Rush was in so much pain that he was only able to play golf three or four times a week.
I believe Rush had indicated that his back problem is in the cervical area behind his larynx. Golf does put a tremendous stress on the back, but it is the lower back, not the area Rush has a problem with. If the pain in the cervical area is controlled by pain meds, I see no reason why Golf should aggrivate the situation.
Playing golf may be evidence that Rush does not need to be confined to a wheel chair. But it is not any kind of evidence that he did not experience episodes of intense chronic pain.
I have some very painful dental problems right now (impacted wisdom teeth). Yet I can do many ordinary things, even eating.