sinew - ken (Chin)- 腱 (筋)
bone - hone (ku)- 骨
energy - ki (chi)- 精神 (腕力 - physical strength, muscular power, force)
The reason the characters are so important for depending on which is used can provide meaning that may or may not be related to the Japanese word used unless it was adopted by a group, martial art group, where it takes on its unique meaning for that group:
勢力争い（せいりょくあらそい） / a power struggle
体勢（たいせい） / a posture, a stance
態勢（たいせい） / an attitude, preparedness, a condition
勢いよく（いきおいよく） / vigorously, with great force
to my view this creates a situation where it becomes extremely important to discover the actual character's the master's intended for words in English such as "Chin-ku-chi" to discover their true meaning. It should be understood that sometimes characters when adopted by a group, MA, don't necessarily translate because of its unique usage within only that group vs. mainstream kanji/kana as defined by the culture in general.
Take: 全力を注ぐ（ぜんりょくをそそぐ） / focus one's efforts, concentrate one's energies
This kanji, i.e. 注, still falls under the overall word definition of "energy" but it is actually not the one used for this particular word. It does denote a specificity that applies to the general usage of the word in Western Karate, overall and in general when defined. To focus effort and concentrate energy to a single point such as the fore-knuckles of the tate-ken, vertical fist, you have to apply a set of principles, fundamental principles of martial systems, to gain the maximum energy application to the target. This is what is meant when one uses the term, "chin-ku-chi."
Notice the examples just prior to this paragraph above where the principles are alluded too. Posture, stance, attitude, force, etc. Although not inclusive or complete they do lead toward a greater understanding and meaning in the application of chin-ku-chi in our teachings and practices of "Ti or Te."
省エネ（しょうえね） / energy conservation, saving energy
In this above next example the character for energy is, 省, which in itself talks of one small fundamental principle which is the conservation of energy so it might be applied to the target. If body posture and alignment along with other energy conservation principles, i.e. positive relaxation, force direction, etc., conserve energy within the body so when applied it is not dissipated by faulty body alignment where muscles take the energy to maintain its posture thus removing energy traveling to the point of departure, the fist or foot, etc. It is therefore a dangerous and limiting function of English to diminish the intent of the Asian karate master's intent in their teachings because we look to words with specifics vs. a more general feel and philosophy that allows a greater understanding, i.e. getting outside the box we place around our interpretations due to our culture vs. the Asian culture driving the discipline of such as karate, aikido, kung fu, etc.
This next one I kind of like a bit as you will see:
精魂を傾ける（せいこんをかたむける） / put one's whole heart and soul, devote all one's energy, exert one's utmost strength
When I read about "whole heart" and "soul" and "devotion of one's energy" as well as "exert one's UTMOST strength" I feel it speaks to an aspect of energy that the exactness of most definitions to chin-ku-chi misses. The deal of "wholehearted" practice of a martial system. I suspect this is one of many reasons the named chosen for the branch I practice was chosen, i.e. "one heart" style.
The character, 魂, is also used to mean "energy" but in a more metaphysical way by a direct meaning of "a soul, a spirit or a ghost." The statement also includes the other characters that do mean "energy" directly, i.e. 精, and when you derive additional meaning to such characters they do include soul, spirit, heart, etc. which also could and does expand the possibilities of the meaning we have for such terms, words or phrases.