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NCT Number: NCT06575985

Mechanisms Underlying Hypoxic, Heat and Cross-tolerance Adaptation in Women

This study will consist of a parallel-groups design, with 30 healthy active female participants randomly assigned to either an experimental heat acclimation and exercise intervention, or a thermo-neutral exercise intervention control group. Interventions will be 10 days in duration, and consist of daily 60-minute exercise bouts under the appropriate environmental condition. Before and after each intervention, various tests will be conducted to establish exercise capacity under various environmental conditions, as well as underlying mechanisms of physiological adaptation induced by each intervention.

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Key information

Conditions

Heat Exposure Exercise Training

Age range

18 year–35 year

Sex eligibility

Female

Study type

Interventional

Phase

Not applicable

Primary location

Jozef Stefan Institute, Ljubljana, SI, Slovenia

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About this study

Most research on how the human body responds to different environmental conditions has primarily focused on men, leaving a gap in our understanding of how women adapt to these conditions. Heat exposure in particular is known to affect the well-being and performance of humans, as well as induce chronic adaptations through an acclimation/acclimatization process, which helps the body to better regulate core temperature. Moreover, contemporary research is beginning to explore the 'cross-tolerance' phenomenon; the notion that exposure (and acclimation/acclimatization) to one environmental stressor may affect the responses to another. In particular, both heat and hypoxia are known to activate common acclimatization pathways, with pulmonary, cardiovascular, hematological and muscular adaptations occurring to facilitate both oxygen transport and core body temperature regulation. In line with this background, the primary aim of this study is to investigate the effects of a heat acclimation and exercise intervention, relative to a thermo-neutral exercise control intervention, on exercise tolerance under various environmental conditions (heat, hypoxia, neutral) in healthy, active women. The secondary aim is to establish mechanisms of adaptation, by exploring the intervention-induced changes in pulmonary, cardiovascular, hematological and muscular factors, through various tests conducted at rest and during exercise.

To address these aims, 30 healthy active female participants, aged between 18 and 35 years, will be randomized to either an experimental (heat acclimation and exercise training) or control (thermo-neutral exercise training) group. The experimental group will complete a 10-day heat acclimation training intervention, exercising for 60 minutes per day in a climactic chamber set to 35°C and 50% relative humidity. The control group will complete a similar exercise intervention, but under thermo-neutral conditions (23°C and 50% relative humidity). Before and after the intervention period, both groups will complete a wide variety of tests, including exercise capacity measurements under each environmental condition (heat [35°C], hypoxia [Fraction of inspired oxygen = 0.135], neutral [23°C, FiO2 = 0.209]), body composition assessments, lung function testing, hemoglobin mass and blood volume quantification, skeletal muscle mitochondrial function and vascular responsiveness assessment, and venous blood sampling for a variety of sex hormone-, redox balance-, hematopoietic-, heat shock protein-, hypoxia-inducible factor- and genetic-related markers.

Who can participate

Healthy volunteers accepted: Yes

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

Inclusion criteria

  • Age: 18 - 35 years
  • Body mass index: 18.5 - 25.0 kg/m^2
  • Regular physical activity (at least 30 minutes of moderate-intensity activity, three times per week)

Exclusion criteria

  • Habitual smoker within the past 5 years
  • History of metabolic disorders or any medications deemed to pose an undue risk or introduce bias in any outcome measures
  • Exposure to altitude > 2000 m above sea level within four weeks of scheduled participation
  • Permanent residence at altitude > 1000 m above sea level

Treatment and study plan

Heat acclimation and exercise training

Other

10-day intervention consisting of daily 60-min exercise sessions aimed to induce increases in core body temperature, conducted in a climactic chamber set to 35°C and 50% relative humidity.

Thermo-neutral exercise training group

Other

10-day intervention consisting of daily 60-min exercise sessions conducted in a climactic chamber set to 23°C and 50% relative humidity.

Primary outcomes

  1. Exercise capacity under thermo-neutral normoxic conditions

    Time frame: Measured once before (pre) and once up to 1 week after (post) the intervention period

    Results of an incremental exercise test to exhaustion conducted at 23°C and an FiO2 of 0.209, quantified using maximal oxygen uptake

  2. Exercise capacity under hot normoxic conditions

    Time frame: Measured once before (pre) and once up to 1 week after (post) the intervention period

    Results of an incremental exercise test to exhaustion conducted at 35°C and an FiO2 of 0.209, quantified using maximal oxygen uptake

  3. Exercise capacity under thermo-neutral hypoxic conditions

    Time frame: Measured once before (pre) and once up to 1 week after (post) the intervention period

    Results of an incremental exercise test to exhaustion conducted at 23°C and an FiO2 of 0.135, quantified using maximal oxygen uptake

Secondary outcomes

  1. Core body temperature regulation during exercise

    Time frame: Measured once before (pre) and once up to 1 week after (post) the intervention period

    Core body temperature measured throughout the incremental exercise tests using a rectal temperature probe.

  2. Skin temperature regulation during exercise

    Time frame: Measured once before (pre) and once up to 1 week after (post) the intervention period

    Skin temperature measured throughout the incremental exercise tests using temperature probes attached to the calf, thigh, chest and arm, from which weighted averages are calculated.

  3. Sweat rates during exercise

    Time frame: Measured once before (pre) and once up to 1 week after (post) the intervention period

    Sweat rate measured throughout the incremental exercise tests using a sensor attached to the forehead.

  4. Hemo-dynamic activity during exercise

    Time frame: Measured once before (pre) and once up to 1 week after (post) the intervention period

    Cardiac output measured throughout the incremental exercise tests by bio-electrical impedance cardiography.

  5. Pulmonary ventilation during exercise

    Time frame: Measured once before (pre) and once up to 1 week after (post) the intervention period

    Pulmonary ventilation measured throughout the incremental exercise tests using flow measurements as recorded by metabolic cart.

  6. Gas exchange during exercise

    Time frame: Measured once before (pre) and once up to 1 week after (post) the intervention period

    Balance of oxygen uptake and carbon dioxide production measured throughout the incremental exercise tests using gas composition sensors recorded by metabolic cart.

  7. Muscle oxygenation during exercise

    Time frame: Measured once before (pre) and once up to 1 week after (post) the intervention period

    Vastus lateralis oxygenation measured throughout the incremental exercise tests using near-infrared spectroscopy.

  8. Brain oxygenation during exercise

    Time frame: Measured once before (pre) and once up to 1 week after (post) the intervention period

    Cerebral oxygenation measured at the left pre-frontal cortex throughout the incremental exercise tests using near-infrared spectroscopy.

  9. Pulse oxygen saturation during exercise

    Time frame: Measured once before (pre) and once up to 1 week after (post) the intervention period

    Capillary oxygen saturation measured on the right earlobe throughout the incremental exercise tests using pulse oximetry.

  10. Body composition

    Time frame: Measured once before (pre) and once up to 1 week after (post) the intervention period

    Body mass measured using standard weighing scales, with body fat percentage estimated using a standardized eight-site skinfold measurement protocol with associated equation.

  11. Lung function

    Time frame: Measured once before (pre) and once up to 1 week after (post) the intervention period

    Standard spirometry procedure to assess lung function using forced expiratory volume

  12. Hemoglobin mass

    Time frame: Measured once before (pre) and once up to 1 week after (post) the intervention period

    Hemoglobin mass estimation using the carbon monoxide re-breathing method

  13. Blood/plasma volume

    Time frame: Measured once before (pre) and once up to 1 week after (post) the intervention period

    Blood/plasma volume estimation using the carbon monoxide re-breathing method

  14. Skeletal muscle mitochondrial function

    Time frame: Measured once before (pre) and once up to 1 week after (post) the intervention period

    Skeletal muscle mitochondrial function quantified using a peripheral vascular occlusion test, with the rate of decrease in muscle oxygenation used to estimate mitochondrial function.

  15. Skeletal muscle vascular responsiveness

    Time frame: Measured once before (pre) and once up to 1 week after (post) the intervention period

    Skeletal muscle vascular responsiveness quantified using a peripheral vascular occlusion test, with the rate of increase in muscle oxygenation during re-perfusion, and the oxygenation overshoot relative to pre-occlusion baseline, used to estimate vascular responsiveness.

  16. Blood viscosity

    Time frame: Measured once before (pre) and once up to 1 week after (post) the intervention period

    Blood viscosity will be measured by obtaining venous blood samples from the participants, extracting plasma, and using a cone/plate viscometer to quantify viscosity and varying shear rates.

  17. Oxidative stress marker

    Time frame: Measured once before (pre) and once up to 1 week after (post) the intervention period

    Venous blood samples will be obtained to quantify redox balance from the extracted plasma.

  18. Hematopoiesis

    Time frame: Measured once before (pre) and once up to 1 week after (post) the intervention period

    Venous blood samples will be obtained to measure various markers of hematopoiesis from the extracted plasma, serum and/or whole blood.

  19. Heat shock proteins

    Time frame: Measured once before (pre) and once up to 1 week after (post) the intervention period

    Venous blood samples will be obtained to measure heat shock proteins in the extracted plasma and serum.

  20. Hypoxia-inducible factor 1α

    Time frame: Measured once before (pre) and once up to 1 week after (post) the intervention period

    Venous blood samples will be obtained to measure hypoxia-inducible factor 1α in the extracted plasma and serum.

Other outcomes

  1. Oestrogen

    Time frame: Measured once before (pre) and once up to 1 week after (post) the intervention period

    Oestrogen will be quantified in the plasma extracted from venous blood samples, to identify the menstrual cycle phases of the participants.

  2. Progesterone

    Time frame: Measured once before (pre) and once up to 1 week after (post) the intervention period

    Progesterone will be quantified in the plasma extracted from venous blood samples, to identify the menstrual cycle phases of the participants.

  3. Single nucleotide polymorphisms

    Time frame: Measured once before (pre) and once up to 1 week after (post) the intervention period

    Venous blood samples will be processed and analysed to identify single nucleotide polymorphisms

Study contacts

Contact information is provided by the study sponsor or research team.

Benjamin J Narang, MSci

CONTACT

[email protected]

+38640569967

Tadej Debevec, PhD

CONTACT

[email protected]

+38615207726

Sponsors and collaborators

Lead sponsor

Jozef Stefan Institute

Other

Collaborators

  • University of Ljubljana
  • University of Ljubljana, Faculty of Medicine

Registry information

Official study title

Investigating the Effects of a 10-day Heat Acclimation and Exercise Intervention on Physiological Adaptations and Cross-tolerance in Women

Acronym: FemAdapt_HOT

Important dates

Study start
2024
Primary completion
2024
Study completion
2024
First posted
Aug 28, 2024
Registry last updated
Aug 28, 2024

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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