Admittedly I am only getting back into my running groove now but this has been an off an on issue even when I was running regularly and in good shape. I can't pinpoint the problem bc it doesn't happen every time, in fact it usually is fine. I run and other days I do weights (lower weights, high reps a la Body Pump). I wear barefoot running shoes but it was a problem even in my good running shoes. Any thoughts on cause, like technique/ form? I run outside on sidewalks or trails.