Mo Farah believes this year's London Marathon will prove tougher than the Olympics.
The 30-year-old, who claimed double gold in 5,000 and 10,000m in the 2012 Games, is preparing for his first ever marathon at the famous event in April.
Farah has been training in the Rift Valley in Kenya and has increased his already intense schedule from the routine he used in the run-up to the Olympics.
He told the Guardian: "It's hard but I have to do it. It's London. I could easily sit back and say I'm going to stay at home and train but I need to come out here to give it 110 per cent because I've never seen a stronger marathon field, from the world record holder to guys who are running two hours five, two hours four consistently.
"It's going to be a lot harder than my Olympics or world championship races."