- 5 updates
Jamaican sprinter Usain Bolt has revealed that he has to stay "constantly vigilant" to remain drug free.
Athletics has been blighted by doping scandals in recent months after athletes, including the former 100m world record holder Asafa Powell, tested positive for banned substances.
The multiple Olympic champion says he makes sure he works with people he trusts as ITV News' Paul Davies reports:
The world's fastest man and Manchester United fan Usain Bolt has told ITV News that he is sure David Moyes "heard" his recent Instagram video message in which the sprinter said the Old Trafford boss needed to invest in his midfield.
"I was sitting at home and watching the game (against Liverpool) and I saw that in the midfield is where we are most weakest so I was just voicing my concern.
"I think David Moyes heard, I'm sure, because it was all over the news. I think he surely got that message. He got (Marouane) Fellaini (in) and (Shinji) Kagawa is now playing so the team is much better and a lot more stable."
Six-time Olympic champion Usain Bolt is reconsidering his retirement after the Rio 2016 Olympic Games and says he is likely to compete for a further year after that.
In an interview with Channel 5 News at his autobiography book launch at London's Selfridges store, he said: "I am definitely reconsidering. I think my fans especially have really voiced their concern about me retiring.
"They think I should carry on and so do my sponsors. I have discussed it with my coach and he says it is possible. We will see what happens but it's on the cards that I will extend it by one more year."
Hundreds of fans have queued in London to catch a glimpse of the world's fastest man, Usain Bolt, as he signs copies of his new book 'Faster Than Lightning' in Selfridges.
At the launch of his new autobiography 'Faster Than Lightning' in London, the world's fastest man said: "If you want to be the best, or you want to strive for more, you've got to set goals in life."