The following is a basic breath retraining exercise taken from Asthma Free Naturally
Step One: Become very aware of your breathing. Feel, watch and listen to your breathing as much as you can during the day, paying particular attention to what causes you to take big breaths.
Step Two: Learn to breathe through your nose and do this at all times. The book contains an effective exercise for unblocking the nose in a matter of minutes.
Step Three: Breath less, this is the very essence of Buteyko breathing. Remember that "over breathing" will trigger asthma and the intention is to learn to breathe a more correct volume by relaxation.
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Breathing can primarily be reduced by relaxing all of the muscles involved in respiration.