Breathing is key to getting oxygen into your body! Your body ultimately uses it to ‘burn’ the energy stores (carbs) in your body to produce energy.
If you are finding it really hard to breath then, simply, you are probably running too fast. Slow down. Most of you reading this article will be beginner runners and therefore you should be focusing on distance work at a speed where you can maintain a conversation. By definition breathing will not be difficult at this speed.
For the more advanced runner then consider the following:
1. your mouth is bigger than your nose. So use it to breathe.
2. A large amount of the capacity of your lungs are not used. Therefore it probably doesn’t matter too much what you are doing.
3. Breathing is mostly subconscious. Get it right and it becomes natural. Personally I’d breathe in over the count of a couple of footfalls and then out over a couple. Get into a rhythm.
- What forces a person to take a breath(wiki.answers.com)