It takes about 3-4 weeks of regular and challenging exercises to see their muscle bulk build up again.
Other changes you should notice is that the tasks they had difficulty in doing because of weakness should become easier.
This assessment tool is a wonderful way to see if, and how much, your dog is improving.
I would print it out and complete it every month or two and you should see improvements, at least initially.
If your dog isn't improving it may be the exercises aren't hard enough or being done often enough.
If you have any questions let me know
kyliekmarks@gmail.com