Liu Xiang of China is seen after the women's 50m freestyle semifinal swim-off at FINA World Championships in Gwangju, South Korea, on July 27, 2019. (Xinhua/Wang Jingqiang)

Liu Xiang (1st L) of China is interviewed after the women's 50m freestyle semifinal at FINA World Championships in Gwangju, South Korea, on July 27, 2019. (Xinhua/Wang Jingqiang)

Bronze medalist Ariarne Titmus of Australia competes during the women's 800m freestyle final at FINA World Championships in Gwangju, South Korea, on July 27, 2019. (Xinhua/Tao Xiyi)

Bronte Campbell (R) of Australia hugs Liu Xiang of China after the women's 50m freestyle semifinal swim-off at FINA World Championships in Gwangju, South Korea, on July 27, 2019. (Xinhua/Wang Jingqiang)

Players start during the men's 100m butterfly final at FINA World Championships in Gwangju, South Korea, on July 27, 2019. (Xinhua/Tao Xiyi)

Players start during the women's 200m backstroke final at FINA World Championships in Gwangju, South Korea, on July 27, 2019. (Xinhua/Tao Xiyi)

Liu Xiang (R) of China and Bronte Campbell of Australia get ready before the women's 50m freestyle semifinal swim-off at FINA World Championships in Gwangju, South Korea, on July 27, 2019. (Xinhua/Wang Jingqiang)

Gold medalist Caeleb Dressel of the United States celebrates after the men's 100m butterfly final at FINA World Championships in Gwangju, South Korea, on July 27, 2019. (Xinhua/Wang Jingqiang)

Suo Ran of China gets ready before the women's 50m breaststroke semifinal at FINA World Championships in Gwangju, South Korea, on July 27, 2019. (Xinhua/Wang Jingqiang)

Suo Ran (1st L) of China is seen after the women's 50m breaststroke semifinal at FINA World Championships in Gwangju, South Korea, on July 27, 2019. (Xinhua/Wang Jingqiang)

Swimmers of the United States celebrate after the mixed 4x100m freestyle relay final at FINA World Championships in Gwangju, South Korea, on July 27, 2019. Team of the United States set a new world record with 3 minutes 19.40 seconds. (Xinhua/Bai Xuefei)

Kyle Chalmers of Australia competes during the mixed 4x100m freestyle relay final at FINA World Championships in Gwangju, South Korea, on July 27, 2019. Team of the United States set a new world record with 3 minutes 19.40 seconds. (Xinhua/Bai Xuefei)

Caeleb Dressel (Front L) of the United States and Kyle Chalmers of Australia (Front R) start during the mixed 4x100m freestyle relay final at FINA World Championships in Gwangju, South Korea, on July 27, 2019. Team of the United States set a new world record with 3 minutes 19.40 seconds. (Xinhua/Bai Xuefei)

Caeleb Dressel (L) of the United States and Kyle Chalmers of Australia compete during the mixed 4x100m freestyle relay final at FINA World Championships in Gwangju, South Korea, on July 27, 2019. Team of the United States set a new world record with 3 minutes 19.40 seconds. (Xinhua/Bai Xuefei)

Liu Xiang (R) of China and Bronte Campbell of Australia get ready before the women's 50m freestyle semifinal swim-off at FINA World Championships in Gwangju, South Korea, on July 27, 2019. (Xinhua/Bai Xuefei)

Liu Xiang of China is seen before the women's 50m freestyle semifinal at FINA World Championships in Gwangju, South Korea, on July 27, 2019. (Xinhua/Bai Xuefei)

Liu Xiang (R) of China and Bronte Campbell of Australia starts during the women's 50m freestyle semifinal swim-off at FINA World Championships in Gwangju, South Korea, on July 27, 2019. (Xinhua/Bai Xuefei)

Gold medalist Caeleb Dressel (C) of the United States, silver medalist Andrei Minakov (L) of Russia and bronze medalist Chad Le Clos of South Africa pose for photos after the awarding ceremony of the men's 100m butterfly final at FINA World Championships in Gwangju, South Korea, on July 27, 2019. (Xinhua/Wang Jingqiang)

Gold medalist Caeleb Dressel of the United States starts during the men's 50m freestyle final at FINA World Championships in Gwangju, South Korea, on July 27, 2019. (Xinhua/Bai Xuefei)

Gold medalist Caeleb Dressel of the United States starts during the men's 50m freestyle final at FINA World Championships in Gwangju, South Korea, on July 27, 2019. (Xinhua/Bai Xuefei)

Gold medalist Sarah Sjoestroem of Sweden checks on the results after the women's 50m butterfly final at FINA World Championships in Gwangju, South Korea, on July 27, 2019. (Xinhua/Tao Xiyi)

Gold medalists, team of the United States pose for photos after the mixed 4x100m freestyle relay final at FINA World Championships in Gwangju, South Korea, on July 27, 2019. Team of the United States set a new world record with 3 minutes 19.40 seconds. (Xinhua/Wang Jingqiang)

Gold medalist Katie Ledecky (C) of the United States, silver medalist Simona Quadarella (L) of Italy and bronze medalist Ariarne Titmus of Australia pose for photos after the women's 800m freestyle final at FINA World Championships in Gwangju, South Korea, on July 27, 2019. (Xinhua/Wang Jingqiang)

Swimmers of the United States celebrate after the mixed 4x100m freestyle relay final at FINA World Championships in Gwangju, South Korea, on July 27, 2019. Team of the United States set a new world record with 3 minutes 19.40 seconds. (Xinhua/Bai Xuefei)

Gold medalist Regan Smith (C) of the United States, silver medalist Kaylee McKeown (L) of Australia and bronze medalist Kylie Masse of Canada pose for photos after the women's 200m backstroke final at FINA World Championships in Gwangju, South Korea, on July 27, 2019. (Xinhua/Wang Jingqiang)

Gold medalist Caeleb Dressel of the United States swims in the diving pool after the men's 50m freestyle final at FINA World Championships in Gwangju, South Korea, on July 27, 2019. (Xinhua/Tao Xiyi)

Gold medalist Caeleb Dressel of the United States prepares before the men's 50m freestyle final at FINA World Championships in Gwangju, South Korea, on July 27, 2019. (Xinhua/Bai Xuefei)

Xu Jiayu of China reacts after the men's 50m backstroke semifinal at FINA World Championships in Gwangju, South Korea, on July 27, 2019. (Xinhua/Tao Xiyi)

Gold medalist Katie Ledecky of the United States competes during the women's 800m freestyle final at FINA World Championships in Gwangju, South Korea, on July 27, 2019. (Xinhua/Bai Xuefei)

Wang Jianjiahe (R) of China competes during the women's 800m freestyle final at FINA World Championships in Gwangju, South Korea, on July 27, 2019. (Xinhua/Bai Xuefei)

Wang Jianjiahe (R) of China competes during the women's 800m freestyle final at FINA World Championships in Gwangju, South Korea, on July 27, 2019. (Xinhua/Bai Xuefei)

Gold medalist Katie Ledecky of the United States competes during the women's 800m freestyle final at FINA World Championships in Gwangju, South Korea, on July 27, 2019. (Xinhua/Xia Yifang)

Gold medalist Sarah Sjoestroem (2nd L) of Sweden gets ready before the women's 50m butterfly final at FINA World Championships in Gwangju, South Korea, on July 27, 2019. (Xinhua/Wang Jingqiang)

Gold medalist Sarah Sjoestroem of Sweden celebrates after the women's 50m butterfly final at FINA World Championships in Gwangju, South Korea, on July 27, 2019. (Xinhua/Wang Jingqiang)

Suo Ran of China reacts after the women's 50m breaststroke semifinal at FINA World Championships in Gwangju, South Korea, on July 27, 2019. (Xinhua/Bai Xuefei)

Suo Ran of China starts during the women's 50m breaststroke semifinal at FINA World Championships in Gwangju, South Korea, on July 27, 2019. (Xinhua/Bai Xuefei)

Gold medalist Regan Smith of the United States competes during the women's 200m backstroke final at FINA World Championships in Gwangju, South Korea, on July 27, 2019. (Xinhua/Xia Yifang)

Gold medalist Regan Smith of the United States competes during the women's 200m backstroke final at FINA World Championships in Gwangju, South Korea, on July 27, 2019. (Xinhua/Xia Yifang)

Gold medalist Caeleb Dressel of the United States gets ready before the men's 50m freestyle final at FINA World Championships in Gwangju, South Korea, on July 27, 2019. (Xinhua/Wang Jingqiang)

Gold medalist Caeleb Dressel (R) of the United States prepares before the men's 50m freestyle final at FINA World Championships in Gwangju, South Korea, on July 27, 2019. (Xinhua/Wang Jingqiang)

Bronte Campbell (Rear) of Australia hugs Liu Xiang of China after the women's 50m freestyle semifinal swim-off at FINA World Championships in Gwangju, South Korea, on July 27, 2019. (Xinhua/Tao Xiyi)

Bronte Campbell (Top) of Australia and Liu Xiang of China react after the women's 50m freestyle semifinal swim-off at FINA World Championships in Gwangju, South Korea, on July 27, 2019. (Xinhua/Tao Xiyi)

Bronte Campbell (Top) of Australia and Liu Xiang of China compete during the women's 50m freestyle semifinal swim-off at FINA World Championships in Gwangju, South Korea, on July 27, 2019. (Xinhua/Tao Xiyi)

Silver medalist Kaylee McKeown of Australia competes during the women's 200m backstroke final at FINA World Championships in Gwangju, South Korea, on July 27, 2019. (Xinhua/Xia Yifang)

Bronze medalist Kylie Masse of Canada competes during the women's 200m backstroke final at FINA World Championships in Gwangju, South Korea, on July 27, 2019. (Xinhua/Xia Yifang)

Silver medalist Simona Quadarella of Italy competes during the women's 800m freestyle final at FINA World Championships in Gwangju, South Korea, on July 27, 2019. (Xinhua/Tao Xiyi)