Good process, clean sketches and prototyping and attractive hero and money shots. Great work.
Two things I’m going to pick at are:
Can you back this up visually with research, be it yours or from another study?
You’ve identified this as the primary problem statement. I think, given the heavy focus on usability for such a product, that you would benefit from tweaking this statement to reflect on the ergonomic and functional problems/solutions first (answering calls, modularity etc.), and follow this up with the secondary problem, which is making it look good to motivate your target persona during rehab (which as above, can hopefully be backed by research).