Going off what I'm reading here only, that typically: Inclusion body myositis (IBM) is a progressive muscle disorder characterized by muscle inflammation, weakness, and atrophy (wasting). It is a type of inflammatory myopathy. The most common symptoms include progressive weakness of the legs, arms, fingers, and wrists.

However, with Frampton, he can still play guitar, so his hands are not effected. Well, the muscles of the hands, extrinsic: the finger flexors and finger extensors, as well as the intrinsic; abductors and adductors of the fingers still work. So in Frampton, his auto immune disease doesn't effect him distal to the elbow.

So whatever, his forearms have, as well as his hands, so should his body, to be immune from the auto immune disease.

I wonder if distal to his knees are equally functional comparable to distal to his elbows? Many times, the body is symmetric in that way.