On the leg thing, maybe you're in too high a gear? Try one or two gears lower, and make up the speed by increasing the cadence.
If you're using a platform pedal, you could (and should) go to clipless or Power Grips. Being able to lift the pedals on the upstroke will make a noticeable decrease on the opposite muscles.
If your seat height is right, and you've already tried all the rest, maybe you're just trying to progress to quickly.
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Some people are like a Slinky ... not really good for anything, but you still can't help but smile when you shove them down the stairs.