A bit more clarification. Both bike setups are pretty vanilla. No fancy bells and whistles in regards to shoes and clips or other equipment. I usually wear a pair of track or low cut hiking shoes and go. I use a Garmin smartwatch and bike computer to track my activity on both bikes. Historically my pace is usually very close to 13 mph on flat to very gently rolling terrain. My road bike is obviously on pavement and my mountain bike is on hard packed old railway lines. I've never had any leg related issues in the past. Some time ago, pre COVID I used to ride regularly and never had an issue with shorter rides of 5-6 miles. The only time it occurred back then was when I extended out to 12 miles on a charity ride. It occurred at the end of that ride and I wrote it off to fatigue on longer distances. I just restarted cycling a month or so ago (just retired) and the first few times I was fine. But as I have continued on, tried to keep a standard pace, and have gently increased distance it has showed up again. I semi shrugged it off to a stamina issue and shortened distances to build myself back up again. But the knee issue is only thing that occurs. After riding yesterday, with numbness occurring, my legs muscles just below my knees are comfortably sore today from the ride as expected, but fine everywhere else. Lower/upper legs, butt, back, hands, and arms are fine. I'm thinking blood circulation is not happening as it should to my knees and maybe raising my seat a wee bit to insure legs are stretching out. Going to contact my bike shop to see what they say and maybe schedule a refitting. I might also contact my Dr. and/or visit a sports medicine clinic to see what they say. Thanks to all for advise.....appreciate it.