Being upright is and was the most natural body position. This was the norm during almost the entire history of humanity. Standing also was the norm in factories, plants, shops and offices up to the beginning of the 20th century.
Most modern people prefer to sit. Moreover, we can easily see in offices, colleges, schools and libraries that over 95% of people slouch while sitting and often when standing. The gait of modern people also shows signs of stress and muscular tension. Tense muscles distort our natural grace and elegance.
These negative tendencies are stronger in sick people. Severely sick people have even more muscular tension. They like to lie down during the day as well as at night. Chronic fatigue is a common complaint. Severely ill patients often lie for days and nights, since even sitting requires their muscular and mental efforts.
Why do we have all these negative effects?
The state of our muscles depends mostly on circulation (blood flow) and their oxygenation and relaxation. Medical evidence shows that all these parameters are usually linked together through our unconscious breathing pattern. Let us consider how.
The first respiratory physiologists were called "cardio-respiratory physiologists" since the link between the cardiovascular and respiratory systems, as they found it, was very intimate. Yale University Professor Yandell Henderson, the author of first physiological textbooks, was one of the most prominent scientists in this area. His article "Carbon dioxide" was published in 1940 in Cyclopedia of Medicine. In the section with the title "Relations of Carbon Dioxide and Oxygen in the Body" he wrote, "Moreover, under clinical conditions low oxygen and low carbon dioxide-anoxemia and acapnia-generally occur together. Each of these abnormal states tends to induce and intensify the other."
What does he mean? He claimed that low level of oxygen in the living body usually happens when cellular CO2 is low. Reduced CO2 values are possible only in conditions of over-breathing when we remove too much CO2 from body cells by breathing too heavy. Hence, the heavier we breathe, the less oxygen our bodies have.
Body oxygen content can be evaluated using the stress-free breath holding time test done after usual exhalation. (Exhale normally, pinch the nose, and count the time, but only until the fist signs of stress. As soon as this stress starts to grow, release the nose. After the correct test you should be able to resume your usual breathing pattern.) A century ago ordinary people had about 40-60 s of oxygen in the body.
Breathing of modern people is about 50-80% bigger than it was about a century ago. We are mild hyperventilators.
Numerous medical publications revealed that sick people with diabetes, asthma, heart disease and many other chronic conditions breathe even more (about 2-3 times heavier than the medical norm) without noticing it, but have reduced body oxygenation stores (usually about 10-20 s of oxygen).
In the severely sick these effects are even more pronounced. Breathing is very heavy (audible and visible), but oxygenation is critically low (less than 10 s of oxygen). The sicker we get, the bigger we breathe (even at rest), and the less oxygen our cells have.
What about relaxation of muscles? In 1953 Dr. Brown in his article "Physiological effects of hyperventilation" analysed almost 300 professional studies and stated, "Studies designed to determine the effects produced by hyperventilation on nerve and muscle have been consistent in their finding on increased irritability" (Brown, 1953). This large study was published in Physiological Reviews (October 1953, Volume 33, Issue 4). Hence, the more we breathe, the tenser our muscles are. This is another CO2-related effect.
By the way, usefulness of deep or big breathing is the greatest myth or superstition of modern times. There is no a single medical study that shower or proved that deep breathing is beneficial for health. Meanwhile, thousands of publications revealed negative effects of over-breathing on body oxygenation, perfusion of all vital organs, and state of nerve cells and the immune system.
People in the past had very light and easy breathing pattern (about 4-6 l/min for ventilation). Their bodies had large oxygen stores (about 40-60 s), muscles were relaxed, and they had good postures even without paying attention to it. It is natural for humans to have straight spine 24/7, when breathing is light.
Modern people breathe heavier (about 7-9 l/min). They have less oxygen in the body (about 25-30 s) and some muscular tension manifested in chronic slouching and desire to sit.
Sick people sit or lie for the most of the day. They breathe even bigger (10-20 l/min), but body oxygenation is reduced (10-20 s) and muscles are tense.
Severely sick people breathe very heavy (over 25 l/min), but body oxygenation is critically low (less than 10 s). Muscular tension is so high that they can spend over 12 hours in bed.
There are many factors that make our breathing heavier: stress, breathing through the mouth, sleeping on one's back, lack of physical activity, overeating, pollution, nutritional deficiencies, and many others.
Restoration of body oxygenation is the goal of the Buteyko medical breathing therapy. Russian MDs who practice this therapy noticed that people naturally improve their posture when they improve their body oxygenation. Breathing becomes lighter, muscular tension disappears.
Many western breathing practitioners teach elements of the Buteyko method and educate people about the role of breathing in our health.