A year ago I ran the Rome marathon, and despite being no newcomer to marathon running and having trained well, or so I thought, I walked quite a bit from about 15 miles on. It was a painful experience and I finished in 4.08.
FLM was the next marathon I ran after that and I didn't walk until about 19 or 20 miles. I so wanted to get in under 4 hours because I hadn't managed to get near my 3.57 PB since I'd done it in 2003. I finished FLM in 4.00.53 totally gutted.
The next marathon was a month later in Halstead but that was a training run for an ultra I was doing in June. I also ran two miles before the start to make it 28.2. Although I finished that marathon in over 4 hours (because I wasn't racing) it was the first time since the '80's that I'd run the whole 26.2...I didn't walk at all, and the confidence that gave me for future marathons is immeasureable because I now
know I can run the whole way.
However, the mind is so powerful and it is ultimately programmed to protect the body, which is why it will insist that you stop running when the pain starts in a marathon. Your mind will also tell you all kinds of things to make you stop running again and again after you've stopped once because your legs and various other muscles and joints are getting damaged each time that you start running again.
So long as there is not a serious injury going on (and you will certainly be aware of that if there is), and you have trained to run a marathon, then there is no reason to stop. So long as you follow a post race recovery plan of rest and correct nutrition your body will repair itself. If you do stop running you must set a time limit or some other kind of limit to the walk break, before you actually stop running.
Last Sunday, I was within a mile and a half of the finish line of the marathon, I was running up a short incline into a strong headwind and it was so tough that my quads began to burn with the exertion...that is not the sort of sensation you need to feel while running a marathon and I knew (from my anatomy and physiology experience in my work) that I needed to give them a short break if I was to finish the marathon in a reasonable condition. So I told myself that I would stop running and walk just long enough for my quads to settle down again, which is what I did. I didn't stop again until the finish because there was no real need and I didn't give myself permission. I also carried on overtaking runners right up to the finish line.
Having a planned run/ walk strategy is another matter entirely.
I entered the Kent 50 Challenge last year. The 'race' is 52.4 miles (double marathon) and I knew I couldn't run the whole way so I planned to run/walk it. The strategy I used was based on 11 min/miling. I ran to the first mile marker and walked to 11 minutes. Obviously by 11 minutes I'd already walked a little way into the 2nd mile. I then ran to the 2nd mile marker and walked until 22 minutes, ran to the 3rd mile marker and walked the remaining time up to 33 minutes, and so on. I did have a list of all my mile times with me so I didn't have to do the mental calculations...which gets harder as you get more tired. But this system worked really well and I didn't start feeling real fatigue until way over 30 miles. The last 10 or so were tough and I did slow, the walk breaks became longer and longer, but I still finished the whole 52.4 in 10 hours 15 minutes. If you're interested you can read about it here:
http://www.runnersworld.co.uk/news/article.asp?UAN=2012&v=1&sp=
I had to do it a few times during my first few years of running in (I think) 4 different ocasions - always half-marathons... I went off too fast...
