Recruiting

Heat Exposure

Sponsor:

University of Ottawa

Code:

NCT07847437

Conditions

Body Temperature Changes

Heat Stress

Heat Exposure

Heat Fatigue

Work Related Stress

Eligibility Criteria

Sex: Male

Age: 45 - 65

Healthy Volunteers: Accepted

Interventions

Constant Heat Exposure

Progressively Increasing Heat Exposure

Study Details

Brief summary:

Occupational heat-stress guidelines are commonly based on the level of environmental heat exposure and are largely derived from studies conducted under constant environmental conditions. However, outdoor workers are typically exposed to dynamic conditions, with environmental heat often increasing progressively from morning to afternoon. Consequently, workers may experience substantially different patterns of heat exposure across the workday even when average daily heat exposure is equivalent. It remains unclear whether the temporal pattern of heat exposure influences the amount of work that can be performed or the physiological strain experienced during a workday. Understanding these responses is important for determining whether occupational heat-stress guidelines developed under constant laboratory conditions adequately protect workers exposed to progressively changing environmental conditions.

The primary objective of this study is to determine whether the temporal pattern of heat exposure influences work performed and physiological heat strain during a simulated occupational workday in healthy middle-aged and older men. Participants will complete two 9-hour simulated workdays consisting of a 4-hour morning work period, a 1-hour lunch break, and a 4-hour afternoon work period. During one trial, wet-bulb globe temperature (WBGT) will remain constant at 28°C throughout the workday, whereas during the other trial, WBGT will progressively increase from morning to afternoon to simulate the changing environmental conditions of a typical hot summer workday. Both trials will have the same mean daily WBGT of 28°C. Participants will perform moderate-intensity treadmill exercise, and measures including total work performed, core temperature, heart rate, and time to the initial stay-time threshold will be assessed to determine whether constant and progressively increasing heat exposures produce different physiological and work-performance responses across the workday.

Conditions

Body Temperature Changes

Heat Stress

Heat Exposure

Heat Fatigue

Work Related Stress

Study ID

NCT07847437

Start date

Oct 22, 2026

Status verified date

Nov, 2026

Completion date

Aug 31, 2027

Anticipated

Primary completion date

Jun 30, 2027

Anticipated

Eligibility Criteria

Eligibility Criteria

Sex: Male

Age: 45 - 65

Healthy Volunteers: Accepted

Inclusion Criteria:

  • 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)

Exclusion Criteria:

  • Are regularly exposed to hot environments (e.g., occupational heat exposure)
  • 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

Study Design

Enrollment

14 participants

Anticipated

Allocation

Randomized

Intervention Model

Crossover

Primary purpose

Basic Science

Interventions and Outcome Measures

Arms

experimental: Constant Heat Exposure

Participants will complete a 9-hour simulated occupational workday consisting of a 4-hour morning work period, a 1-hour seated lunch-recovery period, and a 4-hour afternoon work period. Wet-bulb globe temperature (WBGT) will remain constant at 28°C throughout the workday. During each work period, participants will perform moderate-intensity treadmill walking at a metabolic heat production of approximately 200 W·m-2. Participants will initially work continuously until reaching the initial stay-time threshold, defined as a core temperature of 38.0°C or an increase of 1.0°C above pre-work baseline, whichever occurs first. Thereafter, participants will complete 45-min work and 15-min seated rest cycles for the remainder of the work period.

experimental: Progressively Increasing Heat Exposure

Participants will complete a 9-hour simulated occupational workday consisting of a 4-hour morning work period, a 1-hour seated lunch-recovery period, and a 4-hour afternoon work period. WBGT will progressively increase from morning to afternoon to simulate the changing environmental conditions of a hot summer workday, while maintaining a mean daily WBGT of 28°C. During each work period, participants will perform moderate-intensity treadmill walking at a metabolic heat production of approximately 200 W·m-2. Participants will initially work continuously until reaching the initial stay-time threshold, defined as a core temperature of 38.0°C or an increase of 1.0°C above pre-work baseline, whichever occurs first. Thereafter, participants will complete 45-min work and 15-min seated rest cycles for the remainder of the work period.

Interventions

Constant Heat Exposure

Participants complete a simulated occupational workday under constant environmental conditions, with WBGT maintained at 28°C throughout the morning and afternoon work periods.

Progressively Increasing Heat Exposure

Participants complete a simulated occupational workday in which WBGT progressively increases from morning to afternoon while maintaining a mean daily WBGT of 28°C.

Primary outcome measure

  • Total work performed [ Time Frame: From the start to the end of the morning and afternoon work periods during each experimental trial (0-4 hours and 5-9 hours after the start of the trial, respectively). ]

Central Contacts and Locations

Central contacts

Glen P Kenny, PhD

6135625800gkenny@uottawa.ca

Locations

University of Ottawa

Recruiting

Ottawa, Ontario, Canada, K1N 6N5

Contacts

Glen P Kenny, PhD

613-562-5800gkenny@uottawa.ca

More Information

Sponsor

University of Ottawa

Last update posted

Nov 12, 2026

Last verified

Nov, 2026

Keywords

  • Heat Strain
  • Thermoregulation
  • Core Temperature
  • Occupational Heat Stress
  • Physical Activity
  • Hyperthermia

Trial information was received from ClinicalTrials.gov and was last updated on 2026-11-13. This information was provided to ClinicalTrials.gov by University of Ottawa on 2026-11-12. Recruitment status is synced daily from ClinicalTrials.gov and may not reflect the sponsor's current status. Confirm during your call.