Before you freak out, take a
deep breath and understand what is probably going on.
Most women are so concerned about bulking up, especially their legs, that they UNDERplay their leg routines especially with weights. That means, let's say your circumference measurement of your thigh was 20 inches but didn't contain much muscle, mostly fat. It's still 20 inches but the soft fat is pliable and gets very easily squished into tight jeans or pantyhose and can be artificially squeezed into something smaller (ie: that compression of fat is what tight pants, jeans, and hose do).
However, when you FIRM UP, and you begin to remove some of that fat and put on lean
muscle tissue, two things happen. At first some displacement takes place where the muscle pushes out a little bit of that fat, AT FIRST. It's VERY temporary because that muscle "eats away at" that fat for energy. What's left is a SHAPELY thigh, that's firm.
However, what also happens is muscle is firm and hard and shapely and the same 20 inches of thigh can NOT be squished like a fatty thigh into tight compressive garments. This makes you FEEL like you're bigger because now you can't get away with squishing the fat up through the hose the same way or up into the jeans.
Fat on thighs gets moved along up and down, around the leg, with very little muscle to support it. But fat is pliable, so it's also deceptive. As soon as you take off any "support" type garments like hose and jeans, it all falls back down.
I know this because I've seen it and because it happened to me. It's a mis-perception and a mis-conception of what's happening.
Unless you are that rare fraction of a percent of females who truly "bulk up" -- this IS what happens.
Men have over 20 times more testosterone in their bodies (and in the morning, they have a hundred times more circulating their blood streams).... WE as women just do NOT have the capacity to bulk up naturally. We just can't.
Even those of us females on here who WANT to, who TRY to, who EAT and LIFT and WORK very intentionally to, we fight for every 1/4 inch we gain with buckets of sweat.
If you did "jazzercize" or lots of cardio before without "bulking up" it's probably because you ate away at all your muscle with all that cardio and that left your thighs fatter, not with muscle.
This muscle will raise your metabolism and give you shape and you are not bulking up,....really.