Does spinning cause big thighs?

I think over a long period of time there could be some muscle gain in your thighs through aggressive and repetitive spinning.  If you look at most competitive cyclists, my point will be proven.  Cycling, as well as spinning, can place high resistance levels on your thighs.  In spinning you control the resistance, therefore my conclusion is you’re not using high resistance and you’re not spinning repetitively, your chances of increasing the size of your thighs is very limited.