I guarantee you, as an experienced instructor, whatever concept you are having a hard time comprehending, especially muscle movement, only works when it shortens. That is one of the hardest concepts in massage school, in my opinion (that and directional concepts). Anyway, whatever you do not understand, at least half of your other classmates are struggling with the same concept or day's lesson. Don't be afraid to ask questions. It is the fear of public speaking that takes hold and prevents most students from asking questions.
Instructors love questions because it helps them understand how to present the material for all learners. All students learn differently, but one thing they have in common is the fear of asking questions. If you think of asking a question with the attitude that questions actually show your level of intelligence and not your stupidity, maybe you would ask more questions. Remember the old adage: There are no stupid questions. When you think about it, how dumb is it to have the instructor right in front of you and not ask a question about the subject matter you do not understand? Why would you rather sit there and pretend you understand a concept when you really haven't a clue at this point? Is it any wonder why you are scoring poorly, which may affect your future career opportunities? Studying and asking questions are important steps to your future success.
Of course, on the flip side, there will always be that student in class who asks a million questions; however, now you know the secret of why she scores so well on her exams even though it may seem a bit annoying in class. What is your fear about asking a question?