When an Indicator Muscle (IM) changes from balanced (in a homeostatic state) to unbalanced (it can be either Hypertonic Muscle or Hypotonic Muscle). Or when the Indicator Muscle (IM) changes from unbalanced (it can be either Hypertonic Muscle or Hypotonic Muscle), to balanced (homeostatic state).
See also Muscle Change and Indicator Muscle (IM).