Scott Overall says 'good performances are questioned' in athletics
One of the UK's best runners and medal hopes for next year's Rio Olympics says recent doping scandals have made him "lose faith in athletics".
Scott Overall was the fastest British runner in this year's London Marathon.
Athletics has been hit by claims that athletes are using sophisticated methods to get around tests and the sport has also seen allegations that officials in Russia used banned substances to cover up positive results.
Newsbeat went to meet Scott at his training base in Surrey to talk to him about the issue of doping worldwide.
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