My shins (specifically the Tibialis Anterior muscle - http://en.wikipedia.org/wiki/File:Tibialis_anterior_2.png) often tighten up while I'm running.
This has happened my whole life when running longer (e.g. more than a mile or so) distances at slower speeds. I was a sprinter years ago in high school (with no problems), but even then if we'd go for longer jog, the outside of my legs below the knee (left leg in particular) would get very tight. Not extremely painful, but uncomfortable - and at its worst, movement of my ankle was impaired.
I started running again (distance only) about a year and half ago, and it kept happening. I did stretch, but that didn't help too much, and I read that I should write out the alphabet with my toes before running. I do that every time I run now, and it definitely helps, but my shin still tightens up, but it really varies (sometimes it's barely noticeable, sometimes much worse).
It's never been bad enough that I have to stop running, but it isn't pleasant and I'm slightly worried that I'm altering my form a little and that it could lead to an injury.
Is there anything else I can do?