A Simple Definition from Kendal:

“Respiration refers to the exchange of gases between the cells of an organism and the external environment. Respiration consists of ventilation and circulation. Ventilation is the movement of gases into and out of the lungs, while circulation is the transport of these gases to the tissues within the body itself.” “Although movement of gases in the lungs and tissues is by diffusion, their transport to and from the environment and throughout the body requires work by the respiratory and cardiac pumps. The respiratory pump is comprised of the muscles of respiration and the thorax, which is made up of the ribs, scapulae, clavicle, sternum and thoracic spine. This musculoskeletal pump provides the necessary pressure gradients to move gases into and out of the lungs in order to ensure adequate diffusion of oxygen and carbon dioxide within the lung.”



The term External Breathing or ‘ventilation’ refers to the process of gas exchange that occurs during, respiration, during which oxygen enters the lungs from the environment as we inhale, and the waste products (i.e., carbon dioxide and water) exit the lungs into the environment as we exhale. Lungs take up a great deal of room in the ribcage, from the top ribs down to the level of the diaphragm.


The term Internal Breathing or ‘circulation’ refers to the movement of gases and waste products that occur ‘inside’ and throughout the body. They travel through the body via our blood vessels into and out of the cells of our body, much like a factory. Once the oxygen has entered the lungs from the environment, the rest of the physiological process of breathing is referred to as ‘internal breathing’.

After the oxygen is delivered through the body via the blood, the oxygen then defuses into to your cells to be used up by the central energy making-factory inside the cell, called the mitichondria to create energy! Concurrent with the creation of energy (ATP) is the need to expulse waste products created from the chemical process of energy creation. This expulsion of waste products happens on your exhalation.

Inspiration Phase

When you inhale, your diaphragm descends. Your body expands: it lengthens, widens and bulges. The curves of your spine increase as the torso as a whole lengthens. You experience greater fullness, length, and space. You expand outward, away from our core.

  1. The work phase of respiration takes place during the inhalation phase. Air is pulled into the lungs from the outer environment by overcoming lung, chest wall, and airway resistance. Muscular effort is required to enlarge the thoracic cavity, which also lowers intra-thoracic pressure. During the inhalation phase, the diaphragm contracts and descends towards the lumbar spine, flattening the convexity of the dome. The descent of the diaphragm and filling of the lungs increases the length of the thoracic cavity and spine, and the three-dimensional expansion of the ribcage. The chest expands forward and ribcage expands horizontally with the lower ribs widening outward and upward like a handle of a bucket being lifted. These are the floating and false ribs. The collarbones also lift during inhalation, making room for air to enter the top of the lungs.
  2. Any muscle that attaches to the ribcage to some degree influence the mechanics of breathing. The external intercostals, located above the diaphragm between adjacent ribs, contract upon inhalation to elevate the middle and upper ribs, with the goal of creating more space for air to move into the lungs. External intercostals are so named because they attach to the outer surface of ribs. Conversely, the crura assist in the descent of the diaphragm by pulling the roof of the diaphragm down towards the lumbar spine where they attach. The descent of the diaphragm, together with the elevation of the ribs, work to decrease intra-thoracic pressure so that air can move more easily into the lungs during inhalation.
  3. As intra-thoracic pressure in the thoracic cavity decreases as the air enters, pressure is exerted in the abdominal cavity below instead. The diaphragm presses down into the abdomen and viscera below (i.e., liver, stomach) causing the intra-abdominal pressure to increase. The exchange of pressure throughout the length of the torso helps to push blood from the inferior vena cava up inwards the heart, assisting to increase blood circulation, movement of gases, and a properly oxygenated body.
  4. As stated, during inhalation, visceral contents in the abdominal cavity are pressed downward by the movement of the diaphragm and lung inflation, which expands the torso and lengthens the spine. The freedom for this to occur is essential for full breaths to take place. A forward distension of the abdominal wall occurs and can be exaggerated inappropriately during body movement when core support is required. Gentle support of the deep abdominal can be required and controlled eccentric lengthening of the pelvic floor, however, excessive abdominal contraction or bracing of the ribcage during inhalation will restrict the downward movement of the diaphragm, stopping the flow and size of the breath.
  5. When the diaphragm is restricted by abdominal tension, whether through exercise, stress, digestive problems, weakness or illness, the accessory breathing muscles at the shoulders and neck will contract in order to lift the ribcage up and create more space at the top part of lungs for air to flow into, referred to as ‘shallow breathing’. Compensatory tension in these shoulder and neck muscles will ensue.

Expiration Phase

When you exhale, your diaphragm ascends. Your body condenses: it shortens, narrows and hollows. The curves of your spine decrease as the torso as a whole shortens. You experience greater emptiness, and often more weight and stillness. You condense , moving inward towards our core.

  1. Expiration results from the passive and elastic recoil of the lungs upon relaxation of the diaphragm following completion of the inhalation. During the exhalation phase, our diaphragm and organs slide upward along the inner walls of the ribcage, returning the diaphragm to its original domed convex shape.
  2. Movements of the diaphragm and ribcage are essentially opposite. During inhalation, the diaphragm descends and ribcage ascends and widens. During expiration, the diaphragm ascends and ribcages descends and narrows. When the abdominal cavity empties as a result of this upward movement of the diaphragm, the ribcage narrows, and the more-mobile lower side ribs draw downward and inward, via the internal intercostals, which act to narrow and draw the ribs downward. Internal intercostal muscles lie between the ribs of the thorax (‘inter’, between; ‘costal’, rib), attaching to the inside surface of the ribs hence, ‘internal’.
  3. In summary, the narrowing of the ribcage, ascending of the diaphragm, downward pull of gravity, and contraction of the internal intercostals and abdominal muscles all support the exhalation phase.


In my next Blog, I contrast shallow breathing and fully diaphragmatic breathing. Soon after, we will explore your pelvic floor, eventually getting to the breathing-exercises that will change your life! Worth waiting for I promise.

Speak soon,


[i] Florence Peterson Kendall and Elizabeth Kendall McCreary, Muscles: Testing and Function. Lippincott Williams and Wilkins, 1993.