peripatetic

This is my first post in this particular forum.

I recently took up biking, mainly for transportation in the city. I was riding fixed at a low gear for awhile, but then my bike plopped out on me, so I switched to an old 80s 12-speed.

Last year, I trained for and ran a half marathon in probably too short a period (about two weeks.) However, as a former cross-country/track runner, I felt confident in my approach, and didn't think I had pushed it too hard. Then winter came and I stopped running, but started riding the fixie. Sometime soon after the bike, I began to suffer slight and infrequent twinging pain in my left (non-dominant) knee. I'm 33, also former habitual tennis player, and this was the first knee pain I'd ever experienced. Did some research and came to the conclusion that this was a case of 'runner's knee'--patellar tendonitis--and that it had come from overtraining for the half marathon. I decided to lay off the knee, though I continued biking a bit. The knee pain persisted, though, and the negative pedaling involved in fixie riding seemed to exacerbate it, so I then switched to the road bike and generally lessened the biking. The pain lessened in frequency, but still seemed to be lingering. In the past couple of weeks, I didn't bike much at all, and my legs were feeling esp. fatigued.

Anyway, yesterday, I went out on a long ride in hot, humid conditions with a friend. She and I went about 20-25 miles, which was probably about 15 more than I had done in a looong time. My legs felt great during the ride, though, esp. going up some long but not-too-steep hills.

When I got back, for the first time in over a month, my legs felt fantastic, and I didn't feel any knee pain. They were tired last night, but not today.

I have a few short questions:

1. Is it a good sign that I don't have any knee pain today, or is this just a false promise? I came to the conclusion yesterday that part of the pain and general leg fatigue was coming from all the walking on pavement that I have to do here in NYC. With relatively flat feet, I definitely think that this has been hard on my legs. But still, if I just sit around for a day, my knee still hurts.

2. If this is a good sign, why? I know the basic idea behind therapeutic approaches to patellar tendonitis, and I know that biking is supposed to be good for strengthening the muscle groups around the patella, but still, I'm wondering how merely one day of challenging riding actually helps the pain to go away that quickly.

3. If it's a good sign, should I keep doing these longer, challenging rides? How much riding is a good, healthy amount over the course of a week? What do most serious riders consider enough to keep in good shape/form? Anyone out there rehabbed a knee through biking? What did you do?

BTW, I'm a skinny 5'9" and as I said before, 33 (male.) Any insight people might have out there would be much appreciated.

Thanks for reading my longwinded post,

max