I am often asked whether I would recommend other ways of training outside the dojo to improve kendo. Firstly, I should make it clear that there are people far more qualified than I to advise on this. Sports scientists whom I know have done work in this area are Steve Bishop of Edinburgh University, Ian Parker-Dodd of Gloucester University and Honda Sotaro of Fukuoka Kyoiku Daigaku. If any of you see this please comment, but for the moment this is my personal kendo-centric view of the subject.
I originally took the view that kendo training was sufficient in itself to build the stamina and muscle development necessary for kendo, even though I was used to the regular sight of Japanese high school and university kendo clubs out jogging. I was recently reminiscing about shared memories with an Osaka kendoka who mentioned that his sensei would make the class run several kilometres from their high school to the shudokan, before putting them through a very tough keiko session. Nevertheless, I have been to numerous adult kendo sessions where warming-up for some of the high-grades consisted of a cup of green tea and a cigarette.
With hindsight, this was probably based on the fact that they had done the hard work at an earlier stage of their kendo careers and they were relying on a mix of indomitable spirit and refined technique to put the rest of us under pressure.
I currently practice kendo a minimum of three times a week and whilst I always join in with the kihon, and work on my own kendo as well as acting as motodachi in keiko, I do not get as out of puff as I used to. This is either because I am under less pressure now than when I was lower in the grading structure or because I do try to work on stamina outside the dojo.
I have taken to visiting my local gym two or three times per week and spend an hour + on cardiovascular exercise before using the weight machines for a fairly low weight / high rep workout. Although I much prefer kendo, the challenge of increasing the length or pace of a workout is enough to keep me interested and I can always watch TV from my treadmill.