Welcome to the first instalment of a four-part series of articles on exercise physiology! In this first issue we will look at the lungs, finding out the what, where, why, how and when!

The lungs are the respiratory centre of the body. They allow us to ingest oxygen which provides the basis for the most fundament biological energy process of all – respiration. Without respiration our entire body tissues would be redundant. Respiration is the process of converting the food we eat into a useable fuel.

The lungs are two large, sponge-like organs contained in the thoracic cavity. They control the inhalation and exhalation of air, working as part of the respiratory system and the excretory system.

Breathing

The diaphragm controls the conscious physical act of breathing. The diaphragmatic muscles contract, increasing the size of the thoracic cavity. The pressure inside the cavity then drops and air rushes into the lungs as it follows its concentration gradient. This is known as negative pressure breathing. The diaphragm’s normal relaxed position is recoiled under the lungs, which decreases the thoracic volume.

Exhalation is the same process in reverse. The diaphragm relaxes back to its normal position. This reduction in thoracic volume contracts the lungs, forcing the air out via the trachea.

Physiology

The lungs have an enormous surface area due to their physiological make-up. The trachea (windpipe) extends downward from the base of the larynx (voice box). Numerous cartilage rings strengthen the walls of the trachea – the cartilage also serves to keep the trachea open, allowing air to flow through on its way to the lungs. At its bottom end, the trachea divides into left and right air tubes called bronchi, which connect to the lungs.

Within the lungs, the bronchi branch into smaller bronchi and even smaller tubes called bronchioles. Bronchioles, which are as thin as a strand of hair, end in tiny air sacs called alveoli, where the exchange of oxygen and carbon dioxide actually takes place. Each lung houses about 300 to 400 million alveoli. Estimates suggest the surface area of the lungs is equivalent to a tennis court!

Gaseous Exchange

Gaseous exchange is the process where useful gases from the air are diffused into the bloodstream, and gases to be excreted are forced back into the lungs. The process occurs in the alveoli – the gases exchange over a tiny (one cell thick) membrane, with Oxygen passing into the bloodstream and waste Carbon Dioxide diffusing into the alveoli ready for excretion via exhalation.

Volumes and Capacities

Lung volumes and capacities are measured in various ways, simply due to the large variety in our breathing at particular times and during unique circumstances. The following list will provide you with a comprehensive guide to lung volumes and capacities.

Tidal Volume
Tidal volume is the volume of inspired and expired air during normal breathing. The important point with tidal volume is that the breathing is as normal possible – the forced inspiration of expiration of air is a different term. An average figure for an adult male is around 500ml per breath.

Inspiratory Reserve Volume
Inspiratory Reserve Volume is the amount of air that can be inspired forcefully after the inspiration of the normal tidal volume. An average figure for an adult male is around 3000ml.

Expiratory Reserve Volume
Expiratory reserve volume is the amount of air that can be forcefully expired after expiration of the normal tidal volume. An average figure for an adult male is around 1100ml.

Residual Volume
Residual volume is the volume of air still remaining in the respiratory passages and lungs after the most forceful expiration. An average figure for an adult male is around 1200ml.

Inspiratory Capacity
Inspiratory capacity is tidal volume plus inspiratory reserve volume (the amount of air a person can inspire after a normal expiration). An average figure for an adult male is around 3500ml.

Functional Residual Capacity
Functional residual capacity is the expiratory reserve volume plus the residual volume (the amount of air remaining in the lungs after a normal expiration). An average figure for an adult male is around 2300ml.

Vital Capacity
Vital capacity is the sum of the inspiratory reserve volume, the tidal volume and the expiratory reserve volume. Essentially this is the complete volume of useable space within the lungs. An average figure for an adult male is around 4600ml.

Total Lung Capacity
Total lung capacity is the sum of the inspiratory and expiratory reserve volumes plus the tidal volume and the residual volume. An average figure for an adult male is around 5800ml.

Lung Rates and Terminology

Given the lungs direct link to breathing as a reflex, added to the importance to the body of correct lung function there are various terms and tests to ensure lung function is as it should be. Testing can highlight any potential problems or help to provide a clear diagnosis in the case of lung disease.

Respiratory Rate
Respiratory Rate is the number of breaths we take per minute. The method most often used to assess this is simply a counting of how many times per minute the chest rises and falls – the breathing reflex is centred entirely in the thoracic cavity and as such this is an accepted site to assess respiratory rate. An average figure for an adult male is 12-20 breaths per minute.

Minute Ventilation
Minute ventilation is the product of respiratory rate and tidal volume. Multiplying the frequency of breathing by the volume of the breaths provides a figure for the total amount of air moved in and out of the respiratory system each minute. An average figure for an adult male is between 6000ml and 10000ml.

Oxygen Consumption
Oxygen consumption is the total volume of oxygen inhaled minus the volume of oxygen exhaled.

Carbon Dioxide Production
Carbon dioxide production is the volume of carbon dioxide exhaled minus the volume of carbon dioxide inhaled.

Peak flow
Peak flow is a measure of how fast you can blow air out of your lungs. In so doing, it measures how wide the airways in your lungs are. For people with asthma, this simple test shows how well their asthma is being controlled. In normal populations, it tells us how well their lungs are functioning and make us aware of any potential problems before they become too serious.

The airways can be narrowed for the following reasons:

Their linings are swollen
There is mucus in the airways
The tubes are constricted by the special muscles surrounding the airways.

All of these may happen when you have asthma.

Can the various lung readings and capacities vary?
Yes. All lung readings and capacities will vary according to age, sex, height and fitness. Generally speaking, the bigger and fitter a person is, the higher their capacities and readings will be.

In addition, readings will vary throughout the day. The morning reading is often lower than that of the evening. That is why you should always take both morning and evening readings and, where possible, you should take these readings at the same time each day.

How Do We Increase Lung Capacity?

The term lung capacity is a tad loose – relative to the size of the individual, lung capacity can only increase a certain amount. What can improve through exercise is lung function. The most significant effect of chronic exercise on the lungs is capilliarisation around the alveoli. Capilliarisation is the formation of tiny new blood vessels in a given tissue type. In the lungs capilliarisation around the alveoli increases the surface area for gaseous exchange, which means the body is more efficient at taking in Oxygen and removing Carbon Dioxide.

As a trained body is able to use more Oxygen, it is more efficient and able to deal with strenuous exercise. The oxygen consumption of the body is called the VO2 max, and a very accurate measure of a person’s cardiovascular fitness.

Endurance training, especially interval training will improve lung function and VO2 max. There are various endurance training programmes available on this website. For a personal programme designed especially for your needs and goals, contact the team at Hoyles Fitness using the email address posted on the site.

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