It is no secret that Tomiki Aikido practitioners in the United States tend to experience significant injuries. It is rare to encounter a practitioner who has not had a serious injury, usually related to a competitive skill, at some point. Much of this is due to a lack of solid understanding of biomechanics within the art, and this is symptomatic of the nature of the art in relationship to the typical structure and habits of American practitioners.

In Sports Biomechanics, Melanie Bussey defines a sports injury as “the disruption or failure of biological tissue in response to mechanical loading during sporting endeavours.”[1] These types of injuries can be categorized in several ways, but in this case, we will follow the categories in this table.

Table. Categories of Sports Injury
ContactRubbing, Chafing, Grinding
OveruseDynamic Fatigue of Tissues 
Structural Vulnerability Weak points or load failure under stress
InflexibilityBound axes of rotational or linear movement
ImpactFracturing or bruising from force trauma
Rapid GrowthAdverse healing or scarring, swelling

 Some of these categories are simply unavoidable and unpredictable. Impact injuries, which include concussions and inadvertent strikes can cause significant, instantaneous damage. Others, such as contact injuries, occur over time. They can be cumulative. They can also be related. Inflexibility in the lower back can produce structural vulnerability. Contact injuries, especially in the joints, can result in spurring, slipping and the consequential body compensations. Injuries cannot be avoided altogether. Often they are incidental. Risk factors can, however, be identified and the practitioner can take steps to both mitigate the potential of injury and to identify the actual processes which might lead to injury. In this paper, the issues to be addressed will be biomechanical. This means they will address the forces and force-related (mechanical) factors which contribute to potential injury. There are a large number of principles that could be addressed in this area, but this paper will focus on two of them: structure to manage energy, awareness of resilience and fatigue. These are principles to be explored and developed primarily in the taking of ukemi

Injury Comes from Receiving More Force Load than Your Body Structure Can Handle,
Change Your Structure to Manage the Energy

The working definition at the beginning of this paper describes “mechanical loading” as the cause of injury. This occurs when a force introduces more energy into a mechanical system than the system can properly utilize or dissipate. Much of the ukemi training in aikido is built around the idea of redirecting and dissipating force from your partner’s attack. Unfortunately, the emphasis is often on the ukemi of falling, with little focus on the internal body mechanics of redirecting the energy within the body.

Let’s begin with a question? When can the introduction of energy to the body do damage? When it is focused on a component of a system which can be overloaded. Consider the potential energy of a properly performed kote gaeshithrow. Tori projects a great deal of energy stored in the legs and core through his hands and into uke’s wrist and forearm. We are generally taught that the only defense is to perform tobi ukemi to release the energy and prevent injury. The technique is only effective as long as all the force is directed to the wrist. If, however, uke is able to redirect the force into a larger body component, then such large ukemi is not required.

Load is the sum of external forces applied to a material or tissue. Somewhat counterintuitively, load is almost never equal to the total energy being exerted. This is because a lot of the energy tori uses will be directed somewhere other than the load point. So, load is equal to the sum of the forces generated minus the forces lost. The less the loss, the greater the load uke has to deal with. Conversely, the more uke can redirect and misalign the application of force, the less the load he has to manage. 

This concept is difficult to express but it can be experienced through a dojo experiment. Allow someone to use kote gaeshi on one of your arms. At the point of kuzushi, place your free hand over your partner’s hands and press lightly toward his center, along the bones of his forearm. The change of direction closes a loop of the force load, sending it back to your partner, alleviating the kote gaeshi and allowing you to maintain your balance. It will not completely reduce the stress of the technique, but will redirect a portion of it. This is, in effect, making tori a part of your kinematic chain (more anon), and putting part of the load into his body as a component of your system. At a high level, such chain realignment can be done within your own body structure.

Without getting into any more physics than necessary, good ukemi does not simply fall away from the load point. It also spreads the load out as much as possible. Change must be relative to the force load, which means it is not necessarily any one direction. It must be direction and alignment relative to the force load. If F=ma, then the mass of the partner is non-variable, but acceleration can be changed.[2] Force is energy applied to an object. Acceleration is change of speed over the vector of distance. Minimal change to a large object, such as a human being, can accelerate a great deal of its mass in directions other than optimal, reducing the force load significantly.

Imagine a bullet being fired at the surface of water. Fired at an angle of 90º to the water, the projectile would pierce the water without any significant change in direction. Fired at an angle of less than 30º, the bullet may ricochet off the water like a skipping rock. Why? Because the force of the bullet at that shallow angle is less than the force of the surface tension of the water. The molecules of the water push back against the bullet and reflect it. The angle of acceleration results in a reduction of the force load.

In the same way, you can change your structure as to change the angle of acceleration of tori’s technique. Two vital components should be explored here. First, the kinematic chains, the series of muscles, joints and connective tissue that are brought out of alignment through a technique (in our example, kote gaeshi).[3] The wrist and forearm are levers, deforming a complex kinematic chain that causes the entire body to move. You, uke, are in what is called an ineffective kinematic chain. The structure is insufficient to properly direct the force. To counter this, you must shift to and maintain a properly aligned kinematic chain, one which dissipates the energy of the technique while maintaining its own integrity. The force of the attack quite literally ricochets off structure. This is a gross oversimplification of the reality, but it hopefully demonstrates the point. This is considered an effective kinematic chain. Additionally, if you can create an effective kinematic chain in your own body while compromising your opponent’s kinematic chain, the net result is significantly increased.

The second vital concept to be embraced is rotational movement rather linear movement. Change of kinematic chain is often (but not always) the result of rotational alteration of structure to bring the chain into better alignment. Linear movement has a finite number of angles, chiefly the parallel and perpendicular. Rotational movement, however, can quite literally “wrap” the energy and dissipate it more easily. 

Of course the relationships are complex and the body is a composite of numerous mechanical operations. Experimentation and inquiry is the only way to learn how force load can be distributed. Experience is a better teacher than mathematical analysis, but the analysis reveals that with intentional practice one can develop the skills to do so. In developing these skills, you reduce the risk of injury by preventing too great a force load on any specific area.

The Relationship of Strain to Fatigue Injury Is a Steep Curve
Develop Awareness of Change in Resilience

Strain is a relative measure of deformation of tissue.[4] Resilience is a measure of the energy absorbed by a the tissue that is returned when the load is removed. In other words, resilience is how well your tissues recover from repeated strain and a measure of what is lost with each deformation. Fatigue is the opposite of resilience. It is the ability or energy that is lost when the load is removed. Put more plainly, resilience is how much strength you have when a load is removed. Fatigue is how much you lost.

Muscles and tendons have elasticity limits, meaning they can be put under stress a finite number of times. Think of snapping an old wire hanger. The first time you bend it, the metal resists your efforts. It has strong resilience. Repeat the bending. At first, you will see no change but after several repetitions, the metal fatigues and simply snaps in half. This is because fatigue is not a linear value. With repetition, the amount of fatigue per repetition increases. Failure is the cumulative result, but the final “snap” occurs suddenly. 

All human tissues (muscle, bone, etc.) are viscoelastic. It deforms slowly under load. This means that short, sudden impacts can do more damage than prolonged stress.[5] If a body part is put under load with proper balance and alignment, it can adjust to the load maintain load-bearing without damage for a significant period. Also, if the body part is taken to the point of the fatigue curve and then allowed to recover, the tissue will develop strength and greater resilience. If the same tissue is put under load suddenly and intensely without recovery, it can be damaged quickly.[6] As the tissue is deformed and then restored repeatedly, the loss of resilience and increase of fatigue causes a loss of alignment and integrity. Once fatigue begins increasing on the high end of the curve, the potential of injury from suddenly increased load becomes high. The more fatigued your tissues are, the more likely you are to injure them in a sudden impact or act. 

In aikido, we experience fatigue most often when performing tasks with the wrong muscle groups. Small muscle groups such as the rotator cuff muscles (supraspinatus, infraspinatus, Teres Minor, and Subscapularis) may be called upon to perform tasks that could be handled much more efficiently and more resiliently by the much larger muscle groups of the back and legs. The knees are torqued to produce a single direction pulling rotational force that could be generated more easily with a contra lateral movement powered by the glutes and abdominals.[7] The brachii (bicep and tricep) can be strained by doing lifting that could be done with the torso muscle groups. 

The biomechanical solution to fatigue is to develop and align the correct musculo-fascial kinematic chains and then use them to power movement correctly rather than using small, isolated muscle groups. Essentially, this “flattens” the curve of fatigue by transferring load-bearing into the coordinated movement of large possible muscle groups through proper kinematic chaining. It is analogous to shifting smoothly from first to fifth gear smoothly in a car. Identifying the best “gear” for movement at various stages is a key to avoiding fatigue as well as developing resilience through muscle training.

Consider the idea of “pulling” a gripping hand into your control. A remedial student might approach this by pulling the arm back, trying to bend it at the elbow. The primary muscles that are contracting are the deltoid (shoulder) and the brachio radialis (in the forearm). The elbow is tensed and tightened to even begin the motion. These two muscle groups can generate considerable force, but they result in tension in the arm and fatigue quickly if the motion is sustained or repeated. The arm also has to be drawn a considerable distance before the muscles can engage fully. A better drawing effect can be created by relaxing the shoulder muscle group and allowing the serratus anterior muscles to draw the scapula down. If the muscular movement can be connected to a rising movement from the front abdominal muscle group, the result is circular movement that draws the gripping hand into your control.[8]

To prevent strain injuries, it is vital that the practitioner develop body awareness. This cannot simply be spatial awareness, which is what is often taught. It must be movement awareness on the musculo-fascial level. As you move, what muscles contract? What muscles expand? What is the relationship between them? What large muscles are engaged? The body awareness is almost the inverse of weight-training, which looks to isolate muscle groups. In this awareness, the sensitivity must be to the body as a whole and how the connections can be aligned, strengthened and utilized more efficiently under load. 


Tomiki Aikido has many hallmarks of a contact sport. Injuries are inevitable, especially since it is practiced by amateurs, often without rudimentary practices in place to counteract the potential risks. Traditional stretching exercises, long held to be the key to longevity may actually contribute to the risk potential if not practiced with body awareness or focused on the ideal muscle dynamics of weight training or running sports. Ultimately, a unique protocol should be developed beyond the traditional stretching and warmups. One element of this preparation should be the use of foam and wood rollers to lengthen and free muscular tissue and loosen fasciae binding. There should also be a regiment of range of motion exercises, particularly for the joints. Elbow, shoulder, hip, knee and ankle mobility can be increased through range of motion drills, minimizing the risk not only to the joints but also the connective tissue. 

This paper is not exhaustive. It is exploratory. It is a beginning, with the hope of developing a deeper understanding of the biomechanical responses and risks inherent to Tomiki Aikido. There is a great deal more to be done in this area to safeguard the next generation of practitioners. 


Agitan, Sendar. “Biomechanics Measurement Methods to Analyze the Mechanisms of Sports Injuries,” in Sports Injuries: Prevention, Diagnosis, Treatments and Rehabilitation, 19-26. Berlin: Springer, 2012.

Bussey, Melanie. Sports Biomechanics: Reducing Injury Risk and Improving Sports Performance. London: Routledge, 2012.

Joyce, David. Sports Injury Prevention and Rehabilitation: Integrating Medicine and Science for Performance Solutions. London: Routledge, 2015.

Watkins, James. Fundamentals Biomechanics of Sport and Exercise. London: Routledge, 2014.

[1] Melanie Bussey, Sports Biomechanics: Reducing Injury Risk and Improving Sports Performance (London: Routledge, 2012), 2.

[2] Force = mass x acceleration is the classic Newtonian formulation for force.

[3] Kinematic chains are a difficult concept. For reference, consult David Joyce, Sports Injury Prevention and Rehabilitation: Integrating Medicine and Science for Performance Solutions (London: Routledge, 2015), 78-81.

[4] Bussey, Sports Biomechanics, 14.

[5] James Watkins, Fundamentals Biomechanics of Sport and Exercise (London: Routledge, 2014), 168-169.

[6] Bussey, Sports Biomechanics, 42.

[7] Contralateral movement is not something we have room to explore. In body dynamics, it is the idea of opposing muscle groups learning from each other, moving in opposition to accomplish force. It is the “go up to go down” of so much of aiki. It can also be referred to as pull-push or down-up cooperative movement between opposite sides of the body or even opposing muscle groups within a single limb or joint. It is a subtle type of movement that take considerable practice.

[8] This down/up motion is taught in the practices of some Daito Ryu Aikijujutsu schools but rarely talked about in aikido. I acquired it from training with Daito Ryu Aikijujutsu Ginjukai, Howard Popkin Sensei and Joe Brogna Sensei, but it has been referenced in other schools. 



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