I don't think it makes much of a difference to be honest. I do work out and exercise regularly, basically daily and my stutter, while mild at this point, hasn't really shown any significant improvements. However, even if it's psychosomatic, if one thinks it works for them, then please go ahead and do it. A remedy doesn't need to be scientifically proven if nobody is harmed by it. If it works, it works. This is coming from someone who always trusts in the science.