OP may actually be on to something here. I ran cross country and track in high school, so I was usually running around 5+ miles a day, everyday. During that time, I was 100% fluent. However, as soon as I graduated high school and stopped running, I started stuttering. I wonder if there actually is a correlation between the two? Maybe the endorphins and serotonin we pump into our brain from all that exercise counteracts the overly high-dopamine us stutterers tend to have in our brains? I need to do some more research…