Tuesday, May 8, 2012

Straight Arm Lock/Arm Bar/Ude Kujiki - Take Two

I originally posted this blog using a particular image of what appeared to be the defender stepping toward the attacker when executing the technique. I used this image as it highlighted a particular issue I wanted to explore, however, it was pointed out to me that the technique in question, while looking similar to the straight arm lock under review, was actually different and is the applied forces are intended to produce a different affect. I take that comment on board and apologise unreservedly for taking licence with that image. This blog recasts the previous with a more appropriate image. For those who have already read this blog (and there have been quite a few of you) the amendments are contained in the end part of this blog. This has also given me the opportunity of including a little more information which I neglected to include in the original of this blog.

I've recently been contacted by a group of fellow martial artists who are interested in the biomechanics of the martial arts. The interaction reminded me of the work I commenced on understanding joint-locking techniques (kansetsu waza).

The photograph to the right is of a straight arm lock, also commonly known as an 'arm bar', and in Japanese as ude kujiki. The photograph is not the greatest, but it was taken at the late Greg Palmer's dojo with two of his former junior students. Greg was a senior instructor of Jan de Jong, was one of my instructors, had a depth of understanding and love of jujutsu possibly second to none at the Jan de Jong Self Defence School, and became a friend and training partner of mine. Out of respect and in memory of Sensei Palmer, I'll use this photograph for illustration purposes.

The straight arm lock is a technique taught by many, if not most, martial arts. It is one of the few kansetsu waza which is permitted in judo competition, and is often seen in mixed martial arts competitions. It can be applied using the arm, as in the photograph above, or the hip while lying on your back, as in the photo to the right. It can also be applied with the leg, hip while standing, stomach, hand, forearm, shoulder, neck, head, and with weapons.

Jan de Jong included theory gradings in his dan (black belt) grades. These are oral gradings which examine the candidates knowledge of techniques and tactics, the proficiency being taken as given. If a black belt represents a teaching qualification, as it most definitely does in Jan de Jong jujutsu, the candidate's theoretical knowledge should most definitely be examined.

How do you study for this theory grading? Unfortunately biomechanics in biomechanical or martial arts texts will not be of much help. Vieten (2008) provides an overview of the English-language martial arts literature related to biomechanics. He found the percentage of biomechanics papers among the literature in martial arts is very low compared to some popular sports and suggests ‘the biomechanics of the martial arts is still in its infancy’ (562). Too true. My work is about growing that infant. This blog is about growing that infant, and possibly encouraging others more qualified than myself to take up the challenge.

Welcome to your theory grading, or part thereof. A typical question De Jong would ask, and which Palmer often referred to when explaining the theory examination, was: What are the forces involved in ude gatame ude kujiki (arm set arm breaking; the first techique illustrated above)? This, as it turns out, was a very insightful question. The problem was that De Jong and the candidates only had a layperson's understanding of 'forces'. If they'd have had a mechanical/biomechanical understanding of forces, the answers would have not be so convoluted.

Kreighbaum and Barthels (1996; K&B) explain that 'because forces account for the motion and changes of motion of all things in the environment, including the body and the body segments, it is important for the movement specialist to understand what forces are and how we can picture them as they are applied to or by the body' (80). Firstly, 'a force is something that causes or tends to cause a change in the motion or shape of an object or body' (80). It's not just a change in motion which forces cause; they also cause a change in shape which is referred to as 'deformation' in mechanics. If the deformation of the body's tissues is significant enough, it will lead to injury. Secondly, given the preceding explanation of forces, it is important for martial arts instructors and students to understand what forces are and how they can picture them as they are applied to or by the body. The beauty of it all is that it is so easy - 'easy peesy Japanesey.'

'A force can be thought of as a push or a pull; ... a blow or impact, or gravity' (K&B 1996: 80). Forces have four unique properties: magnitude, direction, point of application, and line of action (K&B 1996). In initially answering our theory question, all we need to do is identify all of the points of application and describe their direction and whether they are a push or a pull. That is it - easy peesy Japanesey. Forces are what makes the technique work. They are the essence of the technique.

See: http://www.kojutsukan.blogspot.com.au/2011/06/using-forces-to-understand-and-explain.html

With the ude gatame ude kujiki, there are three points of application. The right hand is applying a pushing force to the back of uke's (receiver of the technique) flexed hand back towards uke; the left hand is grasping and applying a pulling force on uke's wrist away from uke; and the elbow is applying a downward force to uke's elbow. That is it - easy peesy Japanesey. Next question.

What is the purpose of ude gatame ude kujiki, or any kansetsu waza for that matter? Kansetsu waza is a seperate class of technique. This can be seen in numerous texts and in numerous systems. For instance, the Kodokan Judo classification of techniques initially classifies all their techniques as nage waza (throwing techniques), atemi waza (striking techniques), and katame waza (grappling techniques). Katame waza is subdivided as osae komi waza (immobilisation techniques), shime waza (strangulation or choking techniques), and kansetsu waza (joint locking techniques).

The kata gatame ude kujiki (shoulder set arm breaking) illustrated to the right can be turned into a shoulder throw. In jujutsu, throws often involve initially locking up the joint in order to throw an opponent. They are also used to take an opponent to the ground without causing both the opponent's feet to leave the ground. This is my biomechancially-based definition of a takedown technique. Kansetsu waza are often used as immobilisation techniques, as is often seen in aikido. They are also used as kuzushi* (unbalancing) techniques. They are used as pain compliance techniques, and, which is probably the first explanation that would most likely be given, they are used to disable an opponent by injuring their joint. If I was examining a candidate and they gave me the last answer, I'd immediately ask them how often is the ubiquitous wrist twist used to disable an opponent by injuring their wrist. The humble wrist twist is most often used to take an opponent to the ground (takedown technique not a throwing technique as is so often described in aikido and many jujutsu systems)in order to execute another technique, a 'finishing' technique.

Firstly, it can be seen that kansetsu waza is a class of technique which overlaps with many other classes of techniques. It has multiple personalities. Secondly, so what? So what? The technique may look the same, that is to say it has the same points of application of the forces, but the direction and magnitude of the forces will differ depending on the purpose of the technique.

What is the physiological effect of applying forces to the extended elbow when executing ude kujiki? Here there is no authoritative answer. I was astounded, when researching the science behind joint locking techniques, that I could find no detailed explanation of the effects of kansetsu waza when forces are applied and the joint is moved beyond its range of motion. If any reader knows of such information, and only authoritative information is of interest, I'd appreciate it being forwarded to me and I will duly share it with the world via this blog.

Why not refer to medical or forensic texts? I did. However, between 80% and 90% of all injuries that occur to the upper limb are the result of a fall on an outstretched hand (FOOSH injuries; see http://http://www.kojutsukan.blogspot.com.au/search/label/FOOSH). Consequently, the medical and forensic literature focuses on these types of injuries. The forces are applied in a different direction when landing on an outstretched hand compared to when forces are applied at right angles to the posterior aspect of the elbow when executing an ude kujiki.

The bones of the elbow joint are the humerus, radius, and ulna. The olecranon of the head of the ulna fits into the olecranon fossa of the humerus which limits the hyperextension of the forearm and provides stability to the joint. Dislocation refers to the complete disruption of of a joint so that the articular surfaces are no longer in contact. Dislocation of the elbow results in, among other things, extreme pain and inability to move the elbow. Elbow dislocations are classified with reference to the position of the ulna relative to the humerus following injury. Dislocation of the elbow can be posterior or anterior:

  • posterior – the forearm bones are displaced posterior to the distal part of the humerusand accounts for the majority of all elbow dislocation injuries.
  • anterior - the forearm bones are displaced anterior to the distal part of the humerus and are extremely rare. Consequently the data on these types of injury are likewise rare.
In layperson terms, with a FOOSH injury more than 90% of the dislocations of the elbow involve the ulna sliding up the back of the humerus because the forces are being transferred from the hand to the forearm and to the elbow. The forces are applied in a different direction when an ude kujiki technique is executed; they are applied to the posterior aspect of the elbow, which means the injury may be different. After all, Whiting and Zernicke (2008) include in their seven factors which combine to determine the nature of an injury, the tissues injured, and the severity of an injury, 'direction (where is the force directed?)'.

Anterior dislocations are often described as occurring when the elbow is flexed and it receives a blow. The olecranon can lever the humerus and slide in front of it, or, it can be fractured. This is often referred to as a 'fracture-dislocation'.

I apologise for not being able to identify the source of the following quote. It is included in my notes without reference, and I need to go back to my notebooks to identify the reference. However for the purposes of this blog I will proceed without the reference.

Given elbow dislocations are the one joint technique allowable in judo (wrist, shoulder, and knee techniques were forbidden due to the risks of injury associated with the techniques), a sport practiced around the world for a century, and there is no reference I can find in the literature on extreme elbow injuries as in the case of a fracture-dislocation in judo, I might hypothesise that the abovementioned dislocations without fractures are not uncommon when an external force is applied to the posterior aspect of the elbow.
What type of dislocation and injury occurs when executing ude kujiki? Given they are permitted and used in judo and mixed martial arts, you might have thought there would be information published on this issue. You might have thought wrong. If I am mistaken, I'd appreciate reader's directing me to the source that would correct my misunderstanding. This blog is, as stated above, a call to arms to encourage others to study these most basic of questions: What injuries are intended to be inflicted when a joint-locking technique is executed? In the case of ude kujiki, in my mind it is the comparatively rare anterior dislocation with a possible fracture of the olecranon

The technique to the right is described as a 'step in arm lock.' Comment on the technique? This is a question which De Jong would often pose using photographs from books, etc? Firstly, a tactical issue. Stepping toward the opponent while applying this technique exposes the defender to the risks posed by the attacker's free hand. Secondly, stepping forward changes the forces applied by the hand at the wrist. Now it is pushing rather than pulling. This has the effect of 'close packing' the elbow joint increasing rather than decreasing its stability (increasing rather than decreasing its resistance to forces). Thirdly, I would hypothesise that should the combined forces result in a dislocation of the elbow, it would result in a posterior dislocation whereas when forces are applied to stretch the elbow joint and then forces applied to the posterior aspect of the elbow, they might result in an anterior dislocation and/or a disclocation-fracture.


*Interestingly, Jigoro Kano explains that 'the basis of kuzushi is pushing and pulling' (1986: 42). Kano, the originator of the use of biomechanics to understand and study the tactics and techniques of the martial arts - to a degree and possibly unwittingly.


Kano, J. (1986). Kodokan Judo. Tokyo: Kondansha International

Kreighbaum, E. and K.M. Barthels. (1996). Biomechanics: A qualitative approach for studying human movement. 4th edn. Boston, Massachusetts: Allyn and Bacon.

Vieten, M.M. (2008). Application of biomechanics in martial art training. In Handbook of biomechanics and human movement science, edited by Y. Hong and R. Bartlett. Abingdon, Oxon: Routledge.

Whiting, W.C. and R.F. Zernicke. (2008). Biomechanics of musculoskeletal injury.2nd edn. Champaign, Illinois: Human Kinetics.


  1. John, check out the recent strikeforce title fight between Rhonda Rousey and Meisha Tate - Rousey, a Judo Olympian, destroys the arm with a straight arm lock, she did the same on her previous fight as well. Its interesting that both the opponents were not 'devastated' by this injury, perhaps with this type of dislocation, a lot of the damage is tissue damage, and you will feel it worst in half an hours time (granted they are tough as well).
    All the best,

  2. Paul, that is truly cringing. What I wouldn't give to get a copy of the x-ray to see the dislocation. I'm not sure whether to admire Tate for her efforts or criticise her for her stupidity. 'Tap, you stupid woman, tap.' It is interesting, as you say, it wasn't devastating in an emotional sense, but I'm suggesting that arm was effectively useless from there on and would pay no further part in any fight that continued thereafter.


Your comments make my work all the more relevant as I use them to direct my research and theorising. Thank you.