Does bicycling give you toned smaller legs?

I have a membership at Bally Total fitness - I just got it 4 weeks ago. I am going to get more serious with my eating and exercise routine. Theres this thing called "reaction cycling" - what you do is go on a stationary bycicle for ONE HOUR and you do different postions and techniques on the bycicle. Theres an insructor telling you what to do. When people get out they are so tired and sweaty. If I do this 3-5 times a week with a good eating plan will my legs/thighs slim down?