There's a lot of great things to be said about e-stim after stroke. E-stim can be used to do a number of things to help survivors recover. But let me review one: Stretching.
About 30% of the time stroke survivors have "severe" spasticity. How is "severe" defined? Severe is considered "≥ to 3 in the modified Ashworth scale." What does that mean? It means that if you move the joint through its range of motion it is tough to move. The force that used is an outside force; someone other than the survivor moves it (passively).
Severe spasticity in the upper extremity can lead to a fisted hand. In the lower extremity it leads to the foot pointing down at the ankle (plantarflexion).
So how should you stretch spastic muscles? One way is manually. In the ankle is pretty easy. Stand up. This is called a "weigtbearing" stretch. But in the upper extremity... ah, it can be difficult to stretch a fisted hand. It's not just that you're dealing with stretching over all of the joints of the fingers (12 in all). If that you can't fully stretch the fingers without also stretching the wrist. The reason they have to do both gets technical. The muscles that control the fingers, also control the wrist. So to get everything fully stretched you have to extend both the wrist and fingers. "Extend" means that the fingers would be perfectly straight, and the wrist would be pushed back as far as possible.
There was a very influential neuroscientists and Nobel laureate named Sir Charles Sherrington. Sherrington made many discoveries about the nervous system. One of the things that he discovered is that for one set of muscles to contract, the other set of muscles would have to relax. Let's use that hand as an example. For the muscles to open the hand to work properly the muscles that close the hand after relax. Otherwise those muscles would be fighting themselves. Which Sherrington discovered was that in a healthy (non-stroke) situation, when there was an attempt to open the hand the muscles that close the hand would relax. If you want to get technical, it's called reciprocal inhibition.
Trying to stretch the fingers into an open position, while also extending the wrist with a spastic stroke survivor is a bit like herding cats. It's tough to get all of those joints (were up to 13 now) going in the right direction. This is where e-stim can come in.
Because e-stim makes the finger extensors and the wrist extensors fire, it also forces the wrist and finger flexors to relax (reciprocal inhibition). In this case, the electrodes would be put on the back of the forearm with the muscles that open the hand and wrist are. Again, the e-stim would go through the electrodes into the back of the forearm fire the muscles that extend the fingers and wrist. And... at the same time... relax the muscles that close the fingers and wrist.
Talk to your therapist. If you have a lot of spasticity this is something that you can do at home, once trained. The technology tends to be relatively inexpensive, and can be used for an extended period of time. But again, talk to a therapist, and get them to figure out what the right settings and dosage or for you, and then e-stim away!