I've had knee problems for 30+ years. Many surgeries, then my left knee was replaced back in 2009. Right hip replaced in 2011. Been through a *lot* of PT. Am not any kind of doctor. But after my knee replacement we found that one muscle (or a part of one muscle) was not even building tension as it should. The PT DR gave me some 8-11 different exercises just to help bring back my left knee. Sure, riding a stationary bike will help, but that can be more about overall strength and cardio, than about the 'quads' themselves.

As I am only a guy with bad knees, and not a PT DR, I can't tell you the *best* ways to strengthen your quads like a DR could, and going to a good one would be my best advice. That said, many exercises can be done from a chair, the floor, or your bed. Straight leg lifts, lift and hold, squeezing and holding the quads, and much more of the same... learning to simply tighten the quads alone takes practice for many people.

I can not (nor should others) tell you what exercises are correct for *you*, and if you start doing the wrong ones for *you*, you can hurt yourself.

An 'elliptical machine', doing 'squats', stair-stepping, just to name a few *can* do wonders for both the quads and upper leg muscles. A stationary bike is boring as hell if you've not spent 30 minutes daily for a year on one...actual hill climbing while riding is great for both cardio and leg muscles - but again, doing stuff willy-nilly - you could hurt yourself badly, and possibly do damage to your knees. This is why seeing a PT Doc is a great idea.

Good luck to you