Experts split on cause of Contador's Tour de France doping positive

Alberto Contador during his press conference as he tries to explain how his urine sample became contaminated with clenbuterol

Alberto Contador during his press conference as he tries to explain how his urine sample became contaminated with clenbuterol (Image credit: AFP)

Tour de France winner Alberto Contador vigorously defended himself today after announcing that he had tested positive for the banned drug Clenbuterol during the Tour's second rest day.