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[Physiology](https://durgical.com/en/physiology/) · [Temperature, exercise and metabolism](https://durgical.com/en/physiology/#s-integrative)

# Exercise and training physiology

- Regulation
- Exam priority: high

During exercise the heart pumps more, the lungs move more air and muscle pulls more oxygen; training improves every step.

Updated 2026-11-01

Also called: VO₂ max, Lactate threshold

**See it in 3D:** [Left ventricle](https://durgical.com/en/anatomy/left-ventricle/) · [Right lower lobe](https://durgical.com/en/anatomy/inferior-lobe-of-right-lung/) · [Left lower lobe](https://durgical.com/en/anatomy/inferior-lobe-of-left-lung/)

## Key points

- VO₂ = CO × (CaO₂ − CvO₂) (Fick): it rises through cardiac output (up to 4–6-fold) and a wider arteriovenous O₂ difference.
- A trained athlete has a low resting HR because stroke volume is larger; VO₂ max is limited mainly by the heart.
- Ventilation rises in proportion to CO₂ produced: PaO₂ and PaCO₂ barely change in moderate exercise.
- Above the lactate threshold glycolysis outpaces oxidation; bicarbonate buffers and ventilation rises further (extra CO₂).
- Systolic BP rises and diastolic holds or falls (muscle vasodilation); in isometric exercise both rise.

## What it is

Exercise can raise muscle oxygen demand 15–20-fold. The body answers with more cardiac output, redistribution of flow to muscle, more ventilation and greater O₂ extraction in tissue. Endurance training raises stroke volume and mitochondria; strength training enlarges muscle fibres.

## How it works, step by step

- The motor cortex drives muscle and the cardiovascular centre in parallel (central command); muscle ergoreceptors add to it.
- Sympathetic output raises HR and contractility; the muscle pump boosts venous return and stroke volume.
- Local metabolites (K⁺, adenosine, CO₂, H⁺, NO) dilate muscle arterioles; viscera and inactive skin constrict.
- In muscle capillaries heat, CO₂ and acid shift the hemoglobin curve right: more O₂ is unloaded.
- The first seconds run on ATP and phosphocreatine; then glycolysis and, in long efforts, oxidation of fat and glucose.
- After exercise, extra O₂ use persists (EPOC) to restore phosphocreatine, clear lactate and cool down.

### Oxygen–hemoglobin dissociation curve

**P50** 38.5 mmHg **Arterial blood** 93 % **Mixed venous blood** 53 % **O₂ given up to the tissues** 40 %

Right shift (P50 38.5 mmHg): Hb has less affinity and gives up more O₂ in the tissues. Acid, CO₂, heat and 2,3-BPG cause it.

- Current curve
- Normal curve (pH 7.40 · 37 °C)
- Arterial blood (PO₂ 100)
- Mixed venous blood (PO₂ 40)
- O₂ given up to the tissues

In working muscle, acid, CO₂ and heat release more O₂. Compare with «Normal».

## Equations

**Fick principle**VO2 = CO × (CaO2 − CvO2)

**CO**
cardiac output

**CaO₂ − CvO₂**
arteriovenous O₂ difference

At rest the difference is ≈5 mL O₂/dL; at peak exercise it can triple.

## Approximate values (young adult)

| Parameter | Value | Note |
| --- | --- | --- |
| Cardiac output | ≈5 L/min at rest → 20–25 L/min | elite athletes >30 L/min |
| Muscle blood flow | ≈1 L/min → up to ≈20 L/min | |
| Ventilation | ≈6 L/min → 100–150 L/min | |
| VO₂ | ≈250 mL/min (3.5 mL per kg per minute = 1 MET) | VO₂ max ≈35–45 mL per kg per minute if sedentary |
| Maximum HR | ≈220 − age (rough) | |

Approximate values for a healthy adult at rest; each laboratory sets its own ranges.

## Clinical notes

- Stable angina: exercise raises HR and shortens diastole, when the left ventricle is perfused; the plaque prevents coronary flow from rising.
- Beta-blockers blunt exercise HR: the maximum-HR formula does not apply to these patients.
- Regular exercise raises insulin sensitivity (GLUT4 via AMPK, insulin-independent) and lowers resting BP.
- In Bogotá VO₂ max is lower than at sea level for the first days; acclimatized athletes compensate with more hemoglobin.

## Memory aid

«Bigger pump, wider pipes, more extraction»: cardiac output, muscle vasodilation and the AV difference.

## Test yourself

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

## Why does a marathon runner have a resting HR of 45/min with the same cardiac output as a sedentary person?

Training enlarges the ventricle and its stroke volume; with more volume per beat fewer beats are needed (higher vagal tone).

## What happens to PaCO₂ during moderate aerobic exercise, and why?

It barely changes: ventilation rises in step with CO₂ production. It falls only above the lactate threshold, when breathing increases to compensate for acidosis.

## Why does exercise lower blood glucose in someone with insulin resistance?

Contraction activates AMPK and moves GLUT4 to the membrane by an insulin-independent route, so muscle takes up glucose.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/physiology/exercise-and-training-physiology/)

## See it in 3D

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

- [Left ventricle](https://durgical.com/en/anatomy/left-ventricle/)
- [Right lower lobe](https://durgical.com/en/anatomy/inferior-lobe-of-right-lung/)
- [Left lower lobe](https://durgical.com/en/anatomy/inferior-lobe-of-left-lung/)

## Related topics

- [Fed and fasting states: the hormonal switch](https://durgical.com/en/physiology/fed-and-fasting-states-the-hormonal-switch/)
- [Body temperature regulation](https://durgical.com/en/physiology/body-temperature-regulation/)
- [High altitude and acclimatization](https://durgical.com/en/physiology/high-altitude-and-acclimatization/)
- [Heat exhaustion and heat stroke](https://durgical.com/en/physiology/heat-exhaustion-and-heat-stroke/)

## Related conditions

- [Stable angina](https://durgical.com/en/conditions/stable-angina/)

## In Biochemistry

- [Exercise metabolism](https://durgical.com/en/biochemistry/topics/exercise-metabolism/)
- [Lactate](https://durgical.com/en/biochemistry/molecules/lactate/)
- [Cori cycle](https://durgical.com/en/biochemistry/topics/cori-cycle/)
- [mTOR (mechanistic target of rapamycin)](https://durgical.com/en/biochemistry/enzymes/mtor/)
- [AMP-activated protein kinase (AMPK)](https://durgical.com/en/biochemistry/enzymes/amp-activated-protein-kinase/)

## In Pharmacology

- [Propranolol](https://durgical.com/en/pharmacology/propranolol/)

[← 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: [10.6 Exercise and Muscle Performance](https://openstax.org/books/anatomy-and-physiology-2e/pages/10-6-exercise-and-muscle-performance) (OpenStax (Rice University), 2022); [22.6 Modifications in Respiratory Functions](https://openstax.org/books/anatomy-and-physiology-2e/pages/22-6-modifications-in-respiratory-functions) (OpenStax (Rice University), 2022); [Benefits of Exercise: MedlinePlus](https://medlineplus.gov/benefitsofexercise.html) (MedlinePlus, US National Library of Medicine, 2026); Hall JE. Guyton and Hall Textbook of Medical Physiology, 13th ed. (ch. 85). 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/exercise-and-training-physiology/