Aiki is a fundamental part of the martial arts of Aikijujutsu and the associated art of Aikido. However from the literature available it is not clear what Aiki is! In the books by Kondo and Davey, the word Aiki is used mainly to refer to the initial actions used to unbalance the opponent without a detailed explanation of why these actions should accomplish this. In books on Aikido, no or very little reference is made to Aiki, creating even more uncertainty. Furthermore, what is also unclear is the difference between these arts and other similar arts such as Jujutsu and Judo.
The publications in Aikijujutsu and Aikido categorise the methods to deal with an attack in terms of the initial form of the attack, for example by pushing/striking, pulling or holding a particular part of the body, and the technique used to finally control the opponent, for example a particular form of arm twist. It is usually stated that it is important to unbalance the opponent initially before trying to control him. From the descriptions given, it is not clear in many cases when the unbalance phase starts or finishes and when the control element starts. The same uncertainty exists for the art of Jujutsu and the associated art of Judo. If Aiki is referring to the initial unbalancing phase of the opponent then there should be a clear difference in this respect between Aikijujutsu/Aikido and Jujutsu/Judo.
In an attempt to clarify the above issues, an investigation was undertaken into the method(s) of unbalancing an opponent used in Aiki related arts. It was hoped that this investigation would provide an understanding of the word Aiki and how Aiki related arts differ from other similar arts.
The investigation took the form of studying the photographic and video information available in the public domain illustrating the techniques of Aikijujutsu, Aikido, Jujutsu and Judo, with particular attention being paid to the initial interaction between Tori and Uke where the act of unbalancing Uke was likely to occur. The information from the archive material was supplemented with a study into how humans maintain and lose balance when pulling or pushing or being pulled or pushed. The investigation took on both a theoretical and experimental nature as theories were developed and then tested out. In this way, possible theories were developed for Aiki and applied to the archive material to see how well they accounted for the actions of Tori and Uke during the unbalancing phase of a large number of techniques. The final interpretation of the term Aiki proposed in this article was developed from this process.
Tori refers to the person who is executing the technique and Uke the person who is receiving the technique and therefore Uke is the one who is restrained or thrown. Consequently, from the point of view of this investigation Uke is the person that is unbalanced by Tori and, for ease, will be referred to in the male gender.
To provide the necessary theoretical description of Aiki it is necessary to understand the influence of forces on the body and its effect on balance.
Influence of Forces on the Centre of Mass
The Centre of Mass (COM) of a body is a point where external forces effectively act to produce linear motion of the body. In addition those external forces whose line of action does not pass through the COM will cause the body to rotate about its COM. The force of gravity, due to the earth, acts at the COM and therefore produces only linear motion of the body towards the centre of the earth. Other forces generally produce both linear and rotational motion of the body. The human body under the control of the mind will always attempt to control the effect of the external forces to prevent unwanted loss of balance and therefore the possibility of injury.
When the human body is not under the action of any external forces then its COM remains at the same point in space as the joints of the body are moved. This means that a body cannot move its COM simply by moving its joints. To move its COM it needs to generate an external force on the body. On earth this is possible by, for example, extending the legs against the ground to create horizontal and vertical motion or pushing against another object with say the hands. By using muscles to extend the legs against the ground an upward force, called the ground reaction force, at the feet is created to balance gravity pulling downwards so that the body does not fall to the ground.
Maintaining Balance when Attacking or Defending
The word balance refers to controlling the forces on the body to prevent unwanted movements. Controlling ones balance is particularly important in preventing the body from falling due to gravity and possibly causing injury on impact with the ground. In this case, balance is retained by keeping the COM within the area of the feet base. Loss of balance means that the body is no longer in control of the forces on the body and therefore is unable to resist the effect of them, which makes it easy to control someone who has lost their balance.
In both attack and defence the body is subjected to an applied force from another body at the contact point. This is called the Contact Reaction Force (CRF). Both bodies, i.e. Tori and Uke, experience the same magnitude of CRF but in opposite directions. The magnitude and direction of the CRF can be influenced by both Tori and Uke. The CRF also helps to keep both Tori and Uke balanced as it supports them as they apply force to each other i.e. the CRF is in the opposite direction to the propulsion force/momentum.
The direction of the CRF is the same when the body is pushing or resisting being pushed. Similarly, the direction of the CRF is in the same direction when the body is pulling or resisting being pulled, but this is in the opposite direction to that of pushing or resisting being pushed. As the direction of the CRF is the same for attack and defence the body balances the CRF in the same way as shown in the diagrams below.
When attacking, the propulsion leg moves the COM, by applying a torque to the ankles/feet, in the opposite direction to the expected CRF to position it so that both the propulsion force, i.e. ground reaction force, that is created by extending the propulsion leg against the ground and the torque exerted by gravity on the COM about the propulsion foot are increased to resist the effect of the CRF. At the same time, the momentum of the COM builds up to allow larger CRF forces to be created. The upper body then applies force to the target which generates the CRF at the contact point.
When resisting an attack, the upper body relaxes and does not oppose the attacking force, i.e. CRF remains at zero, until the lower body, i.e. legs/feet, moves the COM in the opposite direction to the expected CRF. This is in order to position the COM so that both the propulsion force on the COM and the torque exerted by gravity about the propulsion foot on the COM are increased to resist the effect of the CRF. At the same time, the momentum of the COM builds up to allow larger CRF forces to be resisted.
When recovering from a loss of balance, Uke uses the recovery foot to slow his momentum and keep his COM within his feet base. Uke does this by reversing the propulsion process using his recovery leg i.e. placing the recovery leg in the direction of motion and extending it against the ground. This has the effect of creating a ground reaction force which acts on Uke’s COM and decelerating it in the horizontal and vertical(downward) directions. However, the COM can still however rotate vertically about the recovery foot. This vertical rotary motion is slowed down by the muscles of Uke’s recovery leg applying torques about the foot and ankle joints in the opposite direction to the rotary motion. The effect of gravity on the COM will also create a torque about the recovery foot in the opposite direction to the motion. These torques help to prevent Uke’s COM from going beyond the recovery foot. However, if Uke’s recovery foot is not brought forward quickly so as to give sufficient time for these torques to slow down the COM, his COM will pass beyond the feet base and he will fall outside his feet base. (Wu et al, Robinovitch et al).
When Uke attacks, force is applied with his propulsion foot to move his COM towards the target and he is expecting to keep his balance with the help of the CRF or the Ground Reaction Force generated by his recovery leg. To unbalance Uke, this arrangement needs to be interfered with. The following courses of action are possible:-
Resist Uke’s momentum to create a CRF that slows his momentum to zero and then overcome Uke’s force so that he tips backwards about his propulsion foot.
Do not resist Uke’s momentum/force but limit him recovering with his recovery foot thereby reducing his stability in that direction. Uke can now be unbalanced in the direction of his original motion using only a small force.
The first method is dependent on strength, stability and technique and is generally employed in wrestling. The second method depends less on strength but more on technique and is employed in Jujutsu (Craig P27) and Judo (Watanabe and Avakian P36). In both methods Uke is unbalanced by Tori’s force.
A third method is proposed here that is a combination of the previous two methods where a part of Uke’s momentum/force is resisted and the remaining part is not resisted. The resisted part of Uke’s momentum/force assists Uke to keep his balance and therefore induces him to keep on applying force (in the original direction) as he becomes aware of becoming unbalanced in the direction of the unresisted part. In this way Uke is unbalanced by his own force. From studying the written and video material available, it is proposed that this method is used to unbalance Uke in the arts of Aikijujutsu and Aikido, that is referred to as Aiki. On this basis, a theoretical description of Aiki is given below.
In all three methods Uke needs to be prevented from recovering his balance, so that Tori can control him.
Theoretical Description of Aiki
Uke’s momentum/force UM/F is directional and therefore can be divided into two directional components which, when added together, are equivalent to the original momentum/force. For one of these components to be unopposed and the other fully resisted/balanced, the two components must be perpendicular to each other. At the Point of Application of this force/momentum the component that is resisted (URM/F) is directed radially towards a centre point and the unresisted component (UTM/F), at 90 degrees, is along a tangent of a circle about the centre point. In order not to resist UTM/F the Point of Application of the force is rotated in the same direction as UTM/F. When this is applied to the contact reaction force CRF or the recovery leg/foot force that Uke depends on to remain/recover balance, Uke becomes unbalanced.
It should be noted that in the situation where Uke is only holding, then Uke needs to be induced to pull or push so that he can be unbalanced by this method.
Once unbalanced, Uke will attempt to minimise forces applied to his body to avoid being thrown and recover by stepping. He will therefore willingly rotate joints when they are subjected to being twisted. Once a joint approaches its maximum rotation, Uke will rotate other joints to limit being thrown. This process can be used to induce Uke to bend at the waist which prevents straightening to step. The application of an atemi is also used to momentarily limit stepping, as is, turning Uke in a circle which induces him to bend to withdraw his hips.
Aiki Applied to Uke’s Recovery Foot Forces
In this case Uke is induced by Tori to apply Aiki in the vertical plane to his recovery leg when Uke’s COM (Point of Application of Uke’s momentum) has a momentum UM. Uke applies Aiki by being induced by Tori to reverse the torque in the joints of his recovery foot so that UTM is not resisted and Uke’s COM rotates about the recovery foot in the direction of UTM causing Uke to become unbalanced in that direction. The radial component of Uke’s momentum URM is towards the recovery foot and is balanced by the radial ground reaction force.
Aiki applied in this way to the recovery foot can be used to account for the unbalancing phase of a group of techniques demonstrated in the literature. The details of the unbalancing phase for a number of these techniques are given below.
Shioda, P 55. Uke attacks Tori to the side of the head using his right hand (Yokomenuchi). Tori steps forward to Uke’s left and uses his left hand to blend with Uke’s right arm and therefore does not stop Uke’s momentum so that he falls onto his recovery foot. Downward pressure on Uke’s attacking arm induces him to push upwards (Davey P85) by raising his heel and by doing so rotate his COM in the vertical plane about his recovery foot in the direction of UTM and become unbalanced to the front.
Tohei, P110/111. As Uke comes to strike the side of Uke’s head with his right hand, Tori steps back as he raises his arms to blend with Uke’s momentum. This induces Uke to use his ankle/feet joints to rotate his body in the vertical plane about his recovery foot to follow the target and become unbalanced to the front.
Yamada, P170/ Davey 137. As Uke attacks with a overhead sword/bokken strike, Tori steps forward and to the side. As Uke steps onto his recovery foot Tori applies an upward atemi to the solar plexus that induces Uke to lift his body, by raising his heal, to minimise impact and therefore rotates his body in the vertical plane about his recovery foot and become unbalanced to the front.
Ueshiba, P54. Tori offers his wrist to Uke. As Uke comes to grab Tori’s wrist, the wrist is withdrawn as Tori steps to the side. This induces Uke to rotate his body in the vertical plane about his recovery foot to follow the target and become unbalanced.
Aiki Applied to the Contact Reaction Force Experienced by Tori
Tori applies Aiki to the contact reaction force CRF he experiences by rotating the contact point (Point of Application of CRF) in a circular motion about a centre point in the direction of the tangential component of the CRF, i.e. UTF. The radial component, i.e. URF, of the CRF experienced by Tori that can either be towards or away from the centre point is opposed by the radial reaction force produced by Tori in the opposite direction. Uke is then unbalanced in the same direction that the contact point is moved in.
To move the contact point in a circular path around the centre point the radial distance needs to be kept constant during the rotation. This requires Tori’s body connecting the target to the centre to remain rigid. To achieve this, the connecting body parts are extended so as to become unbendable, as demonstrated in the unbendable arm by Tohei. Furthermore, the centre point must be kept stable by using the body joints and muscles to transmit the ground reaction forces and the gravitational force on Tori’s body to create the radial reaction force to balance URF.
Natural centres of rotation include the feet and body joints where the feet/joint rotation makes the contact point move in a circular path around the centre point. It is also possible to create virtual centres of rotation by moving the target in a circular motion about an imaginary centre point. In the latter case, the curvature of the circular path of the target determines where the centre of rotation is located. The movement of the target along a circular path in the direction of the tangential component of CRF will become obvious in practice as no resistance to the motion of the target should be experienced, whilst in the perpendicular direction the radial force is to be balanced. The circular motion of the contact point can be in the vertical plane, horizontal plane or any angle of plane in between.
The effect on Uke of Tori applying circular motion to the contact point can be experienced by Uke applying force to the free end of a hinged door. The rotating door is then acting as Tori.
Aiki applied in this way to the contact reaction force experienced by Tori can be used to account for the unbalancing phase of a group of techniques demonstrated in the literature. The details of the unbalancing phase for a number of these techniques are given below.
When Uke is Striking(Pushing) from the Front
Shioda, P 126/84. Tori blocks Uke’s overhead strike using his forearm, i.e. contact point. Uke is unbalanced by Tori rotating the contact point in a horizontal circular path, in the same direction as UTM/F, about a centre point vertically above his rear foot whilst balancing the pushing radial component (URM/F) with a pushing force.
Tohei, P120. Tori blocks Uke’s overhead strike and unbalances Uke by rotating the contact point in an upwards circular path, in the same direction as UTM/F, about the centre point of Tori’s shoulders. Uke’s radial pushing force is balanced by Tori’s pushing force. Saito demonstrated this technique in the First Friendship Demonstration video.
Shioda, P128. Uke applies a front punch to Tori’s solar plexus. Tori steps forward and to the side and secures Uke’s wrist, i.e. contact point, as he blends with the punch. Uke is unbalanced with a horizontal circular motion of the contact point, in the same direction as UTM/F, with the centre of rotation being above Tori’s left foot. Uke’s radial pushing force is balanced by Tori applying a pulling force.
Shioda, P21. Uke applies a strong front push with both hands to Tori’s shoulders. Uke is unbalanced with an upward circular motion of Tori’s shoulders, in the same direction as UTM/F, with the centre of rotation at a point to the rear of Uke’s shoulders the position of which depends on the curvature of the upward circular path of the shoulders. Uke’s radial pushing force is balanced by Tori’s pushing force.
When Uke is Pulling to the Front
Shioda P60. Uke is grasping Tori’s wrist, i.e. contact point, and pulling. Uke is unbalanced with a horizontal circular motion of Tori’s wrist, in the same direction as UTM/F, with the centre of the horizontal rotation positioned to the right side of Tori’s wrist, the exact position of which depends on the curvature of the circular path of Tori’s wrist. Uke’s radial pulling force is balanced by Tori’s pulling force.
Shioda P98. Uke is grasping Tori’s wrist, i.e. contact point, and pulling. Uke is unbalanced with a horizontal circular motion of Tori’s wrist, in the same direction as UTM/F with the centre of rotation located aboveTori’s front foot. Uke’s radial pulling force is balanced by Tori’s pulling force.
When Uke is Holding the Target
In this situation Uke needs to be induced to either pull or push so that he applies force to the target in order that Aiki can be applied.
Tohei P89. Uke grasps Tori wrist, i.e. contact point. Tori induces Uke to pull by moving behind Uke and then extending his arm and pushing on the back of Uke’s neck. Uke is then unbalanced to the side with a horizontal circular motion of the contact point, in the same direction as UTM/F, with the centre of rotation above Tori’s rear foot. Uke’s radial pulling force is balanced by Tori maintaining a pushing force.
Tohei P86. Uke grasps the outside of Tori’s wrist/forearm, i.e. contact point. Tori bends his wrist and advances towards Uke so as to rotate the contact point. This causes the back of the wrist/forearm to move towards the base of Uke’s thumb/index finger that induces Uke to push against a rotating target, in the same direction as UTM/F, and become unbalanced. Uke’s radial pushing force is balanced by Tori’s pushing force.
Ueshiba P75. Uke grasps Tori’s lapel, i.e. contact point. Tori induces Uke to pull backwards by applying an atemi to the face whilst stepping back and grasping Tori’s wrist. Tori bends at the waist to unbalance Uke by moving the contact point in a downwards circular motion about the waist, in the same direction as UTM/F. Uke’s radial pulling force is balanced by Tori’s pulling force.
Davey P89. Uke grasps the back of Tori’s wrist, i.e. contact point, as it advances towards him and pushes to stop its forward movement. Tori extends the arm and allows the arm to travel downward in a circular path, in the same direction as UTM/F, about his shoulder to unbalance Uke. Uke’s radial pushing force is balanced by Tori maintaining a pushing force.
Ueshiba P40. Both Uke and Tori are kneeling and Uke is grasping both of Tori’s wrists, i.e. contact points. Tori raises his wrists in an upward circular path about his shoulders. This action applies a force to the base of Uke’s thumb/index finger which induces him to pull. Uke is then unbalanced by the upward circular motion of the contact points, in the same direction as UTM/F. Uke’s radial pulling force is balanced by Tori’s pulling force.
Kondo P98. Uke grabs Tori’s wrists, i.e. contact points. Tori’s expands his wrists inducing Uke to concentrate on restraining Tori’s wrists. As Tori rotates his wrists they push against the base of Uke’s thumb/index fingers inducing Uke to push against a rotating target, in the same direction as UTM/F, and become unbalanced in a downward/forward direction. Uke’s radial pushing force is balanced by Tori’s pushing force.
Aiki applied to the Contact Reaction Force Experienced by Uke
In this case Tori induces Uke to apply Aiki to the contact reaction force Uke experiences as he applies force to Tori at the contact point. To see how this is possible, the internal body forces need to be considered. The internal body forces are used to maintain the body in a stable configuration to allow it to balance the effect of the contact reaction force CRF on the body, during pulling or pushing, with the effect of the ground reaction force and gravity.
When Uke applies force to the target and CRF is generated, each limb of his body that connects the contact point to the propulsion foot will generally experience an additional force at opposite ends of the limb, i.e at the ends connecting to the joints. When the limb is balanced, the end of the limb nearest the contact point will have an additional force in the direction of CRF and the end of the limb nearest the propulsion foot an additional force in the opposite direction equal in magnitude to CRF. These forces on the limb, called limb X, are illustrated in the figure below.
The component of CRF along the axis of the limb, i.e. RCRF, at the contact point end of the limb is balanced due to RCRF in the opposite direction at the other end of the limb. The latter force results from the support given by the limb next to it which, in turn, is supported by the other limbs leading down to the propulsion foot. The perpendicular component of CRF, i.e. TCRF, will attempt to rotate the limb. The body maintains stability by preventing the limb being rotated by using the muscles of the body to apply a torque to the limb in the opposite direction. Prior to applying force to the target, the body positions itself and applies the torque TY to the limbs of the body to resist the effects of TCRF when contact with Tori is made. It does this by starting from the propulsion foot and moving upwards so that the limbs below limits the rotation of the ones above.
Aiki can be applied to the contact reaction force CRF experienced by Uke at the joint (Point of Application of CRF) of limb X that is nearest to the contact point. This is done, by Tori inducing Uke to reverse the torque TY applied to limb X so that the limb moves in the same direction as TCRF around a centre point corresponding to the joint at the propulsion end joint of limb X. The contact radial force RCRF along the axis of the limb is balanced.
Aiki applied in this way to the contact reaction force experienced by Uke can be used to account for the unbalancing phase of a group of techniques demonstrated in the literature. The details of the unbalancing phase for a number of these techniques are given below.
When Uke is Striking (Pushing)
Kondo, P 48. Uke attacks Tori with an overhead strike (Shomenuchi). When Uke’s attack is blocked by Tori, Uke experiences a contact reaction force CRF. The upward pressure applied to the pressure point just above Uke’s elbow induces Uke to reverse the rotation of his rear lower leg, i.e. backwards, about the ankle joint to reduce the pressure on the pressure point. This action rotates the rear leg in the direction of the tangential component (TCRF) of CRF at the knee as the radial component (RCRF) is balanced. This unbalances Uke to the rear as he pushes.
Kondo P54. Uke applies a strike to the side of the head (Yokomenuchi). As Uke blocks the strike, he applies an atemi to Uke’s face which induces him to reverse the rotation of his lower rear leg about the ankle joint to minimise impact, as shown for Shomenuchi above, causing Uke to become unbalanced to the rear.
When Uke is Pulling
Kondo P66. Uke grabs Tori’s lapels and, as Uke pulls back, an atemi is applied to Uke’s solar plexus that induces Uke to reverse the rotation of his upper body by bending at the waist and by doing so becoming unbalanced to the front. This causes Uke’s shoulders to move in the same direction as the tangential component (TCRF) of CRF at the shoulders.
Kondo P60. Uke comes to grab Tori’s lapel. Tori moves backwards to extend Uke’s arm and applies an upward atemi which induces Uke to raise his front heel which rotates his body about his front foot joint, as he pulls back. This action unbalances Uke to the front by causing Uke’s heal to move in the same direction as the tangential component of the CRF at the heal. The upward atemi to Uke’s elbow prevents Uke from stepping forward to recover his balance.
The proposed explanation of Aiki, in its three forms, has been found to account for the unbalancing phase associated with many Aikido and Aikijujutsu techniques described in the literature and has highlighted differences between the Sensei. This fundamental understanding provides a useful starting point for analysing the early stages of a technique by allowing Aiki to be identified. This knowledge may also aid identification of actions prior to Aiki which are required to perform Aiki, as well as, post Aiki actions to prevent recovery of balance. It is hoped that this interpretation of Aiki will be of benefit to both beginners and more experienced practitioners and engender a deeper interest in the art of Aiki.
I apologise for any mistakes in this work that are subsequently found. Mistakes are possible given the difficulty in interpreting the interaction between Tori and Uke which is complex. However, I hope that this work is of some value to the practitioners of Aikido and Aikijujutsu and support the future development of these arts.
I would like to thank all the sensei that have documented their techniques and made them available in the public domain and in particular those that have been cited in this paper. I am also grateful to Aiki News for publishing many of the videos and books used in this research and the vast source of information available on their website and through their publications. I would also like to thank Sensei Isaac Coll and fellow students at Whitley Bay YMCA Aikido Club for their guidance and support during my early years of practicing Aikido. I would like to thank my wife Wendy, daughter Georgina and son Lawrence and grandchildren for their support and assistance. Finally, I would like to thank my friend Peter White for his invaluable computing assistance in bringing this paper to publication.
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