Olympic champion Dalilah Muhammad smashed one of athletics' oldest world records when she stormed to the women's 400 metres hurdles title in 52.20 seconds at the United States championships in Iowa on Sunday. The blistering run shaved more than a tenth of a second from the previous mark of 52.34 seconds set by Russian Yuliya Pechonkina in 2003. "I'm just shocked," said the 29-year-old Muhammad, who suffered a concussion after ...