No! The goal is to feel a good stretch to increase your range of motion if it is limited by tight muscles. The normal range of motion is 40 to 60 mm so if you are in the lower end of normal, you should be able to use the medium size within a couple of steps of the end since the range of the medium size is 33 mm to 43 mm. The large ranges from 44 mm to 54 mm but some people will never be able to open wide enough to use the large gentle jaw and some will. Those that are able to use the large might feel that the lower steps are sufficient and others might be able to stretch more. The key is to not overstretch.