Hi Lauren_April
As research is a generative process there is virtually always more research that is useful in just about any area of inquiry. There is no such thing as an over-researched area. Good research results always produces all sorts of new and interesting questions that we need to know more about. And then there is the scientific principle of replication. Studies should be replicated in different localities with different populations. so repeating answers to questions is an essential part of scientific inquiry.
At your level you will be contributing something that is meaningful but it is quite limited and you should be thinking about something that is quite contained. One thing to consider is the research interests of your superivsor(s) as they may have one piece of a larger research questions that they want answering. For example conducting a clinical trial would be way too ambitious. Projects that can be quite contained could be examining a single measurement property of an outcome measure in a different population. Or a small qualitative study examining the experiences of patients of an aspect of physiotherapy. A case study of a novel treatment could be another. A survey of physios, or patients about some aspect of physiotherapy can also be quite contained. Of course this all depends on the requirements of your school. Getting ethics approval can be quite a mission so for a student project you may want to consider something that doesn't involve patients - usually getting ethics approval from a university committee (not involving patients but say involving healthy students) is less difficult than getting approval from health and disability ethics committees.
This might sound contradictory to what I just said about aligning your project with that of your supervisors. However it is important that you can get passionate about your topic. Choose something that you can really get interested in. You will be putting a lot of time into it and if it is something you are really interested in this will sustain you during the difficult times.
So think about areas that really interest you so far. And try to engage your supervisor. What has really interested you about physiotherapy so far?