Professional cyclists could still be using methods, similar to those used by Lance Armstrong, to avoid testing positive during anti-doping tests, according to the full report from the Operación Ilex investigation.
Armstrong notoriously managed to avoid testing positive during his career despite using performance enhancing drugs, including EPO, during his seven Tour de France victories. During the heights of his career he remained defiant and insisted he was clean due to never returning a positive test result.
