Muscle testing is also referred to as Applied Kinesiology. Chiropractors use it to find which parts of the body need adjustment, and to check if an adjustment has been successfully made. They use it combined with elaborate knowledge of the skeletal and musculatory system. If one touches certain key points of the body and at the same time tests if a certain muscle is weak or strong, that can indicate if that key point needs correction or not.
The interesting thing is that muscle testing works just as well on mental or emotional issues as on physical body parts. Basically one can put one's attention on something and then test for a weak or strong response. That is something we can use.
See, the body is not as much of a liar as the conscious mind is. It is much more likely to give an honest assessment of what is going on than the person's analytical thinking is. The body will give answers to things that are submerged and unknown to the conscious processes, and it will give answers without being biased by wishful thinking or social maneuvering.
Many different muscles could be used for the test. The easiest is usually to use the big deltoid muscles or the arms. The client stretches one arm straight out in front of her, or straight out to the side. The facilitator instructs her to resist and then presses down on the arm. And she notices if the arm holds up to being pressed down, or if it gives in and becomes weak. There is a certain knack to sensing it, but once one has got it, it is a very finite sign.
One would pick a muscle that tests strong when we don't put attention on anything in particular. Then we will know that it means something when it tests weak when we bring up particular subjects.
There are much more elaborate systems of using and interpreting muscle testing. Different muscles seem to correspond to different organs along the lines of the meridians. If you want to study and use that, that could be useful, but it is beyond the scope of what we get into here. We simply find a muscle that is usually strong and we agree with the person that it will be our test. This agreement becomes to governing factor.
Basically, strong means "Yes" and weak means "No". Whether a Yes or a No answer is most desirable depends on what we ask for, but most often we will ask in such a way that a strong response is good. As in "Do you feel good about yourself" - Test - should be strong, meaning "Yes". If it is weak, we could then work on the issue of feeling good about oneself, with our usual processing techniques. And then, when we appear to have gotten somewhere, we could do a muscle test again to confirm it. If it is now strong when we ask the same question, then we have probably done a good job.
Muscle testing is a very finite way of testing. If nothing else, it appears very finite to the client. It provides a very tangible and convincing "proof" to the client that we have actually gotten a result. The client can much more easily invalidate purely mental and emotional results. Even if she feels good and she has found out something new, she might still convince herself a few days later that it was "just" something she imagined. But if we have tested it and we both realized that what used to be weak is now strong, that might weigh a lot more heavily in the favor of accepting the change that took place.
The muscles really do react to what one thinks and feels and imagines. But the test it fairly honest and unbiased. Whereas a purely analytical assessment of what one feels might not be as honest.
The facilitator can use muscle testing according to preference. It is just one of the tools that are available. You don't have to use it for anything at all, or you can use it for every single issue that you work on with the client, that is up to you.
If you do a number of tests after one another the arm will eventually become tired. One can then switch over to the other arm, or take a rest for a moment.
Muscle testing can be used for a comprehensive test of items from a list or arrived at some other systematic way.
For example, you can read aloud, or let the client read from a list of possible items one could be allergic to, and you can test her arm for each one. This can give amazingly precise results.
Also, one can go over the client's body and test each body part systematically. It can be done by mentioning it and having her put attention on it, or if it is an outer body part it can be touched lightly. And you test for each one if it is strong or weak. This indicates areas that should be worked on in one way or another.
A transformational process facilitator is not a health practitioner, so don't pretend that you are. If the person needs medical attention, refer her to an appropriate practitioner. What you are addressing is the mental, emotional, and spiritual phenomena that can be found in the person's world. Finding out what is there and changing it can have profound effects, also on health, but you aren't going to promise that.
In using muscle testing, it is important that you are very precise in what you ask for or what you put attention on. If you give a sloppy unfocused question or direction you will get a confused answer.
There are many texts available on muscle testing that can give you a much more thorough understanding of its use than what is presented here.