Chinkuchi, there are principles involved here. One of the explanations, as seen in a previous posting, for chinkuchi is the locking of joints. The quote, "Chinkuchi is the locking of the joints and tightening of the muscles." In the fundamental principles you have "sequential locking" that explains how joint locks, etc. work on the human body. In that sequential locking there is a reciprocal. We as karate-ka exercise sequential locking for our own techniques and this is one way to help explain chinkuchi.
"A properly aligned punch will take our own joints to a constructively "locked" position, removing enough slack to create the stability required to deliver force." - Steven J. Pearlman, The Book of Martial Power.
It is here that a much fuller explanation of the Okinawan concept of chinkuchi can be found. It does not refute the current explanations from a variety of sources but expands the explanation for a greater understanding. The fundamental principles of martial systems encompass explanations of how all principles properly applied contribute to the essence and explanation of chinkuchi.
This is worth the time and effort to explore. Properly applied sequential locking can be a weakness and yet it is also our strength as explained above. It is the yin-yang of how martial arts are learned, trained and applied in fighting, conflicts and combat. The next time you hear the word chinkuchi in Isshinryu you can find explanations here and further explanations in the study of the fundamental principles of martial systems.
If you so desired you could use both terms or phrases interchangeably, i.e. chinkuchi or principles or chinkuchi or principles of martial systems, etc.