Spinning leads to bulky thighs in girls?

Spinning won't make you look bulky, it also won't 'tone' your leg muscles since that is a made up thing.

Spinning will help you lose some weight and will increase your cardio capability.

If you want to get sexy slim legs the bes thing to do is to lift heavy. It will drop your bodyfat whilst giving you hard and shapely muscles.

you don't need to worry about gaining bulk unless you eat loads and take supliments.

"I often tell my students “Your butt is your engine!” to emphasize that power comes from hamstrings and quads. The spinning system is certainly lower body-focused, and it is a common misconception that resistance builds bulk. However, resistance is chiefly used to engage the leg muscle, stabilize bodyweight, and prevent injury. My dear resistaphobes, please take note!"
- See more at: http://sweat.burnthis.com/health-questions/does-high-resistance-on-spinning-bikes-leads-to-thunder-thighs#sthash.qt9fMmpu.dpuf

Of course, anything with resistance is going to build muscle - or at least maintain it.

I would think you'd be limited on how much you build by the amount of protein you are consuming.

I waffle on this one. I'm not a spinning fan (my butt doesn't like the saddle), but I've seen people have amazing weight loss results while doing it. I have heard you don't build muscle while eating at a deficit, so resistance is to maintain the muscles you have.

... standing on medium to high resistance / up hill spinning for nice tight calves (and to avoid a sore bum!)!

I have been spinning for many years and it is a great cardio workout. I don't agree with other posters that it will not build strength - the tension and amount of the "out of the saddle work" will result in muscle gains if you work hard (I do). Seating there with light tension and minimal effort (i.e. ignoring the instructor) will not get you far. That said, I couldn't agree more that lifting is great and it a much more efficient way of gaining strength. I have also been doing this for years and in recent few months I have been doing heavier lifting with a lot of squats, glut thrusts, deadlifts etc. with progressively higher weights. My legs are getting stronger and gaining much more definition - bulking no. I would never recommend that anyone just do spinning, particularly since it doesn't do anything for the upper body. Mixing it up is always good, particularly if just doing the same type of work out will result in you working out less overall.

I for one have NEVER seen a serious biker or spinning class addict with big thighs.

<<< My thighs... I teach spin and also ride quite a bit... From Spring to fall I rarely lift lower body, I just climb more. Fast flats with little tension is good for cardio, but won't do much for the legs. Climbing and tension can tighten things up... My thighs are quite toned, but not huge. You can browse my profile pics if you'd like.