Ryvai wrote:Recently the board in our club has been discussing bying some land and building our own dojo (entire building). During the discussions I came to think of the tatami at the Kodokan. I've never been thrown on such a comfortable tatami ever since. Do you guys have any experience or advice as to building a perfect tatami subfloor? I.e spring effect, like they have in the main dojo of Kodokan.
I've read this article, and it seems to bring up some interesting idea's:
The foam solution seems to be a very good alternative, what do you guys think?
I conducted an extensive study of this, but I have not written out my research. I also wrote a long post about it here on the forum, but I deleted it after receiving some emotional outburst(s). When I do things, as a scientist, I am driven by accuracy. This often conflicts with jûdô where many other factors dominate, such as personal likes and dislikes for people, domination by high ranks rather than by scientific accuracy, etc. This is a difficult relationship and this difficult relationship between judo and science exists in Japan too. Much of what is accepted about judo originates at the Kôdôkan where ideological truth is established by those with the highest rank. A parallel circuit exists where scientific truth is pursued by those at academic institution independent of ideologies distributed at the Kôdôkan.
The situation is not any different for floors and tatami. The reality for the judo audience is one of financial, organizational and other limits. People often want a quick solution, limited investment in terms of effort, etc, and that is different from the science. Besides, I perceive that in judo many are not even willing to read the information even if available. When I did the research I looked up all existing studies and papers, and compared all systems in different as well as how the efficiency of the tests and how they were conducted. There is some really good research on this, including by a forum member here, although that is limited to tatami research. But, as usual, most people who are good in their part of science are not at the same time experts in other sciences or knowledge, specifically they usually do not read Japanese, thus the Japanese research is not included in what they do. The Japanese are immensely further evolved when it comes to tatami and judo dojo systems than the West, and when one has actually studied the situation in depth, the situation becomes acutely aware of the hilarious and often painful situation that exists.
I have seen posts on this forum where high federation officials announced the sales of tatami announcing them as "the best in the world". One must not realize how embarrassing such as statement really is. Western tatami do not compare to Japanese tatami, but unless one knows what to look for and knows what one is talking about, one obviously does not know. Western judo tatami simply contain a piece of polyurethane wrapped in a vinyl-like material that is glued together. But Japanese judo tatami are immensely more engineered. To start with, Japanese tatami are actually stitched, not just glued. Western tatami manufacturers do not have the machines to stitch tatami. So you sometimes see Western tatami after high humidity in the dôjô simply fall apart when the glue comes undone. No such thing with Japanese tatami. Japanese tatami contain different layers of different materials with different density, and are the result of careful research. When I did the research, I also contacted many manufacturers I could find of tatami floors and realized how few of these existed. I then also studied the alternative systems such as gymastics floors and cheerleading floors.
It was hard to share this with judoka because once again when you show the results and it shows that the floor they have or built is actually crap, they get angry. Judoka get angry all the time when you confront them with something they have or do and it shows it is not as great as they like to believe. At that point communication becomes impossible because rather than learning from that new language, their strategy often evolves to aiming at the person who did the research and attempting to isolate or discredit that person. At that point you start wonder what the heck one spends all this time for thinking that people will appreciate an learn from the new findings, when instead they don't want to learn. What they want is getting compliments that shows how wonderful everything is, which is not what I pursue in science. So all that really contributed to me deleting my post at the time.
In brief it showed that there is a big difference between what judoka often believe and science. That is because subjectively, some things are easy to perceive, but others are not. For example, you can easily perceive when a floors gives way. If you fall on your bed, it is obvious it gives way. But a bed would not be an ideal floor, because each time you move your foot, your foot sinks into the bed. To put it simple, there are many other scientific parameters that contribute towards the value of an optimal floor. Taking that into account, and considering all those parameters, the differences are tangible. There are all kinds of testing set-ups for this. There are several systems. There is no doubt that the gold standard is represented by the two systems that are the most complicated to build and the most expensive. Of these the steel-spring system is the most famous. My old dôjô had this, and it was amazing. Only few dôjô in the US have this. Sôkô joshi in San Francisco does, and the Seattle dôjô does too. It is also the system at the Kôdôkan. The system as it is in the Kôdôkan does not exist in virtually any dôjô in the West, the reason is that in Japan these systems are build into the ground, so they are sunk-in. In the West such a system is build up from the ground, but the mechanics are the same although the sunk-in system is aesthetically far more attractive. Today, people in the West typically quickly dismiss the system as too expensive and unrealistic. I think that this is nonsense. Most dôjô that have this system weren't loaded with money either and it was built by the jûdôka. We built it ourselves, well, not me, as it was before my time. But it requires a lot of work.
There is an even more modern system in Japan, but it is expensive, which instead of steel spring coils uses hydraulics. It is very elegant and the only downside being if such a hydraulic spring breaks of hydraulic fluid leaks. It requires professionals to build and install it. The steel spring coills are virtually indestructible, and their only downside really is that they make some noise, but that contributes to what I call the "dôjô sound" which is something very specific that some of the elderly jûdôka on this forum or those who have trained in Japan, I mean, real Japanese dôjô, not just the Kôdôkan, have experienced there. It is very special.
Only a few tatami manufacturers in the West also provide tatami flooring, but none of them --to the best of my knowledge-- still provides steel spring coil-based floors. The reason has to do with expense particularly in terms of man-hours. So, those who do, provide floors that are based on foam blocks or combined foam/rubber blocks. It is oftentimes an "acceptable alternative". However, do not understand this as me saying it makes no difference. Now, let's agree on some things to prevent this thread from turning ugly again. If you say that you have a foam block-based system and your dôjô and "that you like it and that it is really good", I cannot argue with that. If you are a fakir or a derwish and you say that your bed of nails is really comfortable and you like it, I cannot argue with that either. However, if you say that your foam block system is as good as a steel-spring system I will argue with that because it is nonsense. It may be true to how you personally feel, but it is not true in terms of comparison. The number achieved in various testing show up and expressed in many parameters other than what "you like and feel good about" do not leave any doubt.
But foam-block systems are much easier to built and cheaper. Over time they do lose some of their elasticity and some deterioration is anticipated. We do not know yet how much, because the system has not been long enough in use to have a data base.
Again going one step down, you have the tire-based system. Tire-based systems cannot compare with any of the above systems. The difference and lower quality is substantial and you can also easily perceive it yourself. Problems are unequal resilience, smell, particularly when it gets hot, not fire proof and potential problems with fire regulations, and others.
So, all in all if you want a relatively simple system, built quickly, that is OK but not outstanding, go for foam blocks. There is sufficient info on the net about these. If you go to a couple of manufacturers of gymnastics floors, you can find close-ups. Do realize that foam is not just foam. You need to carefully study what the density is the foam needs and how thick it is.
If you seek standards, there is one judo federation that has carefully written out tatami floor standards, and that, no surprise, is the most professionally run judo federation, the FFJDA or French judo federation. The standards say how the floor needs to be built and covers different standards. Logically, they are only available in French, not in English.