An interventional study of Simulated work in the heat with no cooling during rest breaks and Simulated work in the heat with partial cooling during rest breaks in Body Temperature Changes, Heat Stress and Heat Exposure, sponsored by University of Ottawa. Completed at 1 site in Canada. Open to male participants aged 18 Years to 69 Years, including healthy volunteers. Per ClinicalTrials.gov, last updated 2025-06-17.
Sponsored by University of Ottawa · Not applicable, Interventional, and Basic science
Occupational heat stress directly threatens workers' ability to live healthy and productive lives. Heat exposed workers are at an elevated risk of experiencing impaired work performance and cognitive function leading to a greater risk of work-related injuries which includes traumatic injury and a myriad of pathophysiological conditions (e.g., heat stroke, acute kidney injury, adverse cardiovascular events). To mitigate the adverse health effects of occupational heat stress, safety organizations recommend upper limits for heat stress, typically defined by a worker's metabolic rate and the prevailing wet-bulb globe temperature (WBGT). In instances where the heat load created by the combination of work intensity, environment, and clothing worn exceed the upper heat stress limits (uncompensable heat stress), controls such as rest breaks are prescribed to limit increases in core temperature beyond recommended limits. While workers are encouraged to find shelter from the heat during a rest break, it is not always possible or feasible. Typically, workers may rest while remaining exposed to the heat, recover in a shaded area or rest in an air-conditioned room or vehicle. However, the effectiveness of these cooling strategies in mitigating the level of physiological strain experienced by the worker during prolonged work in a hot environment remains unclear. In this project, the investigators will assess the efficacy of the different cooling strategies in preventing excursions in core temperature beyond recommended limits (38.0°C) following the initial stay time for moderate-intensity work in hot ambient conditions (WBGT of 29°C; represents hot outdoor conditions experienced by workers in summers in Ontario, Canada) in context of the prescribed American Conference of Governmental Industrial Hygienists (ACGIH) work-to-rest allocation for unacclimated adults. On three separate days, participants will walk on a treadmill at a fixed metabolic rate of 200 W/m2 until core temperature reaches and/or exceeds 38.0°C or until volitional fatigue. Thereafter, participants will complete an additional 180 min work bout employing the recommended ACGIH work-to-rest allocation of 1:3 (starting with a 45 min rest break followed by a 15 min work bout, with the cycle repeated three times over the 180 min work simulation bout) without (Control) or with cooling mitigation during each 15-min break consisting of either: i) partial cooling equivalent to sitting in a shaded space (WBGT 24°C; 31.7°C and 35% RH) such as under a tree with a light breeze (simulated with pedestal fan fixed at \~2 m/s) or ii) full cooling equivalent to sitting in air-conditioned space (e.g., room or vehicle) maintained at 22°C and 35% RH (equivalent WBGT of 16°C).
256 studies on the registry are indexed under Hyperthermia; 73 are open to participants now.
This study's enrollment of 23 is below the median of 40 across 232 interventional studies indexed under Hyperthermia.
Browse Hyperthermia studies →University of Ottawa is the lead sponsor of 125 studies on the registry; 34 are open to participants now.
Compared within Hyperthermia, this study's primary condition as ClinicalTrials.gg classifies it; the registry's first condition term is Body Temperature Changes. The counts are of registry records indexed under each term, refreshed daily. How we classify →
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Exclusion Criteria:
Underlined terms in the criteria open these too. Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Before you join, the study team explains what taking part involves — its purpose, what happens, the risks and possible benefits — and answers your questions, so you can decide freely. Consent is usually recorded on a form (the informed consent form, ICF) signed by you or, where the law allows, by someone legally authorised to decide for you.
You can keep asking questions during the study, you are told of new information that matters, and you can choose to leave at any time.
Informed consent
Before you join, the study team explains what taking part involves — its purpose, what happens, the risks and possible benefits — and answers your questions, so you can decide freely. Consent is usually recorded on a form (the informed consent form, ICF) signed by you or, where the law allows, by someone legally authorised to decide for you.
You can keep asking questions during the study, you are told of new information that matters, and you can choose to leave at any time.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Participants perform a continuous moderate-intensity work bout (metabolic rate of \~200 W/m2) until core temperature reaches 38.0°C (equivalent to a 1°C increase in body core temperature above resting levels), which is immediately followed by intermittent work using a 1:3 work-rest allocation, starting with a 45 min rest break followed by a 15 min work bout for an additional 180-min of work without cooling.
Other: Simulated work in the heat with no cooling during rest breaks
Participants perform a continuous heavy-intensity work bout (metabolic rate of \~200 W/m2) until core temperature reaches 38.0°C (equivalent to a 1°C increase in body core temperature above resting levels), which is immediately followed by intermittent work using a 1:3 work-rest allocation, starting with a 45 min rest break followed by a 15 min work bout for an additional 180-min of work with partial cooling equivalent to sitting in a shaded space (WBGT 24°C; 31.7°C and 35% RH) such as under a tree with a light breeze (simulated with pedestal fan fixed at \~2 m/s).
Other: Simulated work in the heat with partial cooling during rest breaks
Participants perform a continuous heavy-intensity work bout (metabolic rate of \~200 W/m2) until core temperature reaches 38.0°C (equivalent to a 1°C increase in body core temperature above resting levels), which is immediately followed by intermittent work using a 1:3 work-rest allocation, starting with a 45 min rest break followed by a 15 min work bout for an additional 180-min of work with full cooling equivalent to sitting in air-conditioned space (e.g., room or vehicle) maintained at 22°C and 35% RH (equivalent WBGT of 16°C).
Other: Simulated work in the heat with full cooling during rest breaks
Young and older adults will not undergo cooling during rest breaks applied during the implementation of work-rest allocations over the duration of a 180-min work period following a continuous work bout to 38.0°C (equivalent to a 1°C increase in body core temperature above resting levels).
Young and older adults will not undergo partial cooling during rest breaks applied during the implementation of work-rest allocations over the duration of a 180-min work period following a continuous work bout to 38.0°C (equivalent to a 1°C increase in body core temperature above resting levels).
Young and older adults will not undergo full cooling during rest breaks applied during the implementation of work-rest allocations over the duration of a 180-min work period following a continuous work bout to 38.0°C (equivalent to a 1°C increase in body core temperature above resting levels).
Initial stay time
Total continuous work time to achieve an initial absolute increase in core temperature of 38°C (equivalent to a 1°C increase in body core temperature above resting levels) (note: in instances where a participant voluntarily terminates work prematurely before the absolute core temperature of ≥38°C (or relative increase of ≥1°C) is achieved or the absolute core temperature is \<38°C (or relative increase of \<1°C), the time of termination or end of the work bout will be taken as the initial stay time respectively).
Time frame: End of continuous work bout as defined when core temperature reaches 38.0°C or when the maximum of 240 minutes of continuous exercise is achieved
Average core temperature during work-rest allocations
Average core temperature following initial stay time
Time frame: Period of work-rest allocations over a 180 minute following the initial stay time
Heart rate at initial stay time
Heart rate at the initial increase in absolute core temperature of 38°C (or relative increase of 1°C)
Time frame: End of continuous work bout as defined when core temperature reaches 38.0°C or when the maximum of 240 minutes of continuous exercise is achieved
Average heart rate during work-rest allocations
Average heart rate following initial stay time
Time frame: Period of work-rest allocations over a 180 minute following the initial stay time
Skin temperature at initial stay time
Skin temperature measured at the initial increase in absolute core temperature of 38°C (or relative increase of 1°C)
Time frame: End of continuous work bout as defined when core temperature reaches 38.0°C or when the maximum of 240 minutes of continuous exercise is achieved
Average skin temperature during work-rest allocations
Average heart rate following initial stay time
Time frame: Period of work-rest allocations over a 180 minute following the initial stay time
Thermal comfort scale at initial stay time
Thermal comfort assessed via a visual analog scale ("How comfortable does your body temperature feel?") (4: very uncomfortable to 1: comfortable)
Time frame: End of continuous work bout as defined when core temperature reaches 38.0°C or when the maximum of 240 minutes of continuous exercise is achieved
Thermal comfort scale during work-rest allocations
Thermal comfort assessed via a visual analog scale ("How comfortable does your body temperature feel?") (4: very uncomfortable to 1: comfortable)
Time frame: Period of work-rest allocations over a 180 minute following the initial stay time
Thirst sensation scale at initial stay time
Assessed via a visual analog scale ("How thirsty are you?") (9: very, very thirsty to 1: Not thirsty at all)
Time frame: End of continuous work bout as defined when core temperature reaches 38.0°C or when the maximum of 240 minutes of continuous exercise is achieved
Thirst sensation scale during work-rest allocations
Assessed via a visual analog scale ("How thirsty are you?") (9: very, very thirsty to 1: Not thirsty at all)
Time frame: Period of work-rest allocations over a 180 minute following the initial stay time
Rating of Perceived Exertion at initial stay time
Perceived exertion assessed via a self-report questionnaire upon verbal prompting (6: no exertion at all to 20: maximal exertion).
Time frame: End of continuous work bout as defined when core temperature reaches 38.0°C or when the maximum of 240 minutes of continuous exercise is achieved
Rating of Perceived Exertion during work-rest allocations
Perceived exertion assessed via a self-report questionnaire upon verbal prompting (6: no exertion at all to 20: maximal exertion).
Time frame: Period of work-rest allocations over a 180 minute following the initial stay time
Orthostatic Intolerance Symptoms Assessment
Cumulative sum of scores on 6 questions asking participant to rank symptoms associated with orthostatic intolerance. All symptoms scored on a scale from 0 (none) to 10 (worst possible) and include feelings of: (1) "dizziness, lightheadedness, feeling faint, or feeling like you might black out"; (2) "Problems with vision (blurring, seeing spots, tunnel vision, etc.)"; (3) "Weakness"; (4) "Fatigue"; (5) "Trouble concentrating"; and (6) "Head and neck discomfort"
Time frame: At the end of the 180 minute work-rest allocations
Ran from Sep 2024 to primary completion in Mar 2025, 6 months.
Of 103 non-industry interventional studies with no phase under Hyperthermia, half reached primary completion within 18 months of starting (the median), counting those still running; a quarter within 7 and three quarters within 30. This study's 6 months is below that.
Counting every sponsor, half of 108 studies reached it within 18 months; a quarter within 7 and three quarters within 30.
How these figures are worked out, and which studies are left out of them.
This study is completed, as verified in Jun 2025. You cannot join it, but the record below documents what was studied.
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