Kinesiology ( for healing) uses the fact that a muscle can only handle one stress at a time. Some of the things that stress us are physical (pushing on the arm), a memory (thought), chemical (including food) or an untrue statement.
Kinesiology exploits this fact by using the muscle monitoring technique (physically stressing the body) while introducing one of the above stresses.
If the muscle holds firm, the introduced stress is not a problem.
For a more in depth explanation go here.