In the current Runners World there is a half page on mental tricks; the first of which is to imagine being pulled along by a piece of string attached to the navel. I think this is a great idea as long as you ditch the string and the pulling (I could never see myself as Spiderman). All that is left is the thought of the navel but this, or rather about two finger widths below it, is what you should be thinking of, or rather thinking through. It is your centre of gravity; the core and you can imagine your energy being focused there.
This might sound more fanciful than Spiderman but it is not; it is simple and something I learnt about on a public speaking course. It is an amazingly effective way of giving yourself more presence in front of your audience. You stand evenly balanced on both feet and you think through this area and you feel more firmly rooted and stronger. This can be proved by a simple test. Ask someone to stand upright and then push one of their shoulders; typically it will give way in a fairly floppy fashion. Now tell them to stand upright and think through their centre of gravity. You will now find there is resistance and strength when you push the shoulder.
When you are running this thought locus helps with your sense of balance and posture and it will feel strong long after your leg muscles have tired. This might even help you keep going. (Well perhaps).