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The Respiratory System

The ability to utilise oxygen is vital for all types of performance. On this page we provide an overview of the system that governs oxygen intake and the four distinct stages of 'respiration'.

Respiratory system key terms

As you read through this page and the other respiratory system pages here at ptdirect some of the terms you encounter may be unfamiliar to you. For this reason some of the major terms are defined for you as follows;




A sensory nerve receptor that is stimulated by chemicals in the blood such as oxygen, carbon dioxide and hydrogen ions.




VO2 refers to the volume (amount) of oxygen that is consumed by the body per minute.  It is a measure of a person’s aerobic (with oxygen) fitness.

VO2 max

VO2 max refers to the maximum capacity of an individuals body to transport and utilise oxygen during exercise.  It is a measure of a person’s aerobic (with oxygen) fitness.


This refers to the chemical processes that occur within a living cell that are necessary for the maintenance of life.  In metabolism substances such as fat and glucose are broken down to create energy for vital processes.


This refers to the lungs


This means towards the outside or furthest point of something


Oxygen, which is needed by the body for aerobic metabolism


Carbon dioxide, which is a waste product of metabolism and is acidic

H+ ions

Hydrogen ions, which are a waste product of metabolism and are acidic


This refers to the constant regulation of the body’s internal environment to maintain a stable living condition


Refers to a condition that results in shortness of breath and discomfort with breathing

Valsalva Manoeuvre

Refers to the act of holding your breath and contracting your core muscles when lifting heavy weights.

What is the respiratory system?

The respiratory system refers to the organs and structures of the body that allow you to breathe.  The two main goals of the respiratory system are to:

  1. Deliver oxygen (O2) to the blood and tissues of the body
  2. Remove carbon dioxide (CO2) produced by the body back into the atmosphere 

personal training respiratory system

What does the respiratory system do?

The respiratory system achieves its two main goals through the action of respiration (breathing).  The act of respiration can be divided into four distinct and vital parts, these are:

1.      Pulmonary ventilation – the action of breathing to move air into and out of the lungs. (‘Pulmonary’ refers to the lungs).

2.      Pulmonary gas exchange – the exchange of O2 and CO2 between the blood and the lungs. This is also known as ‘external respiration’.

3.      Respiratory gas transport – the interaction of the respiratory system with the cardiovascular system to transport O2 and CO2 between the lungs and the tissues of the body.

4.      Peripheral gas exchange – the exchange of O2 and CO2 between the blood and the tissues of the body. This is also known as ‘internal respiration’.

Why is the respiratory system important?

The respiratory system is essential for our survival, quite simply without inhalation of oxygen and exhalation of carbon dioxide we would die.  The respiratory system therefore constantly works to ensure this is achieved.personal training sport

However the need for O2 and CO2 changes depending on what we are doing. Think about how your respiration rate changes when you exercise; as we begin exercising and place more demands on our bodies systems, such as the muscular system, the need for O2 inhalation and CO2 exhalation increases.  Exercise also increases blood acidity (H+ ions) levels, which must also be controlled.

The changes in O2, CO2 and H+ ion levels are constantly regulated in order to maintain blood homeostasis (regulation of the body’s internal environment to maintain a stable living condition).  This is because too much O2, CO2 and H+ ions in the blood can have serious consequences and lead to headaches, confusion, sleepiness and even death in extreme cases.personal training blood homeostatis

This regulation in order to maintain blood homeostasis is achieved through the coordination of the respiratory and cardiovascular systems, as they work to ensure the correct balance of O2, CO2 and H+ ions in the blood. Most of this coordination is accomplished by involuntary regulation (autonomic nervous system) of pulmonary ventilation.

The diaphragm (muscle responsible for inspiration and expiration) is controlled by motor neurons which are regulated by respiratory centres in the brain.  These respiratory centres control the rate and depth of breathing and respond to chemoreceptors in the body, which detect the changing O2, CO2 and H+ ion levels.

When the levels of CO2 and H+ ions increases, as they do with exercise, signals are sent to the inspiratory control centre’s to increase the rate and depth of respiration.  This increase in respiration rate and depth results in:

1.      The amount of O2 inspired increasing

2.      The amount of CO2 expired increasing

3.      The amount of H+ ions being removed increasing

This maintains the correct balance of O2, CO2 and H+ ions within the blood, thus maintaining homeostasis.

The respiratory system and fitness

personal training man runningAs we exercise, the respiratory system constantly works to help maintain blood homeostasis.  However another key reason that respiration rate increases with exercise is due to the bodies need to produce energy for our muscles to contract and our internal systems to work.  In fact the respiratory system even needs this energy so that it can do its own job!

One of the key ingredients needed in order for energy to be metabolised from the foods we eat, is oxygen.  So as we begin to use more muscle and place greater demands on our bodies as we exercise, our respiratory system ups the anti in order to supply sufficient oxygen for energy production.

personal training client contactWhen working with clients it’s important to be aware of their respiration rate by watching and listening to them breathe.  This is because it will give you a good indication of how hard they are working and if they are likely to get the intended benefits from the exercise. 

If their breathing rate and depth doesn’t change much then its an indication that they may need to increase the intensity, conversely if their breathing rate is excessively fast and shallow then it is an indication that they need to reduce the intensity or take a rest as they may be over-doing it.  

Being aware of a clients respiratory rate can also help you detect and prevent them from experiencing the following respiratory abnormalities:


personal training shortness of breathDyspnea is the sensation of shortness of breath which generally occurs during exercise when a person who is in poor physical condition tries to exercise at high intensity.  It is due to a significant elevation of blood CO2 and H+ ion concentration due to a lack of O2 and is sensed as an inability to breathe.

The inability of the body to re-adjust blood CO2 and H+ ions is due to respiratory muscles fatiguing and being unable to bring enough air into the lungs to get the extra O2 on board and get rid of accumulated CO2.  This limits the body’s ability to maintain homeostasis.

Dyspnea is a relatively unpleasant sensation and care should be taken when initially prescribing exercise, ensuring that initial exercise intensity corresponds with the physical condition and capabilities of your client.

Valsalva Manoeuvre

personal training weight liftingThe Valsalva Manoeuvre can occur during exercise involving high exertion rates or the lifting of heavy objects.  The manoeuvre occurs when a person holds their breath when performing an exercise.  This causes an increase in 'intra-abdominal pressure' and an increase in 'intra-thoracic pressure' (from contracting muscles of the torso).

As a result air is trapped and pressurised within the lungs in an attempt to stabilise the chest wall.  This causes a restriction in blood return to the heart and lungs which if maintained for a long period decreases cardiac output (blood being pumped out of the heart to the lungs and body).

This manoeuvre should be discouraged in all people particularly people who have high blood pressure or known cardiovascular problems.  Normal breathing, where a person exhales during the concentric exertion of a lift and inhales on the eccentric phase, should be taught and encouraged at all times.

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