In swimming, the process of breathing as part of a very efficient freestyle stroke requires the right timing, the right head alignment with one's spine and body, and the right feeling for water flow dynamics. A good, fast swimmer creates a trough in the water that allows one to turn the head only slightly instead of turning the head far enough for their mouth to totally clear the water. Not having to exaggerate the head lift saves energy and preserves overall alignment. Additionally, one needs to exhale through the nose during the time the swimmer's face is underwater and then inhale through the mouth on the intake part of the breathing.
This timing, positioning, and the inhale/exhale cycle dynamic, provides a relaxation that keeps blood pressure lower and the body less tense than inhaling and exhaling solely through the mouth. Not having to turn one's face too far to breath helps to maintain better body alignment which increases overall efficiency. All of which means you swim faster because of these interrelated efficiencies. It's all good.
In photography it's rare that our chosen mentors address proper breathing as it relates to making good photographs. Sure, just like a marksman with a rifle, we know to exhale slowly while "squeezing" the shutter button if we are to have photos with the least amount of camera shake, but there is much more to "photographic breathing" than just helping to ensure stable technique.
Good breathing practices create a calmer and less emotionally reactive photographer which allows for a clearer understand of what it is, exactly, that moves us to make a certain photograph. When one is shooting on the street a calmer affect telegraphs to a subject that there is less risk or danger in dealing with the photographer in front of them. And, for the photographer, it means having a relaxed disposition that's apt to be more flexible to the constantly changing bits and pieces of life on the street.
It will probably strike some readers as a bit silly when I say that I practice relaxed breathing techniques with 100% attention for a couple of minutes every hour through each day. Sounds new age-y but it works to keep my anxiety in check and my heart rate healthier. My routine is to stand up from my computer, if I'm in the office, grab a seat on the floor, settle down and try to reduce my breathing to seven breaths a minutes for two minutes. I try to empty my mind of any agenda. I don't think about clients, don't strategize my next phone call, don't think about the balance in my check book. I watch the second hand on my watch and try to slow down and deepen both my inhale and my exhale cycles. I've experimented doing this with a smart watch that measures heart rate and can watch my heart rate slow down by 4 or 5 beats per minute with just two minutes of "mindful" breathing.
If I've had a stressful day and I find myself getting tense or worried about things in general I also have an end of day breathing exercise that helps put the brakes on anxiety and worry pretty well. I grab an old, blue Ensolite foam pad from a shelf in the studio, unroll it onto the floor and then lie down on my back. I set a watch or phone or computer alarm clock to 20 minutes and then I close my eyes and concentrate on creating a nice, smooth rhythm of breathing in and out while working on relaxing all the muscles in my body. I start with my feet and work my way up to my head, relaxing each part of my body in turn. With practice, over time, this can short circuit a rising worry or spiking anxiety and it leaves me feeling more relaxed and more in control.
When I make portraits, especially on locations where there are so many uncontrollable factors involved I constantly remind myself to keep working on my breathing and that helps me change gears more smoothly when something about a location doesn't work.
If I have to deal with difficult people a sub-routine of good breathing technique goes a long way to cancelling my need to win every argument and helps me slow down and create some sort of emotional space for a better style of collaboration. Rapid breathing makes each of us much more reactive and readies the whole system for action --- even if actual action is not called for. Over-revving our engines does nothing for our performance, it just makes a lot of "noise" and wastes energy. It also puts us into an "action mindset" which compacts our ability to be open to chance.
While it may seem silly, the next time you are getting ready to start a photo session try spending five minutes ignoring everything around you and just settling down and watching your breathing. You might be amazed at how clear your intentions and actions become with a little practice. Concentrating on good breathing is also good for your posture as the best breathing requires good body position to maximize the oxygen intake. And better posture has its own rewards.
Side note: I've recently been working on breathing practice as a preventative to overbuying expensive cameras. If I find a super cool camera at a (breathtaking!!!) incredibly low price and feel like I should jump on it immediately I have a new "desire disruptor" drill that involves walking away from my desk, sitting in a comfortable chair and breathing with my full attention for five minutes. Usually, afterwards, I close the alluring camera website, log out, and I've dodged another unneeded, multi-thousand dollar expense. It doesn't always work but with more practice I think I'll get there.
Good breathing is a key to good health and good health means being in better shape physically and mentally which makes taking worthy photographs that much easier.
Breathing. It's not just a substitute for image stabilization!