Understanding Primary and Secondary Breathing Muscles: Functions, Research Insights, and Training Tips

Breathing is something most people do without thinking, yet it relies on a complex system of muscles working together to move air in and out of the lungs. Understanding which muscles are involved, how they function, and how to train them can improve respiratory health, athletic performance, and overall well-being. This post explores the primary and secondary breathing muscles, what research reveals about their roles, and practical ways to strengthen them.

Diagram showing the diaphragm muscle and accessory breathing muscles

Diagram showing the diaphragm muscle and accessory breathing muscles

Primary Breathing Muscles and Their Functions

The primary muscles of breathing are responsible for the main action of inhalation and exhalation during normal, relaxed breathing. These muscles work continuously and automatically to maintain oxygen supply and carbon dioxide removal.

Diaphragm

The diaphragm is the most important muscle for breathing. It is a dome-shaped sheet of muscle located below the lungs, separating the chest cavity from the abdominal cavity.

• When the diaphragm contracts, it flattens and moves downward.

• This increases the volume of the thoracic cavity, creating negative pressure that draws air into the lungs.

• During exhalation, the diaphragm relaxes and returns to its dome shape, pushing air out.

  
  

The diaphragm handles about 60-80% of the work during quiet breathing.

External Intercostal Muscles

These muscles lie between the ribs and assist the diaphragm by elevating the rib cage during inhalation.

• Their contraction expands the chest cavity further.

• They contribute roughly 20-40% of the inhalation effort during normal breathing.

  
  

Together, the diaphragm and external intercostals form the core of the respiratory pump.

Secondary Breathing Muscles and Their Roles

Secondary or accessory breathing muscles come into play when the body demands more oxygen, such as during exercise, stress, or respiratory illness. They help increase the volume and speed of breathing.

Scalene Muscles

Located in the neck, scalene muscles lift the first two ribs, helping expand the upper chest.

• They activate during deep or labored breathing.

• Research shows their increased activity in conditions like asthma or COPD.

  
  

Sternocleidomastoid

Also in the neck, this muscle lifts the sternum (breastbone) to increase chest volume.

• It works alongside the scalenes during heavy breathing.

• Overuse can cause neck tension and discomfort.

  
  

Pectoralis Minor

Found in the chest, this muscle lifts the ribs when the arms are fixed.

• It assists in forced inhalation.

• Tightness here can restrict breathing efficiency.

  
  

Abdominal Muscles

During forceful exhalation, such as coughing or heavy breathing, abdominal muscles contract to push the diaphragm upward and expel air.

• These include the rectus abdominis, transverse abdominis, and obliques.

• They help control breathing during speech and exercise.

  
  
  
  

What Research Says About Breathing Muscles

Scientific studies highlight the importance of both primary and secondary muscles in respiratory health and performance.

• Diaphragm Strength and Endurance: Research shows that diaphragm weakness can lead to breathing difficulties, especially in chronic lung diseases. Training the diaphragm improves lung function and reduces breathlessness.

• Accessory Muscle Overuse: Studies find that over-reliance on secondary muscles often signals respiratory distress or poor breathing habits. This can cause muscle fatigue and pain.

• Breathing Muscle Training: Evidence supports respiratory muscle training (RMT) to enhance strength and endurance of both primary and secondary muscles. RMT benefits athletes, patients with lung disease, and people with breathing disorders.

  
  

For example, a 2018 study published in Respiratory Medicine found that inspiratory muscle training improved exercise capacity and reduced symptoms in patients with chronic obstructive pulmonary disease (COPD).

How to Train Your Breathing Muscles

Training breathing muscles can improve respiratory efficiency, reduce fatigue, and support overall health. Here are practical ways to target both primary and secondary muscles.

Diaphragm Training

• Diaphragmatic Breathing: Lie down or sit comfortably. Place one hand on your chest and the other on your abdomen. Breathe in slowly through your nose, focusing on expanding your belly rather than your chest. Exhale slowly through pursed lips. Practice 5-10 minutes daily.

• Breath Hold Exercises: After a deep diaphragmatic breath, hold your breath for a few seconds before exhaling. This builds diaphragm endurance.

  
  

Strengthening Accessory Muscles

• Neck and Shoulder Mobility: Gentle stretches for the neck and shoulders reduce tension in scalene and sternocleidomastoid muscles.

• Resistance Breathing Devices: Tools like inspiratory muscle trainers provide resistance during inhalation, forcing accessory muscles to work harder.

• Postural Exercises: Good posture supports efficient breathing. Exercises that strengthen the upper back and chest improve accessory muscle function.

  
  

Abdominal Muscle Engagement

• Controlled Exhalation: Practice forceful but controlled exhalations, such as blowing out candles or hissing sounds, to engage abdominal muscles.

• Core Strengthening: Planks, Pilates, and yoga improve abdominal muscle tone, supporting breathing mechanics.

  
  
  
  

Practical Tips for Better Breathing Muscle Health

• Avoid shallow chest breathing, which overuses accessory muscles and can cause tension.

• Incorporate breathing exercises into daily routines, especially if you have respiratory conditions or high physical demands.

• Maintain good posture to allow full lung expansion.

• Stay hydrated and avoid smoking to keep lung tissues healthy.

• Consult a respiratory therapist or physiotherapist for personalized training programs if you have breathing difficulties.

Summery

Breathing depends on a coordinated system of muscles that move air in and out of the lungs. The primary breathing muscles are the diaphragm and external intercostals, which handle most of the work during relaxed breathing by expanding and contracting the chest cavity. The diaphragm alone contributes the majority of breathing effort and is essential for efficient oxygen exchange and carbon dioxide removal.

Secondary or accessory breathing muscles, including the scalenes, sternocleidomastoid, pectoralis minor, and abdominal muscles, become more active during exercise, stress, or respiratory illness. These muscles help increase breathing depth and speed but can become overworked when breathing mechanics are poor. Research shows that weakness in the diaphragm or over-reliance on accessory muscles is linked to breathlessness, fatigue, and reduced performance, while targeted breathing muscle training improves lung function, exercise capacity, and respiratory efficiency.

Breathing muscle health can be improved through diaphragmatic breathing exercises, inspiratory muscle training, posture and mobility work, and core strengthening. Practicing proper breathing techniques, maintaining good posture, and avoiding shallow chest breathing support long-term respiratory health, athletic performance, and overall well-being.

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Disclaimer:

The information shared in this article is for educational purposes only and is not a substitute for professional medical advice. Always consult with your healthcare team before beginning a new exercise program, using supplements, or making dietary changes, especially if you have existing health conditions.