Does running build leg muscles? I'm a beginner and my legs give out before I'm out of breath while I'm running. During this time that my legs are hurting am I building some kind of muscle in there? Where is that pain coming from if it's not a muscular thing going on?

Even if your cardio system is ready your legs/ligaments/muscles have to build up the tolerance for all that pounding. Most people are stiff and sore the first few weeks as it's a big adjustment for the body. Not only will your legs feel it but likely your core too.

Yes, it does build muscles to a degree, if your legs aren't very muscular. Most people will say most runners are mostly lean and it's not muscle building... but most people notice some muscular difference the first few months. This has been my experience. My legs have never been more solid (well under my fat anyway!)

Give it time, Don't overdo it (start off with short runs and work your way up) make sure you're wearing proper shoes, run on softer surfaces to begin with, and give it a few weeks and you'll probably be more comfortable.

PS - If you want to work on your cardio and feel your lungs can handle more then your legs a good way to get extra time in to keep building your cardio is to walk on incline on the treadmill. Gets your heart rate up fairly close to what it might be running without being so harsh on the legs.

If your legs are giving out try some leg training on your off days of running, squats, lunges, leg extensions, to strengthen your leg muscles, ligaments and joints....

more than likely ( in myopinion/experience) what your feeling when your legs are "giving out" is the lactic acid thats built up as you are running! Because you are a beginner, and you are probably maintaining a relatively high effort, cardiovascularly speaking, its going to build up pretty quickly, and once again, because you are new, your body just cant process it out as fast. That takes time for your body to learn how to do! On the plus side, your cardiovascular system will improve much more rapidly and noticably, which WILL delay the build up of the lactic acid!

Also, it takes time for your muscular/skeletal system to adjust to the pounding and impact of running. That will get better pretty quickly too!!

I spent a lot of time with my trainer working on building my leg muscles and muscles that support the knees before I took on running in a serious way. Even still my cardio will outrun my legs any day of the week (I have slowly over many months built up to running 22K on my long run days).

Like others have said don't take on too much too fast - start out with shorter distances and build - you'll be surprised how quickly you are able to add distance and your body adjusts! It's a great feeling!

Two words: Heck. Yes.

My legs are the most muscular part of my body thanks to running!

I took a full 4 months of building up my leg muscles before I attempted running. I've always had issues with my knees and I wanted to be sure my knees could support my weight. I got down to 180 before I allowed myself to run, so I understand what you're saying.

I hope you guys are right, My thighs are my biggest problem area and I'm hoping running will slim them down.

I'm pretty sure once your body fat goes down, your legs will look awesome

you bet your thighs will slim down! I have the same problem area and they are getting to be a very nice shape. They're still not tiny (and never will be) but they're toned looking.