Martial arts and Zen have a long interwoven history. The most recent changes occurred during the Edo period of Japan (1607-1867). During this period, Japan essentially closed its doors to the outside. Its only contacts to the outside world were indirectly through Okinawa to China, and with the Dutch, who were allowed to enter the port of Nagasaki for limited trade. Foreigners were not allowed to be seen in public. This interval of peace was equivalent to the European Renaissance and followed many years of military struggle and political upheaval. At this point in time, warriors were left without a significant military reason for their existence, and turned inward in self-examination. This resulted in many jutsu ("skills" or "arts") becoming elevated to do forms by their use in facilitating the self-improvement or enlightenment of their practitioners. Zen had much to offer this process, as it long been involved in exploring internal states. Many of today's "external" Japanese martial arts derived from "hard" bujutsu such as judo, kendo, karate-do and Aikido, stress the internal development of the individual as well as the physical, and in many ways are unsuited to their original purpose of warfare. The mainland Chinese martial arts forms have also evolved, in that they also may be divided into "hard, external" vs. "soft, internal" forms. The following describes some of the internal states experienced by martial artists.

Mittsu no kokoro
"The three minds" of karate - these are zenshin ("preparatory mind"), tsushin ("concentrating mind") and zanshin ("remaining mind"). There are additional states which are described or alluded to in various Zen and budo texts.

Zenshin
"Preparatory mind" - this refers to the concept of shin-gi-tai (mind, technique, body), where the body is physically conditioned through exercise and diet, technical strength is gained in the art's techniques by constant practice, and mental strength and confidence are developed.

Tsushin
"Concentrating mind" - this refers to the concept of ten-chi-jin (atmosphere or spiritual aspects, territory or environmental forces, human forces, technique or strategy), where awareness of the immediate surroundings and environment, including the interactions between people and their environment is developed.

Zanshin (kan-ken futatsu no koto or tsuki no kokoro)
Literally "remaining mind/heart" or "reflecting heart or mind", also, "mind like the moon." A state of complete, balanced, continuous and relaxed readiness, awareness and alertness, where you are "present in the moment." Even after a martial arts technique has been completed, you should remain in a balanced and aware state, maintaining correct posture and balance as well as maintaining surveillance over your surroundings at all times. This is often described as "perceiving with both the eyes and the intuitive mind." Zanshin thus connotes "following through" in a technique, as well as preservation of your awareness (remaining on guard) so that you are prepared to respond strategically to what is going on around you, whether to renewed attacks by the same opponent, or for an attack from another direction by a new attacker. The same mindset is preserved at all phases of technique application, whether beginning, continuing or completing a technique.

Zanshin also relates to your awareness of your position within your environment, and to the world around you. You notice the people around you (their body language, expression, voices) because you need to be prepared to interact with them socially, politically, economically and spiritually.

Teishin
"Stopping mind", "confused mind", - when there is an object of thought in the mind, discrimination and thoughts arise, and you are unable to perceive or act without bias.

Shoshin or Nyunan shin
"Soft hearted", "beginner's mind", "spirit of the beginner" - the willingness or ability to receive knowledge, by training with a mind that is free from unfounded bias. In one sense, no attack is ever the same, so that no application of technique is ever the same. Locking in a pre-set pattern of response results in a corresponding loss of adaptability and may deprive you of the opportunity to learn new principles of movement. The underlying principles upon which the technique is based must be understood before you can judge "right" or "wrong" technique.

Mushin or munen mushin
Literally, "no mind", "an empty or clear mind" - a mind not fixed on anything and open to everything, that allows freedom and flexibility to react and adapt to a given situation spontaneously and without conscious thought. Although spontaneity is a feature of mushin, it is not straightforwardly identical with it. It might be said that when in a state of mushin, you are free to use concepts and distinctions without being used by them.

Heijoshin
"Abiding peace of mind", "ordinary mind" - state of spiritual calm during combat, akin to the state of mind when performing ordinary tasks. Cognitive equanimity. One goal of training in martial arts is the cultivation of a mind which is able to meet various types of adversity without becoming perturbed. A mind which is not easily flustered is a mind which will facilitate effective response to physical or psychological threats.

Fudoshin (fudo no seishin or mizu no kokoro)
"Immovable mind", "immovable spirit" or "mind like water", a state in which you are not moved or influenced by external forces; a state of mental equanimity or imperturbability, even when facing an emergency or an adversary. The mind, in this state, is calm and undistracted (metaphorically, therefore, "immovable"). The calm mind, like still water, accurately reflects all that comes before it.
Fudomyo is a Buddhist guardian deity who carries a sword in one hand (to destroy enemies of the Buddhist doctrine), and a rope in the other (to rescue sentient beings from the pit of delusion, or from Buddhist hell-states). He therefore embodies the two-fold Buddhist ideal of wisdom (the sword) and compassion (the rope). To cultivate fudo shin is thus to cultivate a mind which can accommodate itself to changing circumstances without compromise of principles.