One of the most vital yet underrated areas that you can work on to improve your running efficiency is to correct a faulty breathing technique. The problem is that many people breathe from their chest rather than from their abdominal region while they run. Abdominal, or belly breathing, is the best method to inhale air deep into your lungs where most of the gas exchange between oxygen and carbon monoxide occurs.
Whether you're a beginner or an experienced runner, take the time to learn and employ the abdominal breathing method. As a minimum, just remember to keep breathing deeply and regularly. In most cases your breathing will take care of itself; as you run faster, you'll breathe faster.
And yes, most runners are mouth-breathers or at least nose-and-mouth breathers. It would be impossible to take in adequate oxygen by breathing only through your nose.
A secret to breathing better when you run is to remember to put a little more force into your exhalation. Your body will naturally inhale to make up for this, which in turn will improve your breathing efficiency.
Establishing Your Breathing Rhythm
Your breathing rhythm is an important component of efficient and complete gas exchange in your lungs. Rhythm and stride are closely related to your breathing, so it is natural to learn to synchronize your stride with your breathing as you learn proper biomechanics.
Your breathing shouldn't be labored. If you find yourself huffing and puffing, you are probably running too fast for your current level of fitness. Run at a pace where you can speak comfortably in complete sentences. In other words, your pace should be such that you're not gasping for air after each couple of words.
Whether you take three strides for every breath or two, your breathing and your stride are probably in sync naturally. Beginning runners, though, make the mistake of breathing at a 1:1 rate. This means that they are taking one step while breathing in and the next step while breathing out. This essentially is panting, and it is inefficient breathing.
A more economical way to breathe depends, to a large degree, on the pace at which you are running. For your average run, you should breathe 2:2—taking two steps for every breath in and two steps for every breath out—or 3:3 for longer, slower runs. As you run faster, you may have to breathe more often, which leads to such variations as 2:1 and 1:2 patterns.