Effects of Breath-Hold vs Standard Interval Training on Fitness in Mountaineers

July 9, 2026 updated by: Mohammadreza Rezaeipour, MD, PhD

Effects of Mild Voluntary Hypoventilation During Progressive Interval Training on Cardiorespiratory Fitness in Recreational Mountaineers: A Clinical Trial

This study investigated whether adding structured breath-holds to standard interval training improves cardiorespiratory fitness in recreational mountaineers more than interval training alone. Twenty-four male recreational mountaineers participated in an 8-week progressive treadmill interval training program. Participants were divided into two groups: a controlled-breathing group that performed structured mid-tidal breath-holds during training, and a free-breathing group that maintained unrestricted breathing. The primary outcomes measured were resting heart rate and estimated maximal oxygen uptake, along with secondary measures including blood pressure and pulmonary function indices. The study aimed to determine if this mild voluntary hypoventilation technique provides additional physiological benefits for altitude preparation.

Study Overview

Status

Completed

Conditions

Intervention / Treatment

Detailed Description

Recreational mountaineers often train at low altitudes without access to specialized hypoxic facilities. While intermittent hypoxic training is an established preparation strategy, the required equipment is costly and inaccessible. Voluntary hypoventilation training (VHT), which involves deliberate breath-holds during exercise, has been proposed as a low-cost alternative. However, its efficacy at producing mild desaturation levels suitable for recreational settings had not been established.

This retrospective clinical trial evaluated the effects of mild VHT on cardiorespiratory fitness. Twenty-four male recreational mountaineers completed a progressive 8-week treadmill interval training program (24 sessions, 65-85% heart rate reserve) between September and November 2023. Participants were allocated to either a controlled-breathing (CB) group or a free-breathing (FB) group. The CB group performed structured mid-tidal breath-holds synchronized to an electronic metronome during approximately 25% of the main training phase, targeting a peripheral oxygen saturation (SpO₂) nadir of 92-94%. The FB group completed the identical exercise protocol with unrestricted breathing, maintaining SpO₂ at or above 97%.

Physiological assessments were conducted at baseline and within 48 hours post-intervention. Measurements included resting cardiovascular parameters (heart rate and blood pressure), estimated maximal oxygen uptake (VO₂max) via a modified Bruce treadmill protocol, and comprehensive pulmonary function testing (spirometry). Continuous SpO₂ monitoring was utilized during all training sessions to ensure protocol adherence and participant safety.

Study Type

Interventional

Enrollment (Actual)

24

Phase

  • Not Applicable

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Locations

  • Iran
    • Sistan and Baluchestan
      • Zahedan, Sistan and Baluchestan, Iran, 98135-986
        • Sport Sciences Department, University of Sistan and Baluchestan

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Ages Eligible for Study

  • Adult

Accepts Healthy Volunteers

Yes

Description

Inclusion Criteria:

Male recreational mountaineers aged 25 to 35 years. A minimum of 6 months of mountaineering experience with at least 3 sessions per month.

Willingness to attend at least 85% of the scheduled training sessions. Negative responses to all items on the Physical Activity Readiness Questionnaire (PAR-Q).

Exclusion Criteria:

Diagnosed cardiovascular, respiratory, or musculoskeletal disorders. Current smoking. Use of medications affecting heart rate or blood pressure. Prior experience with structured hypoxic or breath-hold training.

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

  • Primary Purpose: Other
  • Allocation: Non-Randomized
  • Interventional Model: Parallel Assignment
  • Masking: Single

Arms and Interventions

Participant Group / Arm
Intervention / Treatment
Experimental: Controlled-Breathing (CB) Group
Participants completed 24 supervised treadmill interval sessions over 8 weeks (65-85% heart rate reserve). During approximately 25% of the main training phase, participants performed structured mid-tidal breath-holds synchronized to an electronic metronome (progressing from 3-count to 6-count cycles), targeting a peripheral oxygen saturation (SpO₂) nadir of 92-94%.
Behavioral: Voluntary Hypoventilation Training
A breathing maneuver consisting of structured mid-tidal breath-holds synchronized to an electronic metronome to induce mild voluntary hypoventilation (target SpO₂ nadir 92-94%) during physical exertion.
Other Names:
  • VHT; Breath-Hold Training
Behavioral: Progressive Treadmill Interval Training
A cardiovascular exercise protocol involving supervised treadmill sessions with progressive increases in intensity (65-85% heart rate reserve) and duration (30-45 minutes) over an 8-week period.
Other Names:
  • Interval Training; Treadmill Exercise
Active Comparator: Free-Breathing (FB) Group
Participants completed the identical 24 supervised treadmill interval sessions over 8 weeks (65-85% heart rate reserve) with unrestricted breathing throughout all sessions. Continuous SpO₂ monitoring confirmed values remained at or above 97%.
Behavioral: Progressive Treadmill Interval Training
A cardiovascular exercise protocol involving supervised treadmill sessions with progressive increases in intensity (65-85% heart rate reserve) and duration (30-45 minutes) over an 8-week period.
Other Names:
  • Interval Training; Treadmill Exercise

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Resting Heart Rate
Time Frame: Baseline (within 48 hours before the first training session) and post-intervention (within 48 hours after the final 8-week training session).
Resting heart rate (beats per minute) recorded using a 12-lead electrocardiograph after 10 minutes of seated rest in a quiet, temperature-controlled room. The mean value from the final 2 minutes is used for analysis.
Baseline (within 48 hours before the first training session) and post-intervention (within 48 hours after the final 8-week training session).
Estimated Maximal Oxygen Uptake (VO2max)
Time Frame: Baseline (within 48 hours before the first training session) and post-intervention (within 48 hours after the final 8-week training session).
Estimated VO2max (mL·kg-¹·min-¹) determined using a modified Bruce treadmill protocol until volitional exhaustion. It is calculated from total treadmill time (in minutes) using the Foster equation.
Baseline (within 48 hours before the first training session) and post-intervention (within 48 hours after the final 8-week training session).

Secondary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Systolic Blood Pressure
Time Frame: Baseline and post-intervention (within 48 hours after the final 8-week training session).
Systolic blood pressure (mmHg) measured in triplicate using an automated oscillometric monitor; the average of 3 measurements is retained.
Baseline and post-intervention (within 48 hours after the final 8-week training session).
Diastolic Blood Pressure
Time Frame: Baseline and post-intervention (within 48 hours after the final 8-week training session).
Diastolic blood pressure (mmHg) measured in triplicate using an automated oscillometric monitor; the average of 3 measurements is retained.
Baseline and post-intervention (within 48 hours after the final 8-week training session).
Tidal Volume (TV)
Time Frame: Baseline and post-intervention (within 48 hours after the final 8-week training session).
Tidal volume (L) measured via calibrated spirometry; the highest value from three technically acceptable maneuvers is retained.
Baseline and post-intervention (within 48 hours after the final 8-week training session).
Vital Capacity (VC)
Time Frame: Baseline and post-intervention (within 48 hours after the final 8-week training session).
Vital capacity (L) measured via calibrated spirometry; the highest value from three technically acceptable maneuvers is retained.
Baseline and post-intervention (within 48 hours after the final 8-week training session).
Forced Vital Capacity (FVC)
Time Frame: Baseline and post-intervention (within 48 hours after the final 8-week training session).
Vital capacity (L) measured via calibrated spirometry; the highest value from three technically acceptable maneuvers is retained.
Baseline and post-intervention (within 48 hours after the final 8-week training session).
Forced Expiratory Volume in 1 Second (FEV1)
Time Frame: Baseline and post-intervention (within 48 hours after the final 8-week training session).
Forced expiratory volume in 1 second (L) measured via calibrated spirometry; the highest value from three technically acceptable maneuvers is retained.
Baseline and post-intervention (within 48 hours after the final 8-week training session).
Peak Expiratory Flow (PEF)
Time Frame: Baseline and post-intervention (within 48 hours after the final 8-week training session).
Peak expiratory flow (L/s) measured via calibrated spirometry; the highest value from three technically acceptable maneuvers is retained.
Baseline and post-intervention (within 48 hours after the final 8-week training session).
Forced Expiratory Flow at 25-75% of FVC (FEF25-75%)
Time Frame: Baseline and post-intervention (within 48 hours after the final 8-week training session).
Forced expiratory flow at 25-75% of FVC (L/s) measured via calibrated spirometry; the highest value from three technically acceptable maneuvers is retained.
Baseline and post-intervention (within 48 hours after the final 8-week training session).
Maximum Voluntary Ventilation (MVV)
Time Frame: Baseline and post-intervention (within 48 hours after the final 8-week training session).
Maximum voluntary ventilation (L/min) measured via calibrated spirometry; the highest value from three technically acceptable maneuvers is retained.
Baseline and post-intervention (within 48 hours after the final 8-week training session).

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

Mohammadreza Rezaeipour, MD, PhD

Collaborators

Mountaineering and Sport Climbing Federation of Sistan and Baluchestan Province
General Directorate of Sports and Youth of Sistan and Baluchestan Province

Investigators

  • Principal Investigator: Mohammadreza Rezaeipour, MD, PhD, University of Sistan and Baluchestan

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Actual)

September 30, 2023

Primary Completion (Actual)

November 30, 2023

Study Completion (Actual)

November 30, 2023

Study Registration Dates

First Submitted

July 9, 2026

First Submitted That Met QC Criteria

July 9, 2026

First Posted (Actual)

July 14, 2026

Study Record Updates

Last Update Posted (Actual)

July 14, 2026

Last Update Submitted That Met QC Criteria

July 9, 2026

Last Verified

July 1, 2026

More Information

Terms related to this study

Keywords

Other Study ID Numbers

  • IR.USB.REC.1402.013

Plan for Individual participant data (IPD)

Plan to Share Individual Participant Data (IPD)?

YES

IPD Plan Description

The de-identified dataset and full study protocol are available from the corresponding author upon reasonable request.

IPD Sharing Time Frame

Without end date

IPD Sharing Access Criteria

Available from the corresponding author upon reasonable request.

IPD Sharing Supporting Information Type

  • STUDY_PROTOCOL

Drug and device information, study documents

Studies a U.S. FDA-regulated drug product

No

Studies a U.S. FDA-regulated device product

No

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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