I did manage to walk the 2.8 miles around Green Lake yesterday, though it took me about 20 minutes longer than usual. I stopped to stretch often. I don't think I did myself any harm at all, and it was certainly fine to be out in the open air.
Now that I know about the psoas muscle and its tendency to tighten, I'm able to keep myself a good deal more comfortable with the right stretching exercises. There's an excellent website called thestretchinginstitute.org.