This is a question that cannot be answered without further investigation or information, and it is not the expected course of Parkinson’s disease that an arm is not functioning properly, and neither force nor feeling should be affected by Parkinson’s disease.
You need to investigate if there is any constriction of the nerve fibers in the cervical vertebrae — it can cause feeling worse and the effect of force — without any pain. You need to have a clinical examination and possibly a complementary X-ray, and you can do that very well at the health center.
♪ The Hook of Widner ♪