Originally Posted by
Mike T
If you breathe less, your CO2 will rise in both your blood and your lungs, and there will be less room for O2. Our breathing is driven by our CO2 level, and by our blood's acidity, not directly by O2 usage or O2 lack.
At altitude we become breathless as our blood becomes acidic because of anaerobic metabolism, so due to the low O2, but indirectly.
People who rebreathe air from which the CO2 is being removed, thus using up the O2, become muddled and confused before they become breathless.
If you think you breathe too much during exercise try this. Choose a slope you would normally power walk up, and walk up it. Let your breathing settle into its normal pattern. Once this has happened, keep the same pattern/rate of breathing, but breath much more shallowly - you will soon feel the need to breathe more, and you will feel more comfortable doing so. Then, having let your breathing return to its normal pattern for a bit, keep the same pattern/rate but breathe more deeply - you will almost certainly feel fine doing this, even though the deeper breathing is not needed.
Whilst we can breathe "too much", it is far better than breathing too little, or trying to. In general, unless we have diseased lungs, our breathing just does what it needs to do.