Bring the pain: Olympic swimming begins with grueling 400 IM
Athletes exercise during a swimming training session at the Tokyo Aquatics Centre at the 2020 Summer Olympics, Friday, July 23, 2021, in Tokyo, Japan. (AP Photo/Martin Meissner)

Athletes exercise during a swimming training session at the Tokyo Aquatics Centre at the 2020 Summer Olympics, Friday, July 23, 2021, in Tokyo, Japan. (AP Photo/Martin Meissner)

Jul. 23, 2021 12:27 AM EDT
An athlete exercises during a swimming training session at the Tokyo Aquatics Centre at the 2020 Summer Olympics, Friday, July 23, 2021, in Tokyo, Japan. (AP Photo/Martin Meissner)

An athlete exercises during a swimming training session at the Tokyo Aquatics Centre at the 2020 Summer Olympics, Friday, July 23, 2021, in Tokyo, Japan. (AP Photo/Martin Meissner)

Jul. 23, 2021 12:25 AM EDT
Chase Kalisz of the United States arrives for a swimming practice session at the Tokyo Aquatics Center at the 2020 Summer Olympics, Thursday, July 22, 2021, in Tokyo, Japan. (AP Photo/Matthias Schrader)

Chase Kalisz of the United States arrives for a swimming practice session at the Tokyo Aquatics Center at the 2020 Summer Olympics, Thursday, July 22, 2021, in Tokyo, Japan. (AP Photo/Matthias Schrader)

Jul. 21, 2021 09:45 PM EDT
Athletes exercise during a swimming training session at the Tokyo Aquatics Centre at the 2020 Summer Olympics, Friday, July 23, 2021, in Tokyo, Japan. (AP Photo/Martin Meissner)

Athletes exercise during a swimming training session at the Tokyo Aquatics Centre at the 2020 Summer Olympics, Friday, July 23, 2021, in Tokyo, Japan. (AP Photo/Martin Meissner)

Jul. 23, 2021 12:27 AM EDT