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Completed

NCT Number: NCT07703839

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

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.

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Key information

Conditions

Healthy Volunteers

Age range

25 year–35 year

Sex eligibility

Male

Study type

Interventional

Phase

Not applicable

Primary location

Sport Sciences Department, University of Sistan and Baluchestan

Zahedan, Sistan and Baluchestan, 98135-986, Iran

About this study

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.

Who can participate

Healthy volunteers accepted: Yes

Only the study team can determine whether someone qualifies for participation.

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.

Treatment and study plan

Voluntary Hypoventilation Training

Behavioral

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

Progressive Treadmill Interval Training

Behavioral

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

Primary outcomes

  1. 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.

  2. 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.

Secondary outcomes

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

Sponsors and collaborators

Lead sponsor

Mohammadreza Rezaeipour, MD, PhD

Other

Collaborators

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

Registry information

Official study title

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

Important dates

Study start
2023
Primary completion
2023
Study completion
2023
First posted
Jul 14, 2026
Registry last updated
Jul 20, 2026

OpenTrials presents study information sourced from ClinicalTrials.gov. The official registry record should be consulted for the latest information.

View the official ClinicalTrials.gov record (opens in a new tab)

This listing is for discovery and informational purposes only. It is not medical advice, does not guarantee that a study is recruiting, and does not determine eligibility. Contact the study team and a qualified healthcare professional when considering participation.

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