Allyson Michelle Felix is a retired American track and field athlete who competed in the 100 meters, 200 meters and 400 meters. She specialized in the 200 meters from 2003 to 2013, then gradually shifted to the 400 meters later in her career. At 200 meters, Felix is the 2012 Olympic champion, a three-time world champion (2005–2009), a two-time Olympic silver medalist, and the 2011 world bronze medalist. At 400 meters, she is the 2015 world champion, 2011 world silver medalist, 2016 Olympic silver medalist, 2017 world bronze medalist, and 2020 Olympic bronze medalist. Across the short distances, Felix is a ten-time U.S. national champion.
Novlene Hilaire Williams-Mills, is a retired Jamaican track and field athlete. She won the bronze medal in the 400 metres at the 2007 World Championships. She is also a three-time Olympic silver medallist in the 4×400 metres relay. In 2015 she won relay gold alongside her Jamaican teammates.
The women's 400 metres competition at the 2012 Summer Olympics took place between 3–5 August at the Olympic Stadium.
The women's 4 × 400 metres relay competition at the 2012 Summer Olympics in London, United Kingdom was held at the Olympic Stadium on 10–11 August.
The Women's 400 metres at the 2011 World Championships in Athletics was held at the Daegu Stadium on August 27, 28 and 29.
The Women's 4 × 400 metres relay event at the 2011 World Championships in Athletics was held at the Daegu Stadium on 2 and 3 September. Friday and Saturday. This is a change in schedule from previous years when all the relays were at the end of the program. This might necessitate a change in strategy to allow for team members involved in other events.
Francena Lynette McCorory is a retired American track and field athlete, known primarily for running the 400 meters. She was the 2011 World bronze medalist in the 400 meters and was a member of the gold medal-winning 2012 and 2016 United States Olympic 4 x 400 m relay teams. She was the IAAF 400 meter Indoor World Champion in 2014. McCorory retired in 2021.
The women's 400 metres at the 2013 World Championships in Athletics was held at the Luzhniki Stadium on 10–12 August.
The women's 4 × 400 metres relay at the 2013 World Championships in Athletics was held at the Luzhniki Stadium on 16–17 August.
The women's 4 × 400 metres relay competition at the 2016 Summer Olympics in Rio de Janeiro, Brazil was held at the Estádio Olímpico João Havelange on 19–20 August.
The women's 400 metres at the 2015 World Championships in Athletics was held at the Beijing National Stadium on 24, 25 and 27 August. Christine Ohuruogu of Great Britain entered the competition as the defending champion.
The women's 4 × 100 metres relay at the 2015 World Championships in Athletics was held at the Beijing National Stadium on 29 August.
The men's 4 × 400 metres relay at the 2015 World Championships in Athletics was held at the Beijing National Stadium on 29 and 30 August.
The men's 4 × 100 metres relay at the 2017 World Championships in Athletics was held at the United kingdom,London Olympic Stadium on 12 August.
The women's 4 × 400 metres relay at the 2017 World Championships in Athletics was held at the London Olympic Stadium on 12–13 August.
The women's 4 × 400 metres relay at the 2018 IAAF World Indoor Championships took place on 3 and 4 March 2018.
The women's 4 × 400 metres relay event at the 2020 Summer Olympics took place on 5 and 7 August 2021 at the Japan National Stadium. There were 16 competing relay teams, with each team having at least 5 members from which 4 were selected in each round.
The mixed 4 × 400 metres relay at the 2019 World Athletics Championships was held at the Khalifa International Stadium in Doha from 28 to 29 September 2019.
The women's 4 × 400 metres relay at the 2019 World Athletics Championships was held at the Khalifa International Stadium in Doha, Qatar, from 5 to 6 October 2019. In the final the Jamaican team were initially disqualified, but were reinstated as the bronze medallists upon appeal.
The women's 4 × 100 metres relay at the 2019 World Athletics Championships was held at the Khalifa International Stadium in Doha, Qatar, from 4 to 5 October 2019.
