"Its a proven fact that a person backed into a corner, with no way out and fighting for their life, are capable of extraordinary feats of strength - whether it be physical, or in terms of the spiritual. That feeling is the essence of the Inner Pulse, as it allows one to experience a brief moment of maximum spiritual output in order to ensure their continued survival. Everyone can muster the will to use it, though few rarely master it.
The Inner Pulse (ないてきみゃく, Naiteki Myaku) is the name that denotes the act of bringing forth ones maximum spiritual output, usually in a situation that could either mean life or death for the user, in order to ensure the users continued survival and existence. The term was first coined by Naibu Shizuka, though the concept has existed long before it was named.
Everyone has a level of spiritual energy, a reservoir of sorts, that usually cannot be accessed normally. Yoruichi Shihōin explains this as a person's dormant - or latent - spiritual energy, which can slowly be brought forth through fierce battles and harsh training. However, through particularly harsh battles or training in which ones very existence is threatened, bringing forth the energy which is usually locked away until needed can be accessed with greater ease; essentially allowing one to reach the pinnacle of their power. However, there are dangers associated with this usage of the Inner Pulse. If one attempts to bring forth more power than they can safely wield or are not used to handling, they will essentially burn the spiritual power out of themselves and revert to being a mere human.
Emotion also plays an important role in the use of the Inner Pulse, particularly powerful feelings such as love, determination or even fear. This is shown multiple times by both Riki Nagakura and Jinta Kanō, whose emotions are directly linked to their respective spiritual output, ferocity and general feel.
In a life or death situation, or through severe training, the user gains an explosive boost to their base skills for the briefest of moments, allowing for a last-ditched effort to survive and defeat the source of said threat on the users life. Use is usually followed with immediate loss of consciousness and hospitalization in order for the body to heal naturally.
Behind the Scenes Edit
This concept was inspired by conversations between Yoruichi Shihōin and Fujimaru Kudo in the Bleach: The 3rd Phantom game. She explains that only by experiencing one near-death experience after the other, can one actually bring forth their maximum spiritual output at will.