I hope this isn't a stupid question!  I really love running and I've been doing it seriously for about a year (5-10 miles at a time and the occasional half-marathon).  Over the past few months I've noticed a lot of muscle developing in my inner-thighs and I don't like it.  I've been told that adjusting speed or doing intervals can affect which muscles I use but I don't know how that works.  I'm okay with my calves getting bigger, and I already run on my toes.  Any thoughts on how to avoid further bulk on my thighs?  I've thought about taking a break from running altogether but I'm afraid the alternative won't burn as many calories,  leading to weight gain.  Suggestions?