You should only be breathing hard if you're doing speedwork. For a normal run you should be able to carry on a conversation or sing a song without gasping for breath. If you're gasping you're gonig to fast. Just because you're legs can keep up the pace, doesn't mean your lungs are ready. They need training too.
It's funny this has gotten so much traction and yet the OP hasn't checked in since shortly after posting the question in Oct. 2013. But for the sake of those that stumble upon this searching the forum, or clicking on links in Active.com emails, if I were the OP, I'd look at the general consensus of all the replies and slow down. From the sounds of it, you didn't have much of a prior history running, so you're going to have to build up to it. Just the way it is. If you were previously a runner, you can't jump back into cardiovascular activity and expect to pick up where you left off. And if your PT actually helped you maintain your cardio base, getting back out and running is a whole different animal and will take some adapting.
It's one of the hardest things for new runners to do, pace themselves. Get a heart rate monitor if you really feel lost, or you feel a disconnect between speed and level of exertion. The biofeedback provided by getting a sense of your heart rate while you train will help. Calculate your zones and stay in the lower aerobic range for a while (like months). And honestly, maybe I'm being an alarmist, I don't know how intense your PT was, but if you are consistently feeling lightheaded, go get a checkup with your GP and make sure you're all good to start an exercise routine. As a matter of fact, if you're just embarking on incorporating exercise into your daily routine, it's not a bad idea to get that baseline health check from your doc before you begin. Imagine how awesome it will feel, when you go back in 6 to 12 months and he/she tells you how great all your test results look! (Speaking of which, it's been 3 months since you posted. How are things going??)
As for breathing and form:
Finally, you say you are doing a Couch to 5K. One would assume that means you are following a training program. That structure is important and will help you build towards your goal in a controlled, safe way. If you don't have a plan yet, there are tons of apps that can guide you through training and set a schedule for you. When I started running again after many years off, I used some of the free training plans on RunKeeper for iPhone and really enjoyed it. I particularly liked the 10K+ plans by Jeff Gaudette, but started with Mike Deibler's R4FL program. I've also heard great things about Jeff Gallaway's Run/Walk approach, but his plans on RK involve a fee. Though you can learn about his approach and practice the principles on your own. I still maintain a training log on RunKeeper, (as well as other sites), and it's been great to track my progress.
Hope you check in again and let us know how things are working out.
Similar problem....I think it is solved easily by concentrating on breathing through your nose and not your mouth. I believe the problem you describe is caused by a lack of O2 because your are breathing through your mouth and quickly depriving your body of the oxygine it needs.
Practice inhaling throug your nose and exhaling through your mouth and I bet this will make a world of difference.
Many of us, myself included, simply cannot get enough air through the nose to keep running for long, or, for me, any kind of normal running pace. And why should I inhale through the nose but exhale through the mouth? It is pretty clear that your mouth allows a larger volume of air on inhale and exhale.
This is the exact issue..you will never get as much 02 into your lungs inhaling constantly thru your mouth v. your nose.
it's easily confirmed..when you are tired, inhale big time thru your nose several times...you will be able to tell the effect on you immediately,,whenever you feel tight/tired after running for a time, inhale big time thru your nose several times..you will get an immediate benefit that allows you to keep going more comfortably..
if you do one lap around a track and inhale thru your nose just 10 times during that lap,,you will be amazed by the positive effect v. if you didnt.
The only folks who advocate this nonsense about inhaling through the nose aren't really runners. The fact is, the nose is only capable of providing a fraction of the air necessary for most runners in most running situations. If someone is having breathing problems, the universal way to solve the issue is to slow down.
Fat old man PRs:
I can vouch for the effectiveness of the techinque that lenzlaw mentioned. I am not an expert runner but I consider myself pretty good for my weight. I'm 5'10" and my body likes to be around 200 lbs when I am at my most fit. I am a Marined and even when I weigh as much as 220 at 31 years old I can out run alot of the younger Marines in our fitness tests. My best time so far has been 20:41 on the three mile run and my goal is to beat 20 minutes.
One thing that helps me is my breathing control. I've never seen the article in Runners World, I actually started doing this about 6 years ago when I started running more. I had been doing yoga for a few months and I noticed that my lung capacity seemed like it had increased and I could hold my breath much longer. Then I remembered something from Anatomy class in high school, we generaly use only a small amount of the oxygen we breathe in. My thought was, if I leave the air in my lungs longer then maybe they will be able to exchange oxygen and carbondioxide more efficiently.
My body seems to respond very well to the three in two out method. But, I'll adjust my breathing depending on how i'm feeling or sometimes just let it do whatever because it can take alot of concentration to maintain it and sometimes my mind like to wander while I'm running. It does get easier though the more you practice.
There have been times when I wasn't keeping strict controll over my breathing and I felt side stiches coming on durring a run. When this happens I force myself to breathe as deep as I can, hold it for a step or two and breathe it out as fast as I can. I'll continue that untill the pain goes away. It usually works without having to slow down much if at all.
I also believe it can help your legs stay fresh longer into a run. If your muscles aren't getting enough oxygen they'll switch to anerobic energy conversion(at least this is how I understand it so if anyone knows better please let me know). Anerobic conversion is less efficent than aerobic conversion and also creates more lactic acid.
That all being said, I also agree that you don't need to push yourself to the point where you need that technique on every run. But It might help you on those days when you just want to let your legs go wild.
I only started running in Jan this year and I also had trouble with breathing issues. I also went onto forums and asked the question and received a lot of feedback with help. Most of the feedback I received was to 'slow down' although I already thought that my speed was slow enough. My PB up until 2 weeks ago was 3.5km and i was struggling to breath which had impacts on my distance. Then my breathing was in through my nose and out through my mouth.
2 weeks ago I went running with a friend and her personal trainer came with us. The personal trainer kept saying to my friend 'make sure you control your breathing'. I had no idea what that meant. So i asked this PT what do you mean by controlling your breathing and I told her i didnt think i was breathing correctly. She told me that if i was breathing through my nose and out through my mouth, ofcourse that would cause issues. She told me to only breath in and out through my mouth and then 500m down the road pick a spot and then take in a large breath through your nose and out through your mouth and then continue with breaths only through your mouth.
I didnt think much of it until I tried it. It works for me! In that run i did 2 weeks ago with my friend and her PT i smashed my personal best that night by doing 5km without realising it. I again used this technique last week for the Melbourne Australia Colour Run 5km and it worked again. Last nighti did 5km and used the same breathing technique and i was able to complete 5km again.
Another tip she taught me was when i get stitches, take deep breaths through the nose and out through your mouth and it will disappear shortly.
I hope my input helps you with your breathing difficulties!