Dominic Stone
The diaphragm is the primary muscle of inspiration, responsible for breathing by aiding in the expansion and contraction of the thoracic cavity. During inhalation, the diaphragm contracts, moving caudally (downward) and its edges move cranially (upward), compressing the abdominal cavity and raising the ribs outward, thereby expanding the thoracic cavity and drawing air into the lungs. The intercostal muscles, which are attached between the ribs, also play a role in inspiration, with the external intercostals assisting with normal quiet breathing. Other accessory muscles of inspiration include the sternocleidomastoid, scalenes, serratus, and pectoralis muscles, which contribute more during active breathing periods, such as during exercise or forced breathing maneuvers.
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What You'll Learn
The diaphragm
Paralysis or weakness of the diaphragm can lead to serious health issues. Unilateral diaphragmatic paralysis is usually asymptomatic, but paralysis on both sides can result in poor exercise tolerance, orthopnea, and fatigue. Other conditions such as neuromuscular disorders, multiple sclerosis (MS), ALS, diabetes-related neuropathy, spinal cord injuries, or lung issues like chronic obstructive pulmonary disease (COPD) can also affect diaphragm function, leading to symptoms such as acid reflux, heartburn, cough, and difficulty swallowing. Diaphragmatic breathing exercises can help strengthen the diaphragm and improve its function.
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Intercostal muscles
The intercostal muscles are a group of intrinsic rib cage muscles that occupy the 11 intercostal spaces between the ribs. They are involved in the mechanical aspect of breathing by helping to expand and contract the chest cavity. They are divided into three groups: external, internal, and innermost intercostals.
The external intercostal muscles, also known as intercostalis externus, aid in quiet and forced inhalation. They originate on ribs 1–11 and have their insertion on ribs 2–12. The contraction of these fibres raises each rib toward the rib above, with the overall effect of raising the rib cage, assisting in inhalation. The external intercostals are the most superficial intercostal muscles and are responsible for the elevation of the ribs and bending them more open, thus expanding the transverse dimensions of the thoracic cavity.
The internal intercostal muscles, also known as intercostalis internus, aid in forced expiration (quiet expiration is a passive process). They originate on ribs 2–12 and have their insertions on ribs 1–11. The internal intercostals are responsible for the depression of the ribs and bending them inward, thus decreasing the transverse dimensions of the thoracic cavity.
The innermost intercostal muscles, also known as intercostalis intimus, are the deepest intercostal muscles. They originate from the costal groove of one rib, posteriorly to the origin of the internal intercostals. They assist the internal and external intercostals in their function. All three layers of intercostal muscles support the rib cage and are accessory respiratory muscles that participate in the process of forced breathing.
Intercostal muscle strain can occur due to weakened muscles, overexertion, direct trauma from falling or accidents, or contact sports. Symptoms include pain, inflammation, and difficulty breathing.
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Accessory muscles
The diaphragm is the major muscle responsible for breathing. It is a thin, dome-shaped muscle that separates the abdominal cavity from the thoracic cavity. During inhalation, the diaphragm contracts, so its centre moves caudally (downward) and its edges move cranially (upward). This compresses the abdominal cavity, raises the ribs upward and outward, and thus expands the thoracic cavity. This expansion draws air into the lungs.
The intercostal muscles are another important group of respiratory muscles. These muscles are attached between the ribs and are important in manipulating the width of the rib cage. There are three layers of intercostal muscles. The external intercostal muscles are most important in respiration. The contraction of these fibres raises each rib toward the rib above, with the overall effect of raising the rib cage, assisting in inhalation.
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Breathing exercises
The diaphragm is the most important muscle of inspiration, but the intercostal muscles also assist with normal quiet breathing. During inhalation, the diaphragm contracts, moving caudally (downward) and its edges move cranially (upward). This compresses the abdominal cavity, raises the ribs, and expands the thoracic cavity, allowing air to enter the lungs.
Diaphragmatic Breathing
- Breathe in slowly and deeply through your nose. Your abdomen should rise, but your upper chest should remain still and relaxed.
- Breathe out slowly through pursed lips for twice as long as the inhalation. As you breathe out, slowly and gently pull your abdomen towards your spine.
- Repeat 5 times.
Overhead Chest Stretch
- Sit in a supportive chair or lean back in bed.
- Gently squeeze your shoulder blades back and down.
- Hold your hands together and slowly raise your hands as high over your head as is comfortable while taking a deep breath in.
- Slowly lower your hands while breathing out.
- Relax for one to two seconds, then repeat 5 times.
Deep Breathing 4-8-8
- Breathe in through your nose for 4 seconds.
- Hold your breath for 8 seconds, if you can.
- Breathe out through pursed lips for 8 seconds.
- Relax for one to two seconds, then repeat 3 times.
Shoulder Rolls
- Bring your shoulders forward, up, backward, and down in a circular motion.
- Repeat 5 times, making the circles as big as you can and moving both shoulders simultaneously.
- If you have tightness across your chest, start with smaller circles and gradually increase their size.
Resistance Strength Training
Resistance strength training is a type of breathing exercise that involves breathing against a resistance. Two examples include:
- Breathing through a small opening (flow resistance).
- Breathing around a spring-loaded valve (pressure resistance).
Endurance Training
Endurance training involves breathing at an above-normal respiratory rate and tidal volume for a prolonged period, usually 30 minutes. This type of training is also known as voluntary isocapnic hyperpnea (VIH) and requires specialised equipment and supervision.
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Respiratory distress
The diaphragm is the primary muscle responsible for breathing, and it contracts and relaxes to facilitate inhalation and exhalation, respectively. During inhalation, the diaphragm contracts, moving caudally (downward) and drawing air into the lungs. When the diaphragm relaxes, the lungs recoil, forcing air out. In addition to the diaphragm, the intercostal muscles between the ribs also play a crucial role in respiration by manipulating the width of the rib cage.
The use of accessory muscles during quiet breathing can also indicate respiratory distress. These muscles, including the sternocleidomastoid and the scalenes, assist in elevating the rib cage during increased respiratory effort. The involvement of these muscles suggests that the person is exerting more effort to breathe and may be a sign of respiratory distress.
Respiratory muscle training (RMT) is a method to improve the strength and endurance of inspiratory and expiratory muscles. This training can be particularly beneficial for individuals with lung diseases or regular exercisers who may be more conscious of their breathing. Inspiratory muscle training has gained significant attention in medical literature, and various devices are available to enhance respiratory muscle performance.
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Frequently asked questions
The diaphragm is the most important muscle of inspiration. However, the external intercostals assist with normal quiet breathing. Other muscles of inspiration include the scalenes, serratus, pectoralis, sternocleidomastoids, and levator labii superioris alaeque nasi.
The muscles of inspiration contract to draw air into the lungs. This is known as inhalation or inspiration.
The diaphragm is a thin, dome-shaped muscle that separates the abdominal cavity from the thoracic cavity. During inspiration, the diaphragm contracts, moving its centre downwards and its edges upwards. This compresses the abdominal cavity, raises the ribs, and expands the thoracic cavity, allowing air to enter the lungs.
Inspiration is the phase of ventilation in which air enters the lungs, while expiration is the phase in which air is expelled from the lungs. During inspiration, the thoracic cavity and lungs expand, leading to a decrease in pressure within the lungs. This lower pressure causes air to move into the lungs. During expiration, the inspiratory muscles relax, reducing the volume of the thoracic cavity and lungs, and increasing pressure within the lungs, which forces air out.
Breathing is usually controlled automatically by the respiratory centre at the base of our brain. The brain determines when we need to breathe based on signals received from our organs and nerves. We can also control our breathing consciously, such as during speech or voluntary breath-holding.
