
Gil Roberts of the United States competes during the men's 400m race final at the IAAF World Challenge Meetings in Zagreb, Croatia, on Aug. 29, 2017. (Xinhua/Goran Stanzl)

Gil Roberts of the United States competes during the men's 400m race final at the IAAF World Challenge Meetings in Zagreb, Croatia, on Aug. 29, 2017. (Xinhua/Goran Stanzl)