Board Thread:Naruto Discussions/@comment-6975341-20170913230750

I've been looking around and I couldn't for the life of me pin down an actual description for it. So here is one I made based on information from the anime/manga.

I think that it should be an actual page.

Life Force (生命力, "Inochiryoku") is the very essence of a person and is separate from the soul but is sometimes called one's "energy." It does not carry memories or experiences and for the most part cannot be controlled.

Overview
One's life force determines their lifespan, chakra reserves and overall vitality. The more one has, the longer they live and the slower they age. Life force is ordinarily not visible to the unaided eye unless it is highly concentrated or manifested in large amounts. If a person has a muscular life force their chakra becomes more potent and large and their ability to withstand exhaustion and powerful attacks without succumbing increase.

Injuries that are generally fatal may still kill but do not as quickly一it is possible to lose a limb or even be bisected and still survive or even function normally. These traits are strong enough to survive the removal of tailed beasts, although they are still left severely weakened afterwards and will inevitably die.

Spiritual Energy and Yin Release
Although oftentimes confused with spiritual energy and Yin Release, life force is entirely different. Spiritual Energy (精神エネルギー, "Seishin Enerugī", English TV; "Mental Energy") is the mind's consciousness and can be increased through studying, meditation, and experience. One cannot normally enhance their life force, in any capacity. Yin Release (陰遁, "Inton", English TV; "Dark Style or Shadow Style") is a nature transformation that is based on spiritual energy. It is created by making a higher ratio of spiritual energy in one's chakra when molding it as opposed to physical energy.

Still, the larger one's life force, the stronger their spiritual energy and Yin Release can potentially be.

Trivia

 * The anime and manga never truly expanded on life force. Based on deduction and a bit of research, this is the conclusion on life force's definition that is canon.
 * The Uzumaki clan is known for their strong life force which gives them their famous power.
 * Tsunade, a descendent of the Uzumaki, was able to survive being bisected likely due to the vitality of the Uzumaki. 