This happens usually in one foot, sometimes both. It seems to be a fairly small area of soreness right in the middle of the heel bone on the bottom of the foot.

A few clues: I have decent, not great, running shoes, but this did not happen when the shoes were new (they're still in pretty good condition) nor when I used lower quality shoes previously. So it doesn't seem to be related to the shoes but I could be wrong.

As for running, I never go very far or fast. The most I do, and that rarely, is five miles in 45 minutes, or two miles in 15 minutes. So I'm not hammering and I rarely run more than ten miles in a week, so it doesn't seem like some kind of stress injury. But again, could be wrong.

Don't know much about foot anatomy, is there maybe a tendon that attaches at that point, that I should be trying to stretch a little before running?

Any ideas you tri-monsters have are probably better than any of mine at this point. Thanks for your help.