The use of muscle testing is a wonderful neurologic feedback tool. It is quite an art to use correctly since it involves both the tester and the person being tested and variable between both. Recent research theorizes that the brain frequencies actually synchronize when performed correctly (Prof. Frank Bittmann, Universität Potsdam).
Often muscles are considered “weak” or “strong”. This does not mean the general strength of the person, rather if the muscle is performing in a proper manner. An analogy would be a circuit breaker; does the circuit work correctly. Essentially, a muscle that is considered “weak” is in a state where the motor signals to it are reduced. Conversely a muscle might not be relaxing as is should.
The simplest purpose of the muscle test is to determine if it is working properly and when making other challenges does that create a change. Testing isn’t as simple as seeing how strong a muscle is. Position, force application, accomodating body position changes, isolation, timing and many more things are involved in accurately assessing muscle function. Muscles can have imbalance due to injury or from other causes. These imbalances can be due to physical neurological issues, chemical and biochemical issues, and even from emotional and electromagnetic-type issues.