I think I have some experience on this subject.

In my case, the purpose of shackles and other restraints is not to cause disproportionate pain.
Our ideology believes that restraints do not hurt. Pain comes when you cannot adapt to them and thus create situations that produce additional pain.

Of course, there are cases where pain, torture and other sadistic needs are desired. I will not talk about them now.

For me, restraints etc mean certainty and stability that is useless to fight against.
It is about adaptation (and surrender).

The body quickly learns restrictions, even those caused by restraints, especially if they remain constant from day to day.

For example, walking in leg irons is learned relatively quickly, the muscle memory of the legs learns the step length easily and thus the leg irons work as they should: they slow down walking.... they also prevent unnecessary kicking if that is the case.
The most important thing is that they limit movement at all times.

The same thing is basically at hand. There are several possibilities for limiting them.

When thinking about permanent effects, I can mention that for example I have the step length taught by the leg irons also in those rare moments when I am not locked in them.

The same thing goes for my arms. My hands are always in my lap when I sit freely, without handcuffs. I automatically hold them so that they are locked at my waist in front of me.
Of course, my handcuff practices vary, but this is my basic position.

We have also found that it is difficult for me to get up on my own initiative because practically all my movements are controlled, e.g. by the guard's hand grip or by using a leash.

I exercise during the day within the limits of my restraints.
Exercise is important even if it is limited.