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The head of world athletics, Lamine Diack, has admitted the sport faces "a crisis" over allegations of doping by Russian competitors.

In December, a German TV documentary claimed Russian officials systematically accepted payment from athletes to supply banned substances and cover up tests.

To discuss the implications of these doping allegations, Lee James was joined by Olympic gold medallist Jason Gardener, but first, in his first broadcast interview since the allegations were made public, Diack said he was "shocked" and "disturbed" when he first heard the claims of widespread doping in his sport.

(Image: Lamine Diack. Credit: Getty Images)