US’ Tianna Madison, US’ Carmelita Jeter,

Tianna Madison, Carmelita Jeter, Bianca Knight and Allyson Felix celebrate their new world record. (AFP PHOTO / OLIVIER MORIN)

Tianna Madison, Carmelita Jeter, Bianca Knight and Allyson Felix celebrate their new world record. (AFP PHOTO / OLIVIER MORIN)

US’ Tianna Madison, US’ Carmelita Jeter, US’ Bianca Knight and US’ Allyson Felix celebrate after winning the women’s 4 x 100m relay final at the athletics event of the London 2012 Olympic Games on August 10, 2012 in London. AFP PHOTO / OLIVIER MORINOLIVIER MORIN/AFP/GettyImages