I am not for a moment going to try to explain the relationship between kendo and zen. To attempt to do so would take me way beyond my own level of understanding. This is more me musing on the different levels of emphasis placed on that relationship by different kendoka.
Along with kyudo, sado, shodo and ikebana to name a few, all of the Japanese sword arts have a strong zen tradition. The various aims of heihoshin (natural mind), fudoshin (immovable mind) and munen muso(no intention no mind) are integral concepts and goals of kendo practice. Kendo however is loud and visibly aggressive and does not tipify the serenity of say, kyudo. This, I believe, makes for a population of kendoka who’s interest in zen ranges from zero to intense.
Whilst kendo has developed around an underlying zen philosophy its concepts could be applied to any other sport. A six in cricket, a baseball home run, a horse and rider clearing a big fence or a Jonny Wilkinson drop goal are all probably achieved in the same spirit of mushin as the perfect men attack, but it is unlikely that the conversation in the post match dressing room will cover satori.
I find it strange, if after years of a practice, a kendoka has no interest in reigi or the theory of kendo, but it is more disconcerting if someone takes up kendo with a religious fervour or belief that they are there for instant enlightenment. It is easy to talk about zen concepts, but without long hard training there is no chance that you will really understand how they apply to kendo.
Through continued kendo practice, people certainly achieve moments of clarity and for me it is the perfect way to continue to exercise my body whilst occasionally feeling that I am becoming to understand myself better than I did a few years ago. However if you are looking for instant dharma, skip the kendo and go straight to the zazen.