Tidal Volume, Vital Capacity and Breathing Rate

This lesson covers the key lung volumes and breathing measurements required by the Edexcel GCSE PE specification (1PE0 — Topic 1). You need to know the definitions of tidal volume, vital capacity, and breathing rate, understand how they change during exercise, and recognise how training affects them.

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Key Definitions

Term	Definition	Typical Value
Tidal volume (TV)	The volume of air breathed in or out in one normal breath at rest	~500 ml
Vital capacity (VC)	The maximum volume of air that can be forcefully exhaled after the deepest possible inhalation	~4,800 ml (males); ~3,200 ml (females)
Breathing rate (BR)	The number of breaths taken per minute	12-20 breaths/min at rest
Minute ventilation (VE)	The total volume of air breathed in or out per minute	VE = TV × BR
Residual volume	The volume of air that always remains in the lungs after maximum exhalation (the lungs never fully empty)	~1,200 ml
Inspiratory reserve volume	The extra volume of air that can be forcefully inhaled beyond a normal tidal breath	~3,100 ml
Expiratory reserve volume	The extra volume of air that can be forcefully exhaled beyond a normal tidal breath	~1,200 ml

Exam Tip: The most commonly tested measurements on Edexcel papers are tidal volume, vital capacity, and breathing rate. You must also know the formula for minute ventilation (VE = TV × BR) and be able to use it in calculations.

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Tidal Volume

Tidal volume is the volume of air breathed in (or out) during one normal, relaxed breath. At rest, this is approximately 500 ml.

How Tidal Volume Changes During Exercise

During exercise, tidal volume increases significantly because the body needs more oxygen:

State	Approximate Tidal Volume
At rest	~500 ml
Light exercise	~1,000-1,500 ml
Moderate exercise	~2,000-2,500 ml
Heavy exercise	~3,000+ ml

The increase in tidal volume is achieved by the stronger contraction of the diaphragm and intercostal muscles, and the recruitment of additional breathing muscles. This draws more air into the lungs with each breath.

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Vital Capacity

Vital capacity is the maximum volume of air that can be forcefully exhaled after the deepest possible inhalation. It represents the total usable lung capacity.

Vital capacity = Tidal volume + Inspiratory reserve volume + Expiratory reserve volume

Factors Affecting Vital Capacity

Factor	Effect
Age	Vital capacity generally decreases with age as lung tissue loses elasticity
Sex	Males typically have a larger vital capacity than females (larger lungs)
Height/body size	Taller individuals tend to have larger vital capacity
Fitness level	Regular aerobic training can increase vital capacity slightly
Smoking	Reduces vital capacity by damaging lung tissue and reducing elasticity

Long-Term Training Effects

Regular aerobic training can lead to a modest increase in vital capacity due to:

• Strengthened respiratory muscles (diaphragm and intercostals).
• Improved elasticity of the lungs and chest wall.
• Increased efficiency of the respiratory muscles.

However, the increase is relatively small compared to other adaptations (such as the improvement in cardiac output).

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Breathing Rate

Breathing rate is the number of breaths taken per minute. At rest, this is typically 12-20 breaths per minute.

How Breathing Rate Changes During Exercise

State	Approximate Breathing Rate
At rest	12-20 breaths/min
Light exercise	20-30 breaths/min
Moderate exercise	30-40 breaths/min
Heavy/maximal exercise	40-60+ breaths/min

What Controls Breathing Rate?

Breathing rate is controlled by the medulla oblongata in the brain. During exercise:

1. Working muscles produce more carbon dioxide (CO₂).
2. Increased CO₂ in the blood is detected by chemoreceptors (in the aorta and carotid arteries).
3. Chemoreceptors send signals to the medulla oblongata.
4. The medulla oblongata sends nerve impulses to the diaphragm and intercostal muscles, increasing the rate and depth of breathing.
5. This ensures more oxygen is delivered to the lungs and more carbon dioxide is expelled.

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Minute Ventilation

Minute ventilation (VE) is the total volume of air breathed in or out in one minute. It is calculated using the formula:

VE = TV × BR

Worked Example 1: At Rest

TV = 500 ml, BR = 15 breaths/min

VE = 500 × 15 = 7,500 ml/min (7.5 l/min)

Worked Example 2: During Exercise

TV = 2,500 ml, BR = 40 breaths/min

VE = 2,500 × 40 = 100,000 ml/min (100 l/min)

Worked Example 3: Finding Breathing Rate

VE = 90 l/min (90,000 ml/min), TV = 3,000 ml

BR = VE ÷ TV = 90,000 ÷ 3,000 = 30 breaths/min

Exam Tip: Edexcel may ask you to calculate minute ventilation, tidal volume, or breathing rate using the formula VE = TV × BR. Make sure you can rearrange the formula and always show your working. Include units in your answer.

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How Lung Volumes Change During Exercise — A Visual Summary

graph TD
    A["During Exercise"] --> B["Tidal volume<br>INCREASES<br>(deeper breaths)"]
    A --> C["Breathing rate<br>INCREASES<br>(more breaths per min)"]
    A --> D["Minute ventilation<br>INCREASES<br>(VE = TV × BR)"]
    A --> E["Inspiratory reserve<br>volume DECREASES<br>(used up by deeper breaths)"]
    A --> F["Expiratory reserve<br>volume DECREASES<br>(more air forced out)"]
    A --> G["Residual volume<br>STAYS THE SAME<br>(lungs never fully empty)"]

    style A fill:#4a90d9,color:#fff
    style B fill:#e67e22,color:#fff
    style C fill:#e67e22,color:#fff
    style D fill:#e67e22,color:#fff

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Long-Term Effects of Training on Breathing

Measurement	Effect of Regular Aerobic Training
Tidal volume at rest	Stays approximately the same
Tidal volume during exercise	May increase slightly (deeper breaths)
Vital capacity	May increase slightly
Breathing rate at rest	Decreases (fewer breaths needed because each breath is more efficient)
Breathing rate during exercise	May decrease at the same intensity (improved efficiency)
Respiratory muscle strength	Increases (diaphragm and intercostals become stronger)
Minute ventilation at rest	Stays approximately the same (lower BR compensated by slightly larger TV)
Maximum minute ventilation	Increases (greater capacity during maximal exercise)

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Common Exam Mistakes