It depends how much resistance you have on the machine. If it is set quite light, you will tone-up and increase your stamina. If you wanted to build muscle, you would increase the resistance.
No, dont worrie about it.. I have been doing it for years and my legs are small and lean. people allways tell me they wish they had my legs.. GIVER ON THEM haha
Cardio gives your muscles a long lean look.. If you want to build muscle you have to be doing weight training.. Yes you get muscles from running (and cardio machines).. you get very nice ones.. And it is very hard for a women to get big and bulky because we only produce a very tiny amount of testostrone... I run and bike very hard 5-6 days a week and I also do heavy weight training 4-5 days a week and I have for years.. I can lift ALOT of weight but I am a small person. Im 5.4 tall and 120-125 lbs.. Trust me if it was easy for a girl to be big and bulky I would be there already.. Im lean and small.. with toned muscles.. and Im proud of that.. You go and WORK IT GIRL!!! jen