This is a means of physical culture that has fallen by the wayside over the years, much like hand balancing. Muscle control involves flexing and relaxing the muscles individually and in groups.
By practicing these moves you not only gain a stronger command of the muscles but will be able to make them dance. Many old time strongmen like Maxick and Otto Arco (shown below) had muscle control in their acts. They would move from position to position showing off their muscles and the control they had over them.
The basic book was, and still is, Muscle Control by Maxick.
This practice also increase your mind-muscle connection. And that means on thing: you become stronger.
Their are tons of different moves for every muscle in the body. Though Maxick and some others promoted muscle control as the end-all be-all of strength, I think its better to add in to your other training. Definitely muscle control is different from other methods and you should gain the benefits by giving it some practice. Of course, as the next picture shows, isolating abdominal tendons, you can take this art pretty far.
Here is a video showing off some abdominal muscle control. The first two moves, flexing and the vacuum, can be done by most anyone and certainly after a little practice. The second two, the rope and belly dancing, may take a little more.
I’ve done quite a bit of muscle control over the years. So much so that I put together a course. In fact its the first of its kind, showing muscle control exercises on video as well as sharing virtually all books written by the oldtime masters of this art. Check out the Master Muscle Control Course here.
For even more check out this article All About Muscle Control.