The minimum lengths and weights of shinai for various divisions are specified in the official Match Regulations. Shinai will always be checked before major competitions so it’s definitely in your best interest to make sure it makes the grade beforehand! It’s hard to beat an opponent if all of your shinai are disqualified.
In the case of small children, shinai must be of a manageable length and weight for each child. There are no rules as such. The rule of thumb, however, is one that measures from the floor up to the child’s armpit.
Remember that these official weights are WITHOUT the tsuba attached. Although the rules must be abided by in official matches you are free to use a lighter or shorter shinai in training just as long as it is safe. Depending on the training you are engaged in a lighter shinai may be a better option for learning new waza. Beginners will have difficulty performing correct movements with a heavy shinai. Suburi, for example is an exercise in which some people opt to use a heavier shinai, but a beginner risks developing bad habits through unnecessary tension in the shoulders and arms. Sticking to regulation weight is probably best here. For more advanced practitioners, using heavier-than-regulation shinai is a good way to build endurance and shinai control.
As for choosing a shinai at the shop, this is very much a matter of what feels right to you. And, what feels right to you will change over time. I can’t count the number of times my shinai preference has changed over the years. Starting with regulation weight then opting for thinner shaped shinai, massive heavy logs, oval grips, hand-heavy weight, tip-heavy weight… I seem to have come full circle now and prefer regulation weight with thinner tsuka.
In any case, let me share a few tips I learned for choosing a shinai that will/should last. If at all possible, I look for Matake shinai for starters. “Matake” means that it has been grown in Japan, and although nature dictates that there are many exceptions to the rule, generally speaking the fibres in Matake are more compact and hence durable. This has something to do with the climate in which the bamboo is grown. It is, for the most part, stronger than the bamboo grown in other parts of the world like China or Taiwan. Which is, incidentally, where most of the shinai sold in Japan and the rest of the world are actually made.
Matake tends to splinter with use and only requires a bit of filing and sanding. Careful maintenance will keep it working for you for a long(er) time. Other bamboo tends to split outright which means goodbye slat. No maintenance possible here, but you can save the good ones and make Frankenstein shinai. Not ideal, but still very usable if the orphaned slats are all from a similar shaped shinai.
Anyway, once I have found one that feels right in terms of balance, I weigh it on the scale mentally adding the extra 30-grams or so that the leather fittings attached later weigh. Then, I hold the shinai up to the light so that it reflects up the length of the top slat, slowly turning it around to check each one. What am I looking for? Marks or indentations running across the width of the slats. If they are there, the light reveals them. If the slat has what looks like faint ladder rungs in any section of the bamboo, I put it straight back in the rack. These barely noticeable marks are the result of forcing the bamboo slat into shape. This tends to damage the fibres of the bamboo, hence the slight indentations. It doesn’t take a rocket scientist to deduce that bamboo damaged in the production stage won’t give you bang for your buck in mortal combat on the dojo floor.
It’s only a little thing, but 30 years and hundreds of purchased shinai has shown me that its important enough to look for. Of course, if you’re buying online you don’t have many choices, and it becomes a bit of a lottery with what you get.
Editorial note: You can click the "Alex's Blog" tag below to view his other ones, including related topics like how to take care of that new shinai you just bought.
So what do you guys think? What are you looking for when you shop for shinai? Any advice you'd share or some tips you have?