Most people breathe without thinking as an involuntary action. However, a person will sometimes need to use extra muscles to inhale and exhale, which is accessory muscle breathing.

A person needs to be able to take enough oxygen into the lungs to maintain the health of their vital organs and tissues and stay alive.

People with certain medical conditions and young children with muscles that are not yet fully developed may find it difficult to take in enough air using only their primary breathing muscles.

In this case, they must rely on additional, or accessory, muscles to help them breathe.

This article discusses what accessory muscles are and when and why the body may use them.

A person using their accessory muscles to breathe while swimming underwater.Share on Pinterest
A. Martin UW Photography/Getty Images

Most people can breathe without thinking about it. This is an involuntary action.

However, individuals can also take deliberate breaths. For instance, during breathing practices, such as during yoga or childbirth. This makes breathing more of a voluntary action.

Learn more about lung function here.

Involuntary breathing requires airway resistance muscles, which include:

  • the skeletal muscles of the tongue
  • the hyoglossus, styloglossus and stylohyoid muscles
  • the glottis
  • the larynx
  • the pharynx
  • smooth bronchi muscles

Accessory muscles, such as the sternocleidomastoid and scalene muscles, help stabilize the rib cage. Other muscles include the:

  • abdominal muscles
  • upper trapezius
  • internal intercostals
  • subclavius
  • posterior inferior

The body uses different accessory breathing muscles for breathing in and breathing out.

Inspiration means breathing in or inhalation. The accessory muscles of inspiration lift the third, fourth, and fifth ribs to increase space for air in the lungs.

Accessory muscles of inspiration include:

  • the sternocleidomastoid
  • the upper trapexius
  • the serratus anterior
  • the latissimus dorsi
  • the iliocostalis thoracis
  • the subclavius

Expiration means breathing out or exhalation and is typically a passive process.

Accessory muscles of expiration include the:

  • internal intercostals
  • abdominal muscles
  • transversus
  • thoracis
  • subcostales
  • iliocostalis
  • quadratus lumborum
  • serratus anterior
  • serratus posterior inferior
  • latissimus dorsi

For a person in good health, the accessory muscles are not active during regular breathing.

However, they may use these muscles when taking a deliberately deep breath. For example, they can involve them when swimming underwater or forcefully expelling air to blow out birthday cake candles.

If someone has a condition that makes breathing more difficult, the body may automatically activate the accessory muscles during typical breathing. Different life stages may also influence accessory muscle breathing.

It is common to use the accessory muscle to help compensate for respiratory conditions leading to hypoxemia, a lower than typical level of oxygen in the blood, or hypercapnia, when the blood’s carbon dioxide level rises above typical levels.

A person can also use the muscle for systemic conditions that lead to metabolic acidosis, which is when there is excessive acid in their bodily fluids.

COPD is an umbrella condition that makes it more difficult to breathe. It may force the body to activate accessory muscles for expiration.

A 2019 study reported that the diaphragm and intercostal muscles are at a disadvantage in people with COPD because the lungs over-inflate and air becomes trapped.

This leaves the muscles unable to move enough air into and out of the lungs, leading to the use of accessory muscles.

When examining a person with shortness of breath during end-of-life care, doctors look for abnormalities in their breathing rate.

Research shows that these physical signs include the activation of accessory muscles. In some cases, a person’s typical breathing moments reverse. This means that when they inhale, their chest contracts, and when they exhale, their chest expands.

Additionally, the area between their ribs and neck can sink in when they try to breathe in.

A 2022 review discussed the unique condition of newborns in terms of respiratory muscle function.

The researchers explained that the diaphragm of a newborn is not as strong and more likely to fatigue compared with that of an older child or adult.

When this fatigue sets in, the newborn’s body recruits the accessory muscles to help them keep breathing.

A 2019 study explains that the breathing of young children under general anesthesia can deteriorate more dramatically than in adults. This is because they cannot control their breathing to the same extent.

Young children are also more prone to:

  • losing oxygen from their blood
  • airway obstruction
  • fatigue or collapse of the lung

Additionally, their intercostal muscles are not yet properly developed, so they are not as effective in their role as breathing accessory muscles.

If a person appears to be working harder than usual to breathe, it is important to contact a doctor as soon as possible. The doctor will aim to find and treat any underlying causes.

If a person with COPD is using their accessory muscles to help them breathe, their doctor may recommend a technique called pursed-lip breathing.

This breathing technique may help them breathe out more effectively and eventually reduce the reliance on their accessory muscles.

Accessory muscle breathing means using muscles other than those people typically use for breathing to take in and expel enough air.

The body uses certain muscles, including the diaphragm, for inhalation, whereas exhalation is more of a passive process.

Accessory muscle breathing may result from deliberate breathing practices or strenuous exercise. It may also be due to a health condition.

People should contact a doctor as soon as possible if a person appears to be working harder than usual to breathe.