Yep I can refer you to an exercise that you can do daily to improve your speech and reduce speech blocks: https://youtu.be/wAybuEe446E?feature=shared Research articles are the description of the video and you can find more on google by searching up "metronome timed training for stuttering". All you need is a metronome app on your phone or YouTube and some text to read from like a book or google "harvard sentences" and use those. Also you need to do the exercise for at least 15 mins a day for 5 days a week for 2 months to expect results to start showing. I recently was participating in tdcs research study where I was required to do this type of exercise. They had me going up to 190 bpm. I guess the upper limit for the bpm is 190 bpm. There's no lower limit. Be sure to immediately decrease the bpm if you start blocking on words or it's a stuggle to keep up. All the best!