I've recently started to focus on increasing my mileage so I have a solid base to start a marathon programme in January. I'm a sub-19 5k, sub-40 10k runner at present but improving all the time. I've started doing a weekly interval session with a club at my local track which I'm really enjoying and seeing results from. I realise the step up from shorter distances to 26.2 is a big one (aiming for sub3hr) which is why I'm focussing my efforts on aerobic pace running and working my way up to a 40mile week before I start the marathon training. schedule. I guess my question really is, will the interval work hinder my progress building an aerobic base? I've read a little on periodisation and a little on the Lydiard approach (old school I know) and they all seem to say build a base before the speed work, but I'm already doing the speed work. Does that mean my base is already sufficient to continue speed work or is it going to be detrimental to my marathon training?