Yes, I know there are a thousand knee pain threads out there, but each incident is unique and specific, so I'm "consulting the oracle" (as my girlfriend calls BF) to see if anyone's had the same problem, and what their diagnosis and/or treatment was. I'm trying to ask specific
questions (not "my knee hurts, why?") to get specific answers.

Yesterday I was at about mile 55 of a 63 mile ride and felt what I thought was a muscle spasm starting, tried to ride it out for a couple miles, then finally got off to stretch (haven't had to get off my bike to stretch in years). The pain is on the inside, toward the back of the knee, just medial to the big tendon behind the knee. After stretching the pain subsided, but returned in a less severe form near the end of my ride. Now the morning after it is still tender if I make a "cycling motion" but doesn't hurt to run or jump.

I ride a lot - about 150 miles a week, but have just began integrating longer rides over 50 miles for the first time this season. The research I've done points to tendonitis, which I know is common among runners, but I don't know about cyclists. Any shared experiences with tendonitis would be appreciated.

(And don't refer me to the countless "knee pain" threads that don't contain specific information, thanks!!) I have to abandon the thread for a couple hours due to work, but bear with me, as this really sucks!

Sounds like iliotibial band syndrome (ITB) to me. Usual advice is to lower the saddle and spend a lot of time stretching. Some people have to take considerable time completely off the bike. For things like this, I usually combine ibuprofen with stretching and time off. I take 600mg ibuprofen twice a day for about a week, whether it hurts or not, also stretching twice a day. Then give the bike a try without Vit I, but ride easy.

And give Google a try.

I just found this website https://www.cptips.com/knee2.htm. Thought I'd post it for others looking for decent advice from a website that's not trying to sell something. To me it sounds likeMediopatellar plica syndrome or Pes anserine bursitis. I'm gonna try a short ride in the small chainring this evening to see what happens. I generally subcribe to MEAT treatment over RICE treatment if my injury is less than totally catastrophic, as I really can't fathom the idea of extended time off being a good thing except as I said in the case of a major injury. I have a feeling that tonight's ride will be telling.

I have also been raising my saddle incrementally as I had gotten used to it being on the low-side when I was rehabbing a back injury last season, so I think I'll drop it back down a touch.