The value of Deep Breathing exercise has been taken way more for granted than most exercise systems because it's not always looked at as true exercise yet it's the most important. Certain methods vary depending on the type of breathing you want to focus on and it can be used in so many ways but it has only one goal in mind and that's to train your body from the inside out. The type of methods range from doing Qi Gong, Yoga, what's called Costal Breathing, Specialized Breathing for Posture and for various sports.
I have practiced Deep Breathing exercise for nearly a decade in full detail and different types of research and experimentation. I don't believe in just one method, I use it to help my posture, calm the nerves in my body, used in Isometric exercise and other forms of training so I don't have a particular favorite but I do know that some aren't as efficient as others and whoever claims their method is the greatest just wants to fill their ego and tear down what doesn't work for them but could work for others. Sure it is important to understand the true nature of breathing and with the right kind of training it does more than mellow you out or feel in a calming state of blissfulness; it can help heal injuries, develop greater brain cells, make you faster and/or stronger, help your flexibility and stamina to the point where you can be envious to many or admired by others of your abilities. I won't go into what methods don't work because quite frankly they aren't cut out to be a method that holds true power and longevity.
The two biggest methods in today's society at least of deep breathing are Belly Breathing & a method by Edwin Checkley called Costal Breathing have a small underground debate on which one is superior for real fitness and lifelong health. In my opinion there's only one place where it's debated and Costal is the main flavor but on a serious note in my opinion which one is better? Well let's look at what each one does when it comes to breathing....
A method where you bring the stomach out on an inhale and pulled inward on exhale. This is meant to help relax the muscles of the body and it's been used a method in many ancient Chinese, Japanese & Indian meditative practices where you control the belly to train the organs, lungs and muscles to be in a more calming state of relaxation but still maintaining forms of postures and movements.
I've only read in one other place where Belly Breathing is considered Blasphemy because the people in their "defense" say it gives you a big gut and doesn't maintain youthfulness and health plus in Edwin's book, it's considered Lazy. I'm sorry but that is total bullshit. Babies naturally breathe this way in order for them to survive, call that lazy?
A method where you breathe through the chest and lengthen the rib cage to open up more of the lungs and supposedly helps maintain a classic physique where you have youthful muscle tone in the core area and you hold the stomach in as much as possible to maintain posture.
This is a great method no doubt but like every form of exercise it has it's flaws. Unlike Belly Breathing where you relax the stomach and push outward and pull inward, Costal creates tension because its very difficult to relax when you're constantly trying to pull up the rib cage. This method is mainly used to maintain that "Greek god" like body where you develop a small waistline while having a more muscular structure. The problem I have with this is not the method itself, but the content and the mere snotty intent of what it's "meant" for. I do believe in having an aspiring body but certain things don't always work out in their favor. Me and certainly others have tried for a period of time doing this method almost exclusively and I have come to one conclusion, it hurts like hell and I don't want to feel tensed up trying to maintain my posture. It works for some but it's not meant for everyone.
There is good tension and there's bad tension. Good tension is when you train using form and flexing the muscles in a particular exercise like in Gymnastics, various forms of movement, weightlifting and even swimming. Bad tension is when you use too much muscular flexion and it can cause inflammation and you could hurt yourself in certain situations where unwanted tension can cause injury or worse. I do believe in the type of tension and relaxation that comes from muscle control and flexing the body in various exercises to help maintain form that's acceptable but yet I don't like where i'm forced to tense my body where it becomes painful and can cause possibly a hernia or a tear in the joints and it's not fun where you try to maintain posture but causing too much tension in the back muscles to cramp up and your stomach has a feeling of getting hit with a crowbar (trust me I've been there and it's a pain in the ass).
I have actually maintained a decent posture because of the bridging exercises I practice and it gives me enough tension to maintain form but also give me that natural spring in my torso and hips that give off that powerful posture look. Deep Breathing all together is an essential element to the way we stay alive. The power in your breath can be a breaker or a maker in your health and fitness success. Do what works for you and although there are pros and cons to every method if you read about certain methods that give off a negative vibe or try to tell you that one way is completely wrong and the one you're learning is the best and it's the only one where you live longer and can have this physique and whatnot, i'd think twice about it. Research and observe the content and practice with your own intent and not what someone tells you to do or sets you up with a huge sales pitch. Anything that can be useful in how you build a foundation for health and it gives you purpose without an agenda or a preaching sales pitch then do it. Be your own teacher.