I'm 60 years old. I ride a Trek FX-2. I only ride about once a week for 20-30 miles. Usually when I get close to about 20 miles my right knee starts to get sore. If I stand up and pedal it will temporarily go away but comes back within minutes. It is a bit like a grinding sensation. I spent about 40 years milking cows with a lot of ups and downs from a kneeling position. Does anyone have any recommendations or any exercises that might help me avoid this problem. Thanks.