So I've been doing a lot of cardio lately, and my calf and lower portion of my leg (below the knee) has been getting really, really tight. It's painful. It never used to do this and I used to be somewhat of a runner (2-3 miles a night about 4 nights a week). I recently switched to a new shoe that is actually a little bit too big for me. Could this be the case? I guess for now, should I switch to lower impact cardio like the exercise bike / elleptical? Please help.