Since the turn of the millennium, no team has been as dominant in a women's event as the United States has in the 4x400m relay.
Quartets from the North American juggernaut haven't lost the event since 2000, a streak that's expected to remain intact when the gun sounds for the championships' penultimate race on Sunday (15).
The reigning champions come armed with a relay pool that includes three of the year's 11 quickest 400m runners on the flat: Symone Mason, Taylor Manson and Arria Minor, who've clocked 51.32, 51.53 and 51.74 personal bests this year. Mason, a finalist at the 2015 World Youth Championships in Cali, has international experience under her belt, too.
Challengers to the throne?
Powered by two of the five fastest entrants in the 400m hurdles – Shiann Salmon and Sanique Walker – Jamaica seems to be the likeliest candidate, and will be looking to finish on the podium for the second straight championships.
Led by Zeney van der Walt, one of the 400m hurdles favourites, South Africa is expected to be a medal threat as well. So is Australia, who last won a medal in this event in 2008. Germany too is gunning to return to the podium after missing out by 0.38 two years ago in Bydgoszcz.
Others gunning for spots in the final include Sri Lanka, India, Poland and Brazil.
The Indian team includes Hima Das, at 51.13, the fastest 400m runner expected in Tampere, while Tiffani Beatriz Domingos Silva, a sub-53-second runner this season, heads the Brazilian squad.
Bob Ramsak for the IAAF