimming final at the National Aquatics Centre during the Beijing 2008 Olympic Games, August 11, 2008. REUTERS/Jerry Lampen (CHINA) 

Christine Magnuson of the U.S. holds up her silver medal after the women's 100 meters butterfly swimming final at the National Aquatics Center during the Beijing 2008 Olympic Games August 11, 2008. REUTERS/Wolfgang Rattay (CHINA) 

Gold medallist Lisbeth Trickett (C) of Australia celebrates with silver medallist Christine Magnuson (L) of the U.S. and bronze medallist Jessicah Schipper (R) of Australia after the women's 100 meters butterfly swimming final during the Beijing 2008 Olympic Games at the National Aquatics Center August 11, 2008. REUTERS/Wolfgang Rattay (CHINA) 

Gold medallist Lisbeth Trickett (C) of Australia celebrates with silver medallist Christine Magnuson (L) of the U.S. and bronze medallist Jessicah Schipper (R) of Australia after the women's 100 meters butterfly swimming final during the Beijing 2008 Olympic Games at the National Aquatics Center August 11, 2008. REUTERS/David Gray (CHINA) 

Lisbeth Trickett (C) of Australia swims to a gold medal next to Christine Magnuson (L) of the U.S. and Jessicah Schipper (R) of Australia in the women's 100 meters butterfly final at the National Aquatics Center during the Beijing 2008 Olympic Games August 11, 2008. Picture taken with underwater camera. REUTERS/Wolfgang Rattay (CHINA) 

Christine Magnuson swims to a win in the Women's 100m Butterfly at the U.S. Olympic Swimming Trials in Omaha, Nebraska, June 30, 2008. REUTERS/Christinne Muschi (UNITED STATES) (BEIJING OLYMPICS 2008 PREVIEW) 

Christine Magnuson celebrates her win in the Women's 100m Butterfly at the victroy podium at the U.S. Olympic Swimming Trials in Omaha, Nebraska, June 30, 2008. REUTERS/Jeff Haynes (UNITED STATES) (BEIJING OLYMPICS 2008 PREVIEW) 

Christine Magnuson celebrates her win in the Women's 100m Butterfly at the U.S. Olympic Swimming Trials in Omaha, Nebraska, June 30, 2008. REUTERS/Christinne Muschi (UNITED STATES) (BEIJING OLYMPICS 2008 PREVIEW) 

Christine Magnuson smiles as she looks at the scoreboard following her heat in the Women's 100m Butterfly at the U.S. Olympic Swimming Trials in Omaha, Nebraska, June 29, 2008. REUTERS/Christinne Muschi (UNITED STATES) (BEIJING OLYMPICS 2008 PREVIEW)