Originally Posted by JerrySTL

You shouldn't be mashing the higher gears to build muscle. What you should be doing as spinning the pedals at somewhere between 75-95 rpm. It's much better on your knees and will build up the correct fast twitch muscles that are best for cycling. Once you start spinning, instead of mashing, the pedals, your average speed will go up and your knees will thank you.

You paid a lot of money for all those gears. Use them properly and shift often.

Originally Posted by MRT2

Take a few days to a week off and see if the pain goes away. If the pain does not go away, see a doctor as you may have torn something (ligament, tendons, cartilage). Hopefully though, it is just a strain from overuse or mashing in too big a gear. I concur with JerrySTL's advice about spinning, rather than mashing the pedals. Except for climbing hills, which you say you don't do, cycling is an aerobic activity. Finally, maybe consider cutting back on cycling and adding some other activity, like weights, yoga, or swimming to your workout schedule.

Originally Posted by Kindaslow

Focus on spinning. "Our" knees often do not hold up well to certain pressures, like trying to build muscle via mashing. Also, the slower you lose the weight (maintaining reasonable weight loss) the more likely you will stick with your plan. But, if you blow out your knee, it will be very difficult to continue.