causes your legs to get bigger?

Hello, Mine got skinnier. Now, I have a lot of trouble finding knee highs that stay up! My mother-in-law's thighs got thinner/firmer too.

If your legs/thighs have excess fat on them, you should expect them to get thinner while losing the fat, your muscles are being toned but the loss of fat is what is noticable. If you are on a stationary bike for fitness/weight loss and your legs are skinny, the bike will help tone and shape the muscles. The stationary bike should not cause your leg muscles to get that big unless you start training like you are trying for the cycling team at the next olympics.

I have not had that problem - in fact, my bike helped me slim down my legs. Sure, you build muscle, but it's definitely smaller than fat!