It’s a bugger, physios use the term ‘core’ without ever explaining what this means and what a strong core helps with. Physiotherapists were saying to me for years, ‘your core is weak’. I didn’t understand what it meant and what effect this could have. Then I had major problems with a disastrous relapse on top of foot drop. I discovered what the core was and it was a bit too late. I tried and tried to make it stronger but to no avail.
Your core is your abdominals, yes, but it’s the whole of your central region, pelvic muscles, back, bottom, everything in the middle essentially.
And you need all of this to be as strong as you can get it, because without a strong core, it’s hard to make the rest of you work. Standing, walking, picking up your feet, turning, sitting. Everything uses the core.
So, the answer is, while you can, exercise that core. Get support from physiotherapists for specific exercises and ways of improving what you have. As Whammel said, look at the info on the MS Trust website.