If you are learning proper breathing techniques, you're not just training your body to not breathe as long but You are training your heart, lungs, blood vessels and muscles to actually becoming more efficient in using the oxygen you do take in. If you are efficiently training them to do so, you shouldn't have adverse health effects. Obviously this isn't a matter of just holding your breath, it requires a lot of mental training as well. Simply holding your breath without the mental training will tell your body there's a problem which will actually increase your anxiety and need for oxygen and increase your heart rate. I would suggest doing a lot of research before simply just trying to hold your breath.

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