Very good question, I have wanted to ask about them myself.
I realised I had to do something as I was in constant pain and getting no sleep.
What has worked for me (within a month).
Was sitting in a chair,locking my leg straight at the knee, tightening the muscle and lifting a weight on my ankle.
It was very hard at first but it is getting easier,a lot of the cramps have gone and I am more stable.
I also put my back against the wall and slide down bending the knees to get more movement/strength etc.
When I have to drive over 30 mins I take my shoes of as it gives me more room,I also use cruise control a lot and use that to change speed (car is auto).
I still get pains but its a bit of a help.
My doctor kept changing my medicine and I thought that was the problem not muscle wastage.