I hadn't been going to practice very often for one reason or another, but I had been going to the gym quite frequently, and lifting pretty heavy weights with my legs. I recently changed gyms and my new gym has a squat machine that is a bit too small for me - even on the furthest seat setting, I have to start from a very tight squat position and I could feel that it was putting stress on my knee. One day, I felt a "twinge" in my left knee, but it didn't hurt so much that I stopped.
Then, I went to Jodo. I don't usually warm up much before jodo, because we do Kihon and warm up "naturally". But on this particular day, I jumped right into koryu and was trying to do Neya no Uchi. I wasn't popping up strongly enough, so I was being told to go from a one-knee position, to a straight-legged "ready to go" posture. I didn't have much luck with that - my legs just aren't strong enough to launch me forward like that.
The next day, my left knee was really hurting me, especially when going up stairs and in particular when my knee straightened out. It still hurts, in fact.
So, I have been trying to do a self-diagnosis using information on the internet. I should go to the doctor, but ... simper simper ... I don't know if I have coverage for this kind of thing, it's hard to get time off work, it doesn't hurt THAT much, maybe I should just rest it for a while, etc.
In the meantime, I am taking a break from iaido, at least. I think my left knee is worse than my right knee as a direct result of tate-hiza always being done on the left side.
Anyway, anybody have any experience with this kind of pain: short, sharp pain inside the knee, very centralized, occurs when you straighten the knee out when it is bearing weight?