I have a mountain bike with semi-slicks. I've been doing all city street riding....nice smooth surfaces. I've been measured for my bike. I have proper leg extension, comfortable back position, and can probably ride an hour without any problems.

However, once I stop riding, I get pain in my knee joints. I only started riding about a week ago. Prior to that it was about 25 years since I last rode.

Any suggestions as to why I'm getting the knee pain?