My question is about both shoes and injuries:
After reading the book "Born to Run" and doing a little bit of research, I decided to try barefoot running. I'm not literally barefoot -- I'm wearing Vibram Fivefingers -- but it feels like I'm running without any shoes on. I've been running in them since late April, and it's been fantastic until now. My steps are lighter, and I'm landing mid-foot instead of on my heel, so there's no jarring impact on my joints. PLUS, I can actually feel my muscles working harder and getting stronger than they ever were in regular running shoes. I even ran a 10K in the Vibrams last month!
HOWEVER, about a week and a half ago I noticed some slight soreness in the top of my left foot. I had just run an easy-paced 1.5 miles and walked up and down a long set of stairs twice when I noticed the discomfort, so I walked the remaining 1.5 miles home. Ever since then, it's been getting worse: I tried to run a couple of miles (in regular running shoes) 4 days ago, and I ended up having to run/walk the second mile. When I tried to go running yesterday night, the discomfort was both immediate and more intense than before as soon as I ran the first few steps.
I had plantar faciitis a few years ago and soaking my feet in warm water helped then, but soaking my foot hasn't had the same effect this time around. The pain is localized in the top-center of my left foot just under my middle toes, and seems to be worst when I try to run (in any kind of shoe) and when I wear flip-flops.
My question is twofold: Does this sound like a muscular injury or a stress fracture? And, is it something the minimalist shoes caused, or something that would've happened regardless of footwear?