Pranayama refers to a yoga breathing practice. It gets really involved if you want to go there.
There is a massive amount of collective belief associated with yoga practices going back five to ten thousand years or more. The people who developed these practices had very well-disciplined minds. This combination adds power to their collective beliefs.
I'm not going to pretend to be qualified to present a detailed explanation of pranayama. Follow that link to a Wikipedia page about it and follow their links and so on if you like.
There are some fine books about yoga practice. Buy some and study them. Patanjali's aphorisms are a great start. You don't need to give up your current beliefs to benefit from studying yoga. The teachings and practices are actually universally applicable.
We hear about people developing pneumonia frequently. What causes it? Shallow breathing using the rib cage is a major culprit.
If you've ever been hospitalized for surgery to the thorax like for an appendectomy, you will likely have been given a gadget for promoting deep breathing to minimize the risk of pneumonia while in recovery.
When inhaling it's best to let your belly expand instead of your rib cage. You take in more air that way and it also squeezes your spleen.
Your spleen contains excess lymphatic fluid. When you breath deeply letting your belly expand it pushes the lymphatic fluid out into your lymphatic system. This is the cleansing effect alluded to when people say "Take a deep cleansing breath." Lymph carries off your cell's waste.
Deep breathing and movement are the ways your lymphatic fluid circulates, it doesn't get pumped around like blood.
That's part of why obese people and sometimes just sort of fat people who don't get up and move and breath correctly have swollen ankles.
Yogis who practice pranayama for many years look like they have a large barrel chest and belly. It's because their lung capacity has increased gradually to the point that they look like beer drinkers.
Ya gotta love it.
Have you noticed that you're pretty calm when you're sleeping? Probably not, because you were asleep.
Except those with sleep apnea, sleeping people breath deeply and slowly letting their bellies expand with each breath.
Deep slow breathing while letting your belly expand is calming. It sends the message to your brain that things are okay.
Shallow rapid breathing using your rib cage is the way people breath during the fight or flight response. This kind of breathing signals the brain that things are not okay. It triggers the release of stress hormones. It makes people anxious and prone to being fearful. Doing it habitually likely will shorten a person's life.
Just be in the habit of breathing deeply and slowly letting your belly expand with each breath, and you'll likely be happier and live longer.
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