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@Jordan Shakeshaft Hmmm... yes, but I don't see that that study relates to exercise.
Breathing through your mouth means that you breathe out more air per breath and this lowers your level of carbon dioxide. This causes a pH shift towards that means haemoglobin clings much more tightly to oxygen and you don't get the same oxygen release to your exercising muscle cells... therefore peak performance is reduced. Counter to this is that you use a little mor energy to breathe through your nose, but there are many other benefits and so works out as the better option.
Obviously at peak exercise nose breathing can become quite uncomfortable and less efficient, but with lots of specific breathing training exercises and practising exercising with mouth closed it can be learned.
For someone who has done none of this training yes I agree that it is hard, but with practice benefits are gained. Maximising nose breathing also shortens recovery time.
And.... lower levels of CO2 in your blood cause bronchoconstriction, leading to increased airways resistance and making the work of breathing higher.
There's a lot to this, and generally the benefits or nose breathing are poorly understood.
1 year, 6 months ago on How to Breathe for Every Type of Exercise
You said: The Nose vs. Mouth Debate: While there have been some studies comparing nasal and oral breathing during exercise, most have used small sample sizes with somewhat inconclusive results
Reference  is "Influence of nasal airflow temperature and pressure on alae nasi electrical activity."
I don't think this is the right reference. Could you provide an alternative, or if it is the correct reference, please explain how it links to the above.