Shine Marathon London 2012

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Are there any other foolish souls who have signed up for the Cancer Research Shine marathon walk in London at the end of September.
I'd be keen to understand your training and how it's going.
I'm using it as motivation to shed 75 pounds (14 down, 61 to go).
I've got up to 10 miles continous and 15 miles total in a day.
Would be great to hear from others doing it.