We're at the Diamond League athletics meeting in Birmingham to talk to two reigning Olympic champions, Allyson Felix, who won gold at London 2012 in the 200m, 4 x 100m and 4 x 400m relays and triple jump gold medallist Christian Taylor. We also catch up with Australia's Commonwealth discus champion, Dani Samuels, and Commonwealth 400m silver medallist Wayde van Niekerk from South Africa as they share their hopes for the World Championships in Beijing this August.