Possible piriformis? Got pain from hips shooting down legs used to work out ever then stop after that prolonged sitting...Mri clear

Could be priformis. What your describing could be piriformis syndrome. This is one fo the small muscles of the hip that can compress the sciatic nerve and can cause pain down the leg. It's also possible that it's coming from your back. Can try a course of therapy, and occasionally an injection around the piriformis muscle can help.
Possible. Piriformis syndrome is possible. Most common is a biomechanical causes- look at postural/ergonomic causes. Assuming the MRI is of the ls spine is clear check the hips for possible causes. Also, consider rheumatologic causes which can be checked with bloodwork.