Post-op home rehabilitation equipment

Hello Everyone :)

I'm a 4th year industrial design student at the Cape Peninsula University of Technology. I am wanting to design a product, for home or session use, that will assist in the rehabilitation of peoples muscles and joints after an operation.

I know that ther are a number of products out there already, but I would like to focus on an area that has perhaps not really been catered for or improve on an existing piece of equipment. If you have any ideas or information on this topic or who I could speak to or websites I should look at, it would be greatly appretiated.

Thank You

Callum