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Hear from David Gillick, who trained with a group of athletes in the US, and found it hard to maintain the "intensity" of training levels. Later it would transpire that some of the group were doping and failed drugs tests.

Gillick added: "I used to be on the track watching some of the guys do some seriously amazing stuff in training sessions over 100 and 200 metres, it was phenomenal."

"Maybe I was a little bit naïve at the time but I went over and I was training with some of the fastest athletes in the world. Unfortunately I got injured and it did make me look at some of the other athletes and ask questions about how they were able to sustain that level of training...but I just simply thought that these athletes were better than me."

This clip was taken from 5 live Sport on 8th January 2015.