Whilst surfing the internet I came across Richard Irvine-Brown who is a BBC journalist.

He is running the marathon this year in London and has been blogging his progress on the BBC website.

It is quite interesting stuff.  He has been doing it as an experiment - trying out different kinds of training on different weeks, with varying degrees of success.

One week he devoted entirely to fartlek training (including taking advice from Momentum Sports in the article), but because he did it every day he found his legs were in pieces by the end.

Have a look, it makes an interesting read.  The page about him is below - go to the bottom for his list of articles.

http://www.bbc.co.uk/dna/606/U7774651