What sort of training does everyone do inbetween marathon training? You all obviously have say 10-15week training plans leading up to a marathon but how much do you need to do to keep a good level of fitness?
You're going to get a wide range of answers to the first question I'm sure. Some people here don't appear to have any concept of 'inbetween marathon training'
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I'm with James on this one - I really couldn't bear dropping below a certain fitness level. As a result I will be keeping my run frequency about the same but decreasing volume. I did the TR24 last year which is a team event at the end of July. I found that a good target to aim for in the months following the spring marathon. I then have an autumn marathon lined up so I don't slack over the summer, then it all repeats again 
As for how much you *need* to do to maintain fitness, I guess that depends on the individual and what level you want to maintain. I reckon 3 runs a week would be fine on average with one speed and one longer slow run (though not as long as the latter runs of marathon training).
James - what happened on the 17 miler? Was it bad from start to finish? You mentioned electrolytes, did you dehydrate? I agree with Eggy, it's not such a bad thing to have a bad run if you can learn something from it. If they all become bad runs then something is not right though.