Mo Farah is prepared to turn his back on track domination and gear up for a marathon struggle as he insists his desire for success is not yet sated.

The 33-year-old completed an Olympic long-distance 'double double' in Rio on Saturday night by storming away to 5,000 metres gold, a week after retaining his 10,000m crown.

Victory made him the first British track and field athlete in history to win four Olympic gold medals.

But he ruled out bidding for further track glory at a third Games in Tokyo in 2020, saying that was a feat for Usain Bolt alone after his sprint 'triple triple'.

Farah is set to bid farewell to the track after next year's World Championships in London, with a view to settling his unfinished business with the marathon.

Explaining his continued hunger for glory, he said: "When I line up I'm in a tunnel, I close out everything.

"All you can see is ahead and not beyond. That's what drives me and why I've become successful and win medals.

"The day you feel you can't see that straight ahead of you, that's when you have to hang up. I'm still in that tunnel and want to continue. At times it's hard and the light turns off sometimes, as you miss your family, you miss your kids, a normal life.

"That's the only thing that really gets me down or makes me think twice about what I do, but it's all worth it."

Grabbing his latest two medals hanging round his neck, he added: "You can't replace it. You have to make the most of the opportunity which is what I've done.

"I want to continue to 2017 on the track and then go on to the road. I won't be away from my family as much. I need to practise and run a couple of key marathons to become successful as for years I've been doing track.

"In 2017 for sure you'll see me on the track. I owe it to the people, the public. I'm going to line up, no matter what, half injured or whatever."

Farah struggled on his only marathon appearance so far, finishing eighth in London in 2014, and knows it will take him time to make his mark on the distance.

"When I did the London Marathon I felt I went straight in the deep end and to be honest I struggled," said Farah, who revealed he could target a race over 26.2 miles in the autumn of 2017. "It was a totally different pain."

The truth is, though, that Farah is showing no signs of slipping on the track. His last lap of his 5,000m was 52.83 seconds, while he revealed he had been running 49secs for 400m in training. Still none of his rivals can live with it.

He explained, however, how the pain of spending long periods away from his young family, wife Tania and four children, had taken its toll. Competing in the marathon would mean less time away from home.

"I do miss my kids six months of the year," said Farah, who has dedicated his two Rio golds to eldest daughter Rhianna and son Hussein. He had dedicated the pair from London 2012 to his twin daughters Aisha and Amani.

"When you see them cry, when you see them not eating as well, being a father and having four kids is not easy and seeing my wife struggle, that's the hard part.

"I'm so looking forward to seeing my son, who's already got his teeth through. I've seen pictures.

"I haven't seen him since I left (home) two months ago. He's growing up fast.

"I miss a lot of time with them. I feel proud and want to spend time with them, give them a hug."