When a muscle changes from one state (balanced or unbalanced) to another (unbalanced or balanced).
This definition is different from what many branches of Kinesiology used to say, especially during the early development of Kinesiology. In the past, they used to say that a Muscle Change was when a Strong Muscle turned it state into a Weak Muscle or a Weak Muscle turned into a Strong Muscle. But this is not correct from a neuromuscular point of view, as Richard D. Utt, L.Ac, founder of Applied Physiology, has outlined.
We should say that a Muscle Change is when a balanced muscle (that is in a homeostatic state or Normotonic Muscle) can change into an unbalanced muscle (that can be either Hypertonic Muscle or Hypotonic Muscle), or when an unbalanced muscle (that can be either Hypertonic Muscle or Hypotonic Muscle), changes into balanced muscle (homeostatic state. Normotonic Muscle).