Allyson Felix of the United States competes in the Women's 400 meter semifinal on Day 9 of the Rio 2016 Olympic Games at the Olympic Stadium on August 14, 2016 in Rio de Janeiro, Brazil.

Allyson Felix (R) of the United States, Shaunae Miller of the Bahamas and Libania Grenot of Italy compete in the Women's 400m Semi final on Day 9 of the Rio 2016 Olympic Games at the Olympic Stadium on August 14, 2016 in Rio de Janeiro, Brazil.

Allyson Felix of the United States, Christine Day of Jamaica and Shaunae Miller of the Bahamas compete in the Women's 400 meter semifinal on Day 9 of the Rio 2016 Olympic Games at the Olympic Stadium on August 14, 2016 in Rio de Janeiro, Brazil.

Allyson Felix of the United States and Shaunae Miller of the Bahamas compete in the Women's 400 meter semifinal on Day 9 of the Rio 2016 Olympic Games at the Olympic Stadium on August 14, 2016 in Rio de Janeiro, Brazil.

Sock and shoe detail of Allyson Felix of the United States prior to Women's 400 metres final on Day 10 of the Rio 2016 Olympic Games at the Olympic Stadium on August 15, 2016 in Rio de Janeiro, Brazil.

Shaunae Miller of the Bahamas runs on her way to winning the gold medal in the Women's 400m Final ahead of silver medalist Allyson Felix of the United States (not pictured) on Day 10 of the Rio 2016 Olympic Games at the Olympic Stadium on August 15, 2016 in Rio de Janeiro, Brazil.

Shaunae Miller of the Bahamas runs on her way to winning the gold medal in the Women's 400m Final ahead of silver medalist Allyson Felix of the United States (not pictured) on Day 10 of the Rio 2016 Olympic Games at the Olympic Stadium on August 15, 2016 in Rio de Janeiro, Brazil.

Allyson Felix of the United States of America competes during the Women's 4 x 400 meter Relay on Day 15 of the Rio 2016 Olympic Games at the Olympic Stadium on August 20, 2016 in Rio de Janeiro, Brazil.

Allyson Felix, six-time Olympic gold medallist in athletics, addressing the 130th IOC Session

BEIJING - AUGUST 21: (L-R) Sherone Simpson of Jamaica, Kerron Stewart of Jamaica, Allyson Felix of the United States and Veronica Campbell-Brown of Jamaica cross the line in the Women's 200m Final held at the National Stadium during Day 13 of the Beijing 2008 Olympic Games on August 21, 2008 in Beijing, China.