Applying Aiki


To understand how to apply Aiki it is necessary to have some knowledge of the biomechanics involved in the movement and application of force by Uke and Tori.  The following paragraphs summarise this information which will help understand the analysis of how Aiki is applied in the YouTube videos given in the following pages.


Maintaining Balance



In general, when Uke attacks Tori he uses his rear leg to apply the force that is needed to increase his momentum to move his body towards the target/contact point. On contact with Tori, Uke will experience a contact force the direction of which will be determined by whether Uke is pushing or pulling with his arms. If Uke is simply holding Tori the contact force is zero. Uke resists the unbalancing effect of his momentum and the subsequent contact force by using the ground reaction force produced at the base of his feet and the gravitational force due to his weight.  The direction and magnitude of these two balancing forces are controlled by the position of Uke’s joints at the waist, knees, ankles and feet and the torque (rotary force) that the muscles exert about these joints.

As Uke makes contact with Tori, Tori will experience the same magnitude of contact force as Uke but in the opposite direction. The actions of both Uke and Tori determine the contact force and therefore their balance. For example, if Tori does not resist Uke's attempt to pull or push, the contact force for both of them becomes zero. Normally, a sudden change in the direction of the contact force by the actions of either Uke or Tori would lead to them both becoming unbalanced. This is prevented by them instantly relaxing their upper body muscles to reduce the contact force to zero allowing them the freedom of movement to reposition their joints before balancing the new direction of the contact force. 



Applying Aiki


This section summarises the three forms of Aiki and how these forms can been applied by Tori to unbalance Uke.  Video footage, available on the internet, has provided the source material for bio-mechanically analysing how Aiki has been applied. This has resulted in being able to identify a small number of fundamental methods by which Aiki can be implemented that is in keeping with the following definition of Aiki.

Aiki is a method of unbalancing Uke by reversing a muscular torque that Uke depends on to maintain his balance.

Form 1. As Uke advances towards Tori (zero contact force), Tori induces Uke to apply Aiki by reversing a muscular torque in Uke's front leg that he normally uses to slow down his momentum as he steps forward. Consequently, Uke becomes unbalanced to his front. For example, this can be achieved by Tori withdrawing the target just before contact is made, applying a light-touch downward force or applying an atemi as Uke steps forward. Since there is no substantial contact between Tori and Uke, Tori’s balance is unaffected.



Form 2. As Uke applies force to the contact point, Tori applies Aiki by reversing a muscular torque so as to rotate the contact point about a joint/centre point. Consequently, Uke's force is no longer balanced in this circular direction and he becomes unbalanced. Tori stays balanced by balancing the radial component of Uke's force as he rotates the contact point about the joint/centre point. This form of Aiki appears to be used mainly in Aikido.



Form 3. Tori induces Uke to apply Aiki by reversing a muscular torque that Uke normally needs to maintain his balance. This is achieved using the following methods:-

  • If the contact force is zero, Tori applies a force to the contact point which will elicit Uke’s natural response to relax his upper body, allowing him the freedom of movement to reorientate his lower body and apply force to increase his momentum, before applying force with his upper body to the contact point to counter Tori’s force/movement. Tori exploits Uke’s initial response of relaxing his upper body to induce Uke to apply Aiki by adjusting the orientation/position of the contact point or applying an atemi. The duration that Uke relaxes his upper body increases with the size of Tori’s initial force. Large initial body movements by Tori that could unbalance Uke to the side will require Uke to take a longer time(upper body relaxation period) to reorientate his lower body than if Tori applied a smaller force directly at Uke. The former case is more common in Aikido whilst the latter is more commonly demonstrated in Aikijujutsu which uses small body movements which are rapid enough to fit within the smaller relaxation period.                                                
  • If Uke is applying force to the contact point, Tori reduces the contact force to zero by going with Uke's force which induces Uke to relax his upper body which can be exploited by Tori to induce Uke to apply Aiki by adjusting the orientation/position of the contact point or applying an atemi. 

  • If Uke is applying force to the contact point, Tori resists Uke’s force and induces Uke to apply Aiki by applying, for example, an atemi, a force to a pressure point/locked joint or pinch to the skin. Consequently, Uke reverses a muscular torque that he normally uses to balance the contact force and therefore becomes unbalanced. Tori retains his balance by stepping. These techniques are commonly used in Aikijujutsu.