Carbon Dioxide Inhalation - Risks for Health or Opportunity for Physical Fitness Development?

Sep 30, 2026

Carbon dioxide (CO2) is widely viewed as a metabolic by-product, yet evidence shows it actively regulates multiple physiological systems. Acute hypercapnia triggers respiratory, cardiovascular, metabolic, immune, and neurocognitive responses that can temporarily affect exercise performance. This narrative review synthesizes findings on CO2 inhalation in healthy individuals and evaluates whether controlled hypercapnia could function as a targeted stimulus in sport and exercise, applying criteria that exclude exclusively clinical populations.

LanguageEnglish

CategoryHealthcare

FormatPDF

Pages21

Reading Time53 min

AccessFree to download

Abstract

1. Introduction

Hypercapnia definition and mechanisms

CO2 production, transport, and systemic effects

Review Carbon Dioxide Inhalation—Risks for Health or Opportunity for Physical Fitness Development? Natalia Danek Academic Editor: Stefano Nava Received: 30 November 2025 Revised: 29 December 2025 Accepted: 31 December 2025 Published: 3 January 2026 Copyright: © 2026 by the author. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license. Department of Physiology and Biomechanics, Faculty of Physical Education and Sport, Wroclaw University of Health and Sport Sciences, 51-612 Wroclaw, Poland; [natalia.danek@awf.wroc.pl](natalia.danek@awf.wroc.pl); Tel.: +48-713473358 Abstract Background: Carbon dioxide (CO 2) is traditionally regarded as a metabolic by-product; however, growing evidence indicates that it plays an active regulatory role across multiple physiological systems. Acute hypercapnia elicits respiratory, cardiovascular, metabolic, immune, and neurocognitive responses, some of which may transiently influence exercise performance. This narrative review summarizes current evidence on CO2 inhalation in healthy individuals and critically evaluates whether controlled hypercapnia may serve as a targeted stimulus in sport and exercise contexts. Methods: A narrative review of peer-reviewed English-language articles indexed in PubMed and Web of Science was conducted. A narrative approach was chosen due to the marked heterogeneity of study designs, hypercapnia-induction methods (e.g., CO2 inhalation, voluntary hypoventilation, increased respiratory dead space), participant characteristics, and outcome measures, which precluded systematic synthesis. The review focused on studies involving healthy or physically active individuals and examined acute or short-term hypercapnic exposure. No strict publication date limits were applied. Studies conducted exclusively in clinical populations were excluded. Results: Short-term, controlled hypercapnia reliably increases ventilation, sympathetic activation, cerebral and muscular blood flow, and metabolic stress. Certain hypercapnia-based interventions—such as voluntary hypoventilation or added respiratory dead space—may enhance buffering capacity, reduce lactate accumulation and improve maximal oxygen uptake (VO 2max) during submaximal efforts and repeated-sprint performance during high-intensity, short-duration exercise. However, CO2 inhalation frequently induces dyspnea, anxiety, and cognitive disruption, and higher concentrations pose clear safety risks. Current evidence does not support long-term improvements in VO2max or long-duration endurance performance following hypercapnia-based interventions. Conclusions: Controlled, intermittent hypercapnia may provide a targeted metabolic and ventilatory stimulus that enhances tolerance to high-intensity exercise, yet its application remains experimental and context-dependent. The risks associated with CO2 inhalation in healthy individuals currently outweigh its potential benefits, and safe, effective training protocols have not been fully established. Further research is needed to clarify the mechanisms, long-term adaptations, and practical utility of hypercapnia-based training strategies. Keywords: hypercapnia; CO 2 inhalation; respiratory dead space; voluntary hypoventilation; exercise performance; buffering capacity; sports physiology 1. Introduction Inhalation of carbon dioxide (CO 2)-enriched air increases its partial pressure in arterial blood above 45 mmHg, leading to hypercapnia. Hypercapnia is defined as a condition in which the arterialized blood partial pressure of carbon dioxide (pCO 2) exceeds 45 mmHg [1] . When the elevation in CO2 partial pressure is accompanied by increased carbonic acid (H 2CO3 − ) concentration and a reduction in pH (reflecting elevated hydrogen ion concentration) [2], a state of respiratory (hypercapnic) acidosis develops. Carbonic acid forms asa result of the reaction bet

FAQs

How does CO2 inhalation lead to hypercapnia and what physiological changes follow?

Inhalation of CO2-enriched air increases arterial CO2 partial pressure above 45 mmHg, producing hypercapnia and respiratory acidosis. This activates central and peripheral chemoreceptors, leading to reflex hyperventilation and shifts in acid–base balance.

What potential benefits does controlled short-term hypercapnia offer for exercise?

Short-term, controlled hypercapnia increases ventilation, sympathetic activation, cerebral and muscular blood flow, and metabolic stress. Some hypercapnia-based interventions may improve buffering capacity, reduce lactate accumulation, and enhance VO2max during submaximal or repeated-sprint high-intensity efforts.

What risks and limitations prevent hypercapnia-based interventions from being fully adopted?

CO2 inhalation often causes dyspnea, anxiety, and cognitive disruption, and higher concentrations carry clear safety risks. Current evidence does not support long-term improvements in VO2max or endurance, and safe, effective training protocols remain experimentally unresolved.

Sep 30, 2026

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