[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Physiology](https://durgical.com/en/physiology/) › [Respiratory](https://durgical.com/en/physiology/#s-resp) › The work of breathing

[Physiology](https://durgical.com/en/physiology/) · [Respiratory](https://durgical.com/en/physiology/#s-resp)

# The work of breathing

- Concept
- Exam priority: medium

Breathing costs energy: the lung must be stretched and airway resistance overcome. In asthma or obesity it costs far more.

Updated 2026-11-01

Also called: Cost of breathing

**See it in 3D:** [Diaphragm](https://durgical.com/en/anatomy/diaphragm/) · [External intercostals](https://durgical.com/en/anatomy/external-intercostal-muscles/) · [Internal intercostals](https://durgical.com/en/anatomy/internal-intercostal-muscles/)

## Key points

- Two components: elastic (set by compliance) and resistive (set by airway resistance).
- At rest breathing uses ≈2–5 % of total body O₂ consumption; in severe disease it can take a large share.
- Restrictive pattern (stiff lung): rapid, shallow breaths minimize elastic work.
- Obstructive pattern: slow, deep breaths minimize resistive work; expiration becomes active.
- Dynamic hyperinflation and intrinsic PEEP in COPD and asthma: the flattened diaphragm works at a disadvantage.
- Signs of increased work: accessory muscle use, retractions, nasal flaring, paradoxical breathing.

## What it is

The work of breathing is the energy the inspiratory muscles spend moving air. It has an elastic part (stretching lung and chest wall) and a resistive part (overcoming airway and tissue resistance). At rest expiration is passive and breathing uses a small share of the body's oxygen; in disease that cost can become the cause of muscle fatigue and respiratory failure.

## How it works, step by step

- To inhale, the muscles generate pressure that must overcome elastic recoil and resistance to flow.
- If compliance falls (fibrosis, edema, obesity), each milliliter of volume needs more pressure: elastic work rises.
- If resistance rises (bronchospasm, mucus), each liter per second of flow needs more pressure: resistive work rises.
- In obstruction, expiration does not finish; air is trapped and the next breath starts from a fuller lung.
- The flattened, shortened diaphragm generates less force; muscle O₂ use rises and fatigue sets in.
- When load exceeds muscle capacity, ventilation falls and PaCO₂ rises: hypercapnic failure.

### Lung volumes and capacities

**TLC** 6.7 L **VC** 4.1 L **FRC** 3.5 L **RV** 2.6 L **FEV1/FVC** 0.45

Obstructive (COPD, asthma): air is trapped: ↑ RV and ↑ FRC, TLC normal or ↑, VC ↓. FEV1 falls more than FVC: FEV1/FVC
- IRV · Inspiratory reserve volume
- TV · Tidal volume
- ERV · Expiratory reserve volume
- RV · Residual volume
- Capacity (sum of volumes)
- Current forced expiration
- Normal

Compare the obstructive pattern with normal: the high residual volume is trapped air that forces extra work.

## How the body minimizes the work

| Situation | Dominant component | Pattern adopted |
| --- | --- | --- |
| [Restrictive disease](https://durgical.com/en/conditions/interstitial-lung-disease/) | Elastic | Rapid and shallow |
| [Asthma or COPD](https://durgical.com/en/conditions/asthma/) | Resistive | Slow and deep, prolonged expiration |
| [Obesity](https://durgical.com/en/conditions/obesity/) | Elastic (chest wall) | Rapid, small volumes, worse lying flat |

## Clinical notes

- Asthma attack: a child who stops wheezing and looks tired may be tiring out, not improving.
- Weaning from mechanical ventilation: a high rate-to-tidal-volume ratio (rapid shallow breathing) predicts failure.
- Nursing: count the respiratory rate for a full minute and look for sternocleidomastoid use and retractions.

## Memory aid

Stiff lung, short steps; narrow tube, slow breaths.

## Test yourself

Think of the answer, then tap the question to see it.

## Why does a patient with pulmonary fibrosis breathe rapidly and shallowly?

With a stiff lung, each deep breath needs a lot of elastic pressure; spreading ventilation over many small breaths lowers total work.

## How does dynamic hyperinflation increase the work of breathing in COPD?

Trapped air leaves a positive end-expiratory pressure that must be overcome before air flows in, and it flattens the diaphragm, which loses force.

## Why does expiration, passive at rest, become active in an asthma attack?

Elastic recoil can no longer empty the lung through narrowed airways; abdominal and internal intercostal muscles push, which adds work and compresses the airways.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/physiology/the-work-of-breathing/)

## See it in 3D

The structures of Durgical's 3D anatomy where it happens.

- [Diaphragm](https://durgical.com/en/anatomy/diaphragm/)
- [External intercostals](https://durgical.com/en/anatomy/external-intercostal-muscles/)
- [Internal intercostals](https://durgical.com/en/anatomy/internal-intercostal-muscles/)

## Related topics

- [Mechanics of breathing: pressures and muscles](https://durgical.com/en/physiology/mechanics-of-breathing-pressures-and-muscles/)
- [Lung and chest wall compliance](https://durgical.com/en/physiology/lung-and-chest-wall-compliance/)
- [Airway resistance](https://durgical.com/en/physiology/airway-resistance/)
- [Obstructive and restrictive patterns, and flow–volume loops](https://durgical.com/en/physiology/obstructive-and-restrictive-patterns-and-flow-volume-loops/)
- [Hypoxemic and hypercapnic respiratory failure](https://durgical.com/en/physiology/hypoxemic-and-hypercapnic-respiratory-failure/)

## Related conditions

- [Asthma](https://durgical.com/en/conditions/asthma/)
- [Chronic obstructive pulmonary disease (COPD)](https://durgical.com/en/conditions/chronic-obstructive-pulmonary-disease/)
- [Obesity](https://durgical.com/en/conditions/obesity/)
- [Interstitial lung disease](https://durgical.com/en/conditions/interstitial-lung-disease/)

[← All of physiology](https://durgical.com/en/physiology/)

Educational physiology content; not a diagnostic or treatment guide and no substitute for a health professional's advice. Values are approximate references. No doses are given.

Sources: [22.3 The Process of Breathing](https://openstax.org/books/anatomy-and-physiology-2e/pages/22-3-the-process-of-breathing) (OpenStax (Rice University), 2022); [Asthma](https://www.ncbi.nlm.nih.gov/books/NBK430901/) (StatPearls (NCBI Bookshelf), 2026); [Chronic Obstructive Pulmonary Disease (COPD)](https://www.ncbi.nlm.nih.gov/books/NBK559281/) (StatPearls (NCBI Bookshelf), 2026); Hall JE. Guyton and Hall Textbook of Medical Physiology, 13th ed. (ch. 38). Reference book used to check facts; its text and figures are not reproduced (Elsevier, 2016).

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Representative model, for educational purposes only.

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/physiology/the-work-of-breathing/