In the past couple of weeks, I have gone from doing 1 hour of cardio a day (a mixture of stationary bike, stair stepper and treadmill jogging) to doing mostly running (3 days a week, still on the treadmill for now, slowly building mileage) because I am training for a marathon. I still do crosstraining a couple days a week. Yesterday I noticed a slight pain in my foot - not bad at all, just enough to be annoying, though I don't remember doing anything unusual that made it start. It isn't constant, but just has an occasional pang. The pain is located on the outer edge of my right foot, just in front of the heel (on the other side of the foot from the arch). So far I haven't noticed any action that causes the pain, or makes it worse, except that it usually happens while I am sitting or laying down. I did a pretty easy two-mile run this morning, and had no pain at all while I was running. So my question is, does this sound like an injury of some type, or just normal soreness from increased running? I'm afraid I might be being a bit paranoid, but I don't want to make a minor issue a major one and destroy my training by having to take a lot of time off. The next two days are pretty easy days on my schedule (strength training and cross-training), so maybe I should just see how it feels by Sunday when my long run is scheduled?

Take a break and see how it feels.

Sounds to me like you *could* be developing plantar fasciitis. http://www.aafp.org/afp/20010201/467.html for how to treat it. And it's not just heel pain. It's pain all over the foot, from the arches to the sides, all the way up to the ball of the foot.