Working in the Heat at Simulated Altitude: Effects of Normobaric Hypoxia on Physiological Strain

NCT07664462 | Recruiting

• 1 other identifier: HEPRU-2026-06-B
• Study Type: interventional
• Target: 20
• Locations: 1 country
• Sites: 1

Brief Summary

Extreme heat events are becoming more frequent, intense, and prolonged, increasing the risk of heat-related illness among workers performing physically demanding work in hot environments. Occupational heat-stress guidelines use work-rest schedules to limit increases in core temperature and physiological strain, but they do not clearly define the safe maximum duration of continuous work before heat-mitigation controls should begin, known as the initial stay time. Recent work has generated initial stay time recommendations for young and older workers performing moderate-intensity work in the heat; however, these recommendations were developed under normoxic conditions. In many workplaces, heat may occur alongside additional stressors such as hypoxia, including work at altitude or in oxygen-reduced environments. Hypoxia can increase cardiovascular strain, reduce arterial oxygen saturation, and impair exercise tolerance, potentially compromising heat-stress guidance developed under normal oxygen conditions. Older workers may be especially vulnerable because of age-related reductions in thermoregulatory and cardiovascular function. It remains unclear whether hypoxia increases physiological strain during work in the heat or whether current initial stay time and recovery recommendations remain protective under combined heat and hypoxic stress. The primary objective of this study is to determine whether hypoxia increases physiological strain during moderate-intensity work in the heat in young and older males. Specifically, the study will assess whether normoxia-derived initial stay times and recovery recommendations for work at 29°C wet-bulb globe temperature (37.5°C, 35% RH) remain effective during exposure to 14% inspired oxygen, simulating approximately 3000 m altitude. Healthy young and older males will complete two simulated occupational heat exposures: heat alone and heat plus hypoxia. Participants will perform moderate-intensity treadmill work based on age-specific initial stay times, followed by prescribed work-rest cycles and seated recovery. Core temperature, cardiovascular strain, oxygen saturation, skin temperature, hydration status, perceptual responses, mood, environmental stress symptoms, and cognitive function will be assessed to determine whether hypoxia modifies responses to work in the heat. Findings will help determine whether occupational heat-stress guidance requires refinement for workers exposed to combined heat and hypoxic stress.

Conditions

Heat Stress; Heat Exposure; Heat Fatigue; Hypoxia, Altitude; Body Temperature Changes; Work Related Stress; Physiological Stress

Keywords

Heat Strain; Thermoregulation; Exercise; Simulated altitude; Core temperature; Occupational Heat Stress; Aging; Hypoxia; Hyperthermia

Outcome Measures

Primary Outcomes (1)

• Total work volume

  Total work completed during the 240-minute work bout. The work period consists of an initial continuous walking phase to a core temperature 38.0°C or 1°C increase above baseline resting, followed by intermittent work-rest cycles.

  During the 240-minute work period

Secondary Outcomes (30)

• Time to core temperature of 38.0°C

  During the 240-minute work period

• Time to 1.0°C increase in core temperature

  During the 240-minute work period

• Average core temperature during work/rest cycles

  During the 240-minute work period

• Heart rate at core temperature of 38.0°C

  During the 240-minute work period

• Heart rate at 1.0°C increase in core temperature

  During the 240-minute work period

Study Arms (2)

Normoxic exposure

EXPERIMENTAL

Participants complete a simulated moderate-intensity occupational heat exposure protocol in a hot environment (37.5°C, 35% RH) under normoxic conditions. Participants walk on a treadmill until they reach their initial stay time, followed by prescribed work-rest cycles and seated recovery.

Other: Simulated Occupational heat exposure under normoxic conditions

Hypoxic exposure

EXPERIMENTAL

Participants complete a simulated moderate-intensity occupational heat exposure protocol in a hot environment (37.5°C, 35% RH) with an added hypoxic exposure equivalent to 14% inspired oxygen. Participants walk on a treadmill until they reach their initial stay time, followed by prescribed work-rest cycles and seated recovery.

Other: Simulated Occupational heat exposure under hypoxic conditions

Interventions

Simulated Occupational heat exposure under normoxic conditions OTHER

Participants complete a simulated moderate-intensity occupational heat exposure protocol involving treadmill walking in a hot environment (37.5°C, 35% RH) under normoxic conditions (\~20.9% inspired oxygen). Participants walk until they reach their initial stay time, followed by prescribed work-rest cycles and seated recovery.

Normoxic exposure

Simulated Occupational heat exposure under hypoxic conditions OTHER

Participants complete a simulated moderate-intensity occupational heat exposure protocol involving treadmill walking in a hot environment (37.5°C, 35% RH) with an added hypoxic exposure equivalent to 14% inspired oxygen. Participants walk until they reach their initial stay time, followed by prescribed work-rest cycles and seated recovery.

Hypoxic exposure

Eligibility Criteria

• Age: 18 Years - 70 Years
• Sex: male
• Healthy Volunteers: No
• Age Groups: Adult (18-64), Older Adult (65+)

You may qualify if:

• Are male.
• Do not smoke or have been smoke free for at least 5 years.
• English or French speaking.
• Ability to provide informed consent.
• Are physically active (engage in exercise at least 2 times per week for ≥30 minutes)

You may not qualify if:

• Are regularly exposed to hot environments (e.g., occupational heat exposure)
• Are regularly exposed to hypoxic environments (e.g., high altitudes)
• Experience claustrophobia or discomfort in enclosed environments
• Episode(s) of severe hypoglycemia (requiring the assistance of another person) within the previous year, or inability to sense hypoglycemia (hypoglycemia unawareness).
• Serious complications related to diabetes (gastroparesis, renal disease, uncontrolled hypertension, severe autonomic neuropathy).
• Uncontrolled hypertension - BP \>150 mmHg systolic or \>95 mmHg diastolic in a sitting position.
• Restrictions in physical activity due to disease (e.g. intermittent claudication, renal impairment, active proliferative retinopathy, unstable cardiac or pulmonary disease, disabling stroke, severe arthritis, etc.).
• Use of or changes in medication judged by the patient or investigators to make participation in this study inadvisable.
• Cardiac abnormalities identified during screening

Sponsors & Collaborators

• University of Ottawa: lead

Study Sites (1)

University of Ottawa

Ottawa, Ontario, K1N 6N5, Canada

RECRUITING

MeSH Terms

Conditions

Body Temperature Changes; Heat Stress Disorders; Altitude Sickness; Occupational Stress; Motor Activity; Hypoxia; Hyperthermia

Condition Hierarchy (Ancestors)

Signs and Symptoms; Pathological Conditions, Signs and Symptoms; Wounds and Injuries; Respiration Disorders; Respiratory Tract Diseases; Occupational Diseases; Stress, Psychological; Behavioral Symptoms; Behavior; Signs and Symptoms, Respiratory

Study Officials

• Glen P Kenny, PhD

  University of Ottawa

  PRINCIPAL INVESTIGATOR

Central Study Contacts

Glen P Kenny, PhD

CONTACT

6135625800; gkenny@uottawa.ca

Study Design

• Study Type: interventional
• Phase: not applicable
• Allocation: RANDOMIZED
• Masking: SINGLE
• Who Masked: OUTCOMES ASSESSOR
• Purpose: BASIC SCIENCE
• Intervention Model: CROSSOVER
• Sponsor Type: OTHER
• Responsible Party: PRINCIPAL INVESTIGATOR
• PI Title: Full Professor, University Research Chair

Study Record Dates

• First Submitted: June 17, 2026
• First Posted: June 24, 2026
• Study Start: June 17, 2026
• Primary Completion (Estimated): December 31, 2026
• Study Completion (Estimated): February 28, 2027
• Last Updated: July 14, 2026

Record last verified: 2026-07

Locations

CA (1)