Why do muscles shrink? There must be a reason. First, we must find the reason, and then we can prescribe the right medicine.

Generally speaking, you should keep proper exercise, give him more massage and give him nutritious food, preferably dog food.

Besides, why not go to the hospital? Do you distrust the hospital, or do you feel that you don't want to spend money on raising a dog? You can find a reputable local hospital to take a look at, at least to diagnose what the cause is.