He was not able to get up without assistance. He got a referral to PT and began exercises for balance and strength. Of course he is in pain using new muscles. Now he doesn’t want to do them. I have heard folks say not to force feed if your loved one doesn’t want to eat. What about forcing him to exercise?
I found myself doing the exercises with my mother when the PT/OT was at the house. I was trying to encourage her but also it kind of felt like an appointment we all had to keep, less chance that she would give up. I would never force her to do anything but I tried to make it as attractive as possible. I let her know it was something she could do to help us help her. Maybe your spouse could understand that and keep going? It's hard to say, especially with the chronically stubborn, lol!
Now, I can’t convince my mom (age 81) to do even the easiest exercises for more than a day or two. She doesn’t have dementia but is severely deconditioned and uses a walker and refuses to go to the doctor for any reason or to allow physical therapists visit her in her house. She can’t get herself up off the floor when she falls. It’s increasingly hard for her to do laundry, get dishes out of the dishwasher, or use the microwave. I have pointed out that if she loses much more strength or mobility, she won’t be able to live alone and I’m not going to live with her. But it’s still not motivating.
You can encourage him. You can point out what will happen if he does not get stronger; he will need to use a walker, and/or a wheelchair, that is, if he can get in and out of the wheelchair. I assume you don't have the strength to get him up. You may be strong enough to help him with transfers (that is, getting in and out of bed, and in and out of a wheelchair, recliner, etc.) for now. If or when that changes, he will need to live in a skilled nursing facility.
How about setting aside a time of day and doing the exercises with him? Would he do that? He should tell the PT that he is having difficulty and the exercises are painful. He can ask if there is a modified exercise he can do until he builds up a little more strength. Like when you watch exercise videos, there's a high, medium and low level version for people at different levels of ability.
Dementia robs people of their reason, logic and judgment so they literally can't be argued into doing "what's best" for them. Their impaired memory will cause you to re-argue with him every day. Do some more online research and see what Physical Therapists who work with seniors do to increase participation.
It's a no win situation any way you look at it.
When my late husband who had vascular dementia became bedridden, part of me was actually glad as I didn't have to worry about him falling anymore, as he was falling a lot. That may sound mean of me to say, but it gave me one less thing I had to worry about while caring for him.