Research into the Development of Safe Kendo Training Equipment
text by Nakiri Fuminori (Tokyo University of Agriculture and Technology)

I Foreword
When discussing so-called modern kendo, we recognize the origins as being in the mid-Edo period when the shinai (bamboo practice sword) and bogu (protective equipment) were first introduced. Historically speaking however, the sword as a common combat weapon has been in use for a lot longer. Swords have been valued as important implements for war since recorded history. With the rise of bushi (samurai) as bands of professional warriors, and advancements in their methods of waging warfare, the sword took on new forms and began to evolve. The traditional tsurugi (double-edged blade) became the tachi (single edged blade with deep curvature) to facilitate one-handed fighting from horseback, and this evolved further into the katana (traditional samurai long sword), a weapon useful for combat at close-quarters and designed to be worn at all times.

During the peaceful Edo period, bushi continued to train in swordsmanship even though there were no more wars to fight. However, the standard method of training was to use bokuto (wooden swords) to practice kata (choreographed techniques.) Eventually a training system utilising the shinai became popular, and practitioners were able to uchikomi (strike each other) without fear of injury. (This method of training was referred to as shinai kenjutsu or shinai uchikomi-geiko or gekiken.) This was the precursor to modern kendo.

As suggested by the teachings setsunin-to (death dealing blade) and katsujin-to (life giving sword) from the Yagyu Shinkage-ryu tradition of swordsmanship, modern kendo has inherited the ideal of being primarily a form of human development or a vehicle for education. This ideal has been transmitted and developed through the centuries to the present day. The transformation from sword to shinai signifies a shift from combat weapon to a tool for education.
In this sense, a central concept for enjoyment of kendo as a form of athletic culture is “safety”. Using a bamboo sword to strike at designated targets on an opponent means that there is an inherent danger of inflicting injury. An extremely important factor for the development of kendo is how to make it as enjoyable and safe for practitioners as possible.

II Research Introduction
1. Shinai regulations and safety
As shinai are made from a natural material, i.e. bamboo, the fibres are apt to splinter in the course of use which can result in serious accidents. This has led to great expectations for developing alternative materials for making shinai. One such innovation was the Carbon Shinai made from synthetic materials. Wooden chips are glued together into slats, enveloped with carbon graphite, and finally covered with a plastic coating. After testing and comparing with standard bamboo shinai it was found that they were very springy and bent easily, making the largest shock value relatively small and the impulse power large. Therefore as individual differences and disparity in function are comparatively small, Carbon Shinai were officially authorized for use. Another cause of injury with the shinai is when the tip penetrates the bars on the men (face mask) and one or two slats of bamboo pierce the sakigawa (leather cap) and injure the eyes or surrounding area. In order to prevent such accidents from occurring, not only was the weight of the shinai regulated but the required total circumference of the tip was increased, and the length of the leather cap was also increased to 50mm. Furthermore, the position of the nakayui (leather tie holding the slats together in the mid-section of the blade) was fixed at 1/4 of the way down from the tip. These were some of the regulations introduced to improve the safety of shinai.

2. The safety of kendo-gu (kendo equipment)

In accidents caused by shinai entering the men, blame must also be allocated to the men-gane (metal grill on the face mask.) To remedy this, the circumference of the bars situated at the mono-mi (sixth and seventh bar down from the top of the mask) were increased by 0.5mm in order to strengthen them. Also, the space between the bars of the mono-mi was increased to 15 mm, and the height was unified at 75 mm (when the men-gane is placed on its side the distance from the outer circumference ring to the vertical bar running through the middle.)

Yuko-datotsu (a valid strike or point) is defined as “the accurate striking or thrusting with the shinai’s datotsu-bu (strike edge) to datotsu-bui (strike targets) on the hasuji (correct line), with full spirit, correct posture, and zanshin (mental and physical alertness against the opponents attack; positive follow through of attack and strike.)” However, the actual strength with which an attack should be made is extremely ambiguous. What then is the actual strength utilised when making a strike? Ascertaining such information is a particularly important fundamental investigation in order to assess kendo equipment safety. To conduct such an investigation we developed an apparatus to measure the strength applied when strikes are made to men, kote (forearm), or do (body), and when tsuki (thrusts to the throat) are made. It became apparent that the amount of strength applied differed depending on striking technique, the target, and the individual characteristics of the test subjects. Also, 3分力成分も異なることが明かとなった??? Based on this data, it was possible to set the required striking power in accordance with the disparity in shock absorbing qualities of the different pieces of equipment and the materials they were made from. Using an apparatus for generating striking power and measuring equipment, we were able to test the shock absorbent capability of kendo protective equipment―particularly men and kote padding, tsuki-dare and yojin-dare (throat protectors), and do (body armor). We found that when the padding was roughly stitched with 2-bu 5-rin stiching, it was more shock absorbent than the higher quality, finer 1-bu stitching. We also found that as a core material, cotton with its airy qualities made it more shock absorbent than felt. Furthermore, we found that the shock absorbent qualities of synthetic materials could be used when these qualities had been enhanced. We also discovered that kote padding was less absorbent than men padding. According to the most recent research into striking power, the shock from making a basic kote strike with a furikaburi (big overhead preparatory movement) is larger than a strike to the men. The discovery of this contradiction means that we need to reassess equipment standards. Furthermore, the striking power initiated by elementary school students is surprisingly large and is particularly noticeable in basic technique training. Despite this, protective equipment utilised by elementary students is characteristically flimsy and shock absorbing qualities are low. Taking this into consideration, there is a need to utilise materials that are more absorbent, and also be vigilant when making strikes against children.

With the introduction of the Product Liability Act in 1995, the Budo Yohin Kogyokai (Budo Goods Manufacture Association) and the Zenkoku Budogu Rengokai (National Budo Equipment Union) formulated specific regulations for the manufacture of kendo equipment in accordance with the 1998 Product Safety Council. Until this time, specific regulations did not exist, and so it was a milestone for the kendo world, which had continued to manufacture equipment based only on tradition and individual experience. The content of these regulations were designed to ensure the maintenance of minimum requirements of shock absorbent qualities for safety reasons. The dimensions of the equipment, method of construction, and materials were specified in detail, and this served to enhance safety to an unprecedented level. Taking into consideration the international spread of kendo and the fact that a significant proportion of equipment is now being produced overseas (China), it is vitally important that we make international regulations pertaining to kendo equipment, and this needs to be done with a broad perspective.

As these standards are based on the physical qualities of kendo equipment already on the market, can we be sure that equipment already in circulation is truly safe and of a high safety standard? Furthermore, don’t we need to try to make kendo equipment even safer? These are basic problems that come to mind. If we look at kendo as being a lifelong pursuit, more attention needs to be paid to the health and safety of elderly practitioners, and also to the changing physiques of younger generations and the larger physiques of foreign practitioners. These are central issues which require more thought and consideration. We also conducted a simulation to ascertain the influence of the shock that passes through the protective equipment onto the brain and neck area when struck. We attached a men to a crash test dummy and used sensors to obtain readings of speed change and tri-axial loadings on the neck and instants of tri-axial rotations. Through this we were able to calculate the effects of shock inflicted on the head and neck. Using the results of this experiment we utilised head tolerance curvilinear data from the Japan Automobile Research Institute as a basis and ascertained that the probability of any damage to the head (traumatic brain injury, concussion etc.) through one strike was extremely low. However, the influence of repetitive strikes to the head is an area in need of further investigation.

Direct impact from power generated from tsuki is impeded by the tsuki-dare and the yojin-dare. However, there was an example of a tragic death following damage to the jugular vein and arteries, which caused a blood clot resulting in cerebral infarction. Therefore, we can draw the conclusion that research is urgently needed into ways to make equipment safer.