My experiences is that you don't have to bulk up with running, although I suspect muscular thighs are about par for the course. Although this is actually good in the long run - my dad ran a LOT as a young adult and he still has really young looking legs compared to most of his friends because they're still muscular!
My advice is to do something like the strength work in the Tracey Anderson method (not the cardio, which you get from running, or her diet which is to me INSANE) which engages your secondary muscles rather than exercising all the big ones (like free weights would) because that allows you to get stronger, and better at running, but doesn't seem to bulk you up. I've been using her 30day book/dvd for about 3 months a couple of days a week, which is not at all how she says to use it, but it has really helped.
Also, bulking up in girls who exercise is associated with excessive cortisol production, which might be happening if your workout is stressing you out! Your body releases it when you're stressed. So if you run fast, try slowing down a bit, don't increase your distance by more than 10 percent in any given week and slow right right down when you get things like stitch until it goes away. And don't run around fretting about how well you're running!!
I'm a runner! For almost a decade now. I do, of course, participate in other sports, but I identify most with the 'runner' tag. I like outdoors and I like treadmill. I do races, 5k 10k and half-marathon, with (as of now) no desire to take on a full marathon. That may change, but somehow I doubt it. I ran my first half at exactly 4 months postpartum, strict vegetarian. Just started trail running this year, did my first trail half in May, and actually did 5 trail miles this morning. I find that the vegan diet lends itself well to energy levels and sustaining that kind of strenuous activity for so long. My pre-race tradition is pbj on whole wheat bread. It sits well on my stomach (meaning no surprise porta-potty stops) and it lasts a long time, so I don't normally need gu or anything like that during longer runs.
What about hydration? I use gatorade but would like to get to the point where I just use water but it is so tough. I run near the equator and it gets really hot and humid. I drink lots of water but don't feel thirsty until I drink gatorade. Any advice?
NEVER drink gatorade! all those energy drinks have tons of unhealthy sugars which counter effect your hydration! Try coconut water,I swear by it! It has tons of electrolytes,which you lose during exercise and sweating as well as living near the equator.I live in Hawai'i,and every day I return from a long round of work,classes,exercise outdoors,I drink some and it really helps me combat the dehydration. Vitacoco is my favorite brand.
I ran for an hour today! It has been over a month.I was traveling a lot so I walked a lot,did my yoga and weights..and was able to hike every day for several hours.So I am definitely in shape for it,just need to stay out of the horrible pitfall of humidity temperature hours: before 10 and after 5!