However – just how many do you mean by ‘a few’ 20 mile runs in?
I think it depends why you’re doing them and how fast you are. I read in lots of places that the physiological benefits of running up to 2.5 hours are great but after that the recovery period is too long and prevents good training for a few days afterwards. The general rule is that long runs shouldn’t be more than 30% of weekly mileage but that’s hard for low mileage runners.
I’m marathon training at the moment too and I’m planning to do 5 runs of 2.5 hours – I did one last weekend on Ilkley Moor and managed 18miles with 1800′ of ascent – and will do some longer ones on the road sometime soon (ugh).
I’m also planning a 22miler at some point, just once, for the psychological reassurance that I can do the distance.
