I asked in therapy about the issue I had in mahjong last week https://multipleexperiences.org/2019/01/04/couldnt-hold-myself-up/ with holding up myself up. We discussed the issue with my weakened core muscle. I’ve had multiple sclerosis for almost 21 years and it was my core region that was on of the first things effected by MS that never got better. It an area that has always given me issues and has always been an area we work on in therapy.
A while ago I use to have the same issue when I’d exercise and I couldn’t hold myself up. I tried those back support things that you could by from Amazon but they didn’t help. I found out from my therapist that those aren’t good anyway. Those supports do all the work for you and don’t engage your muscles at all. What ends up happening is your muscles end up weaker because they aren’t working the brace is. I’m better off with a pillow to help engage and lengthen my spine. Hopefully that will help strength the muscles. Of course physical therapy will also add new techniques to my routine to help as well.
I also found an article online that talks about MS and posture and the muscles involved if your interested. https://www.mstrust.org.uk/a-z/understanding-and-improving-your-posture/core-muscles-and-your-posture. This also has various exercises. Then of course there is YouTube that has tons but I choose this one. https://youtu.be/pvGpeh0JRfw
Hope this helps you.