The
ALS Clinic at the University of Minnesota told my mom (a year and a half ago when she still had some use of her limbs) that she shouldn't do any strength training. She was instructed to do range of motion exercises. Now, I do those exercises for her so that she doesn't get stiff. The OT talked about how very important it was to keep doing the exercises because it's tough to get the motion back once it's lost.
Now I "take my mom for a walk" by walking her legs from her power chair. She's always suffered from restless leg syndrome, so now, as you can imagine, it drives her NUTS. She said anyone who'd like to invent a machine that can "walk" her legs for her from her chair, she'd be happy to test it out!