Mo Farah has described taking part in the early stages of this year's London Marathon as "the biggest lesson" of his life.
The double Olympic champion plans to make his debut at the distance at next year's event, but completed just less than half of the course earlier today as part of his training.
The 30-year-old told BBC Sport: "I've learned the biggest lesson of my life. If I had come here next year and made a mess of the race, I don't think I could have dealt with that.
"This year I'll be concentrating on the track. It's hard to do marathon and track racing. I'm here to learn about the course, so that next year I'm ready to go. It's a no-brainer when you think about it.
"The biggest challenge I had was picking up the right drink and I made a mess of that. I'll watch the race back to see how much of a mess I made of it."