The other day a visitor at the dojo asked me about kiza and if it would ever stop hurting. My honest reply about the last part was, “I sure hope so!” Timing people at the All-Japan taikai I found that if all goes normally you need to be able to sit that way for about 3:30 per arrow. Of course it depends on where you are in the sequence of five. The waiting time for the otoya is roughly the same everyone, about 3:00, but the waiting time for haya varies from nothing (o-mae) to 3:30 (ochi). But if something goes wrong — a broken string or a dropped arrow — or if you happen to be behind one of those people who linger for an eternity in kai, it’s safer to be able to sit like that for five minutes or so. There is this excruciating video.
So how to manage? The main suggestion I’ve found helpful was just to get used to it by sitting in kiza every day for as long as it is easily manageable, gradually extending that duration as the weeks and months go by. As with any kind of stretching, the fastest way to make progress is to go slow. You want to avoid an injury that would force you to halt your stretching regimen while you recover, and so have to start all over again from the beginning. So, the pain is your friend, telling you when to stop. The one auxiliary suggestion I have for this is to try it in the bathtub after you’ve soaked in hot water for a while. This is easy in most Japanese homes, but in “shower countries” I’m not so sure. The heat will relax the muscles, and buoyancy will reduce the strain, but be careful not to overstretch.
The other thing that helps is to do some exercises to strengthen the quadriceps. The main problem I have in kiza is that one of the muscles of the lower leg, the extensor hallucis longus, is overstretched and after a few minutes can start to spasm. This causes the foot (especially the big toe) to extend, which pushes me forward, and if that continues for too long there is a point of no return where, if I haven’t been able to stand up, I’ll fall forward with a thud into seiza. Ha! This can be avoided by keeping one knee “alive” (the ikasu condition), but that, in turn, requires stamina in the quadriceps.
But if all else fails, and you have to do it unprepared, just keep in mind that the ability to endure (gaman) is one of the highest virtues in Japanese culture, and it will be appreciated, sometimes in surprising ways.