As part of the stress "fight or flight" response, our breathing rate temporarily increases, lowering CO2 levels in the body, adapting our bodies to meet the temporary threat. Lowering the CO2 levels in the body causes an increase in body pH (alkalosis) which changes many of the chemical activities in the body. There is an increase in the amount of calcium entering muscles and nerves. Muscles will contract more quickly, more powerfully and for a greater duration than they would normally. The nerves are also more excitable. Overbreathing, making the body alkalotic, allows your body to react more quickly to danger.

A temporary overbreathing adaptation making the body alkalotic had certain selective advantages; those humans who had the better response escaped and stayed alive! So important was this respiratory response to our survival, that the brain developed a "hot line" from our brain to our respiratory muscles that bypassed all other forms of respiratory control, including the normal need of maintaining stable blood carbon dioxide levels and thus a stable acid base balance in our bodies. There were certain, immediate advantages in being able to temporarily override normal body acid base balance, but doing this on a chronic basis unfortunately comes at a cost to the body.

From a historical perspective, any episode of danger was only going to be short-lived. The "fight or flight" response evolved to cope with temporary real stimuli. In this situation, the biochemical changes were a needed temporary response. The response puts on hold the important body functions of tissue repair, digestion and immune surveillance. The body had time to recover from all the temporary changes after the stressful emergency had passed. Temporary stresses are often invigorating and energizing. A few minutes on a rollercoaster can be fun; a few weeks would not be. This same emergency system, designed for a temporary response to real threats thousands of years ago, reacts in the same way to the chronic perceived stresses of our everyday lives. Modern society does not accept us hitting others, or running away. The effect of these stresses on our breathing patterns and bodies are well known, but poorly recognized. Practising quiet breathing reduces the stress response in our bodies.