See Muscle Response Testing (MRT).
George J. Goodheart, Jr, D.C. started by testing the functional integrity of a particular muscle or muscles involved with the shoulder, but kinesiology testing has evolved to use the muscle testing as an indicator of energy changes within the body. For this reason it is sometimes called muscle monitoring, and practitioners will refer to an Indicator Muscle (IM) or a clear circuit muscle indicator (Three in One).
Many practitioners also prefer the term muscle monitoring because testing implies something that the client can pass or fail, and clients can easily jump to the conclusion that a weak muscle response is a failure, rather than simply an indication of a particular state. Some practitioners also talk about muscle feedback for the same reason.