AzTrials
AzTrials

Core TemperatureNCT06543719

Initial Stay Times and Heat Mitigation Controls for Uncompensable Occupational Heat Stress - Part II

A study testing Simulated work in the heat in people with Core Temperature and Heat Stress, Exertional, run by University of Ottawa at 1 site in Canada.

Completed

Finished. The study has ended and is not enrolling. Results may be posted on the official record.

Official record
Search all trials

Trial summary

Workplaces rely on upper heat stress limits provided by the American Conference of Governmental Industrial Hygienists (ACGIH) to manage the health and safety of workers in hot environments. Read more about this study

Who is it for?
Ages 18 to 69 years, men onlyHealthy volunteers can take part
What is being tested?
Simulated work in the heat
Could I receive a placebo?
No, everyone receives an active treatment
How many people
21 participants
Where
1 siteCanada
Study dates
25 Jul 2024to 28 Nov 2024
Phase
Interventional
Are there results?
None posted in the registry

Key requirements

Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.

  • Ages 18 to 69 years
  • Men only
  • Healthy volunteers accepted
  • Adult, Older adult

Who may be able to join

  • young (18-30 years) and older adults (50-69 years)
  • habitually active, not endurance trained (<2 sessions per week, <150 minutes per week)
  • non-smoking
  • English or French speaking
  • ability to provide informed consent

Who cannot join

  • pre-existing health conditions (e.g., diabetes, hypertension)
  • use of medication deemed to significantly modulate thermoregulatory function and heat tolerance (e.g., antidepressants, antihistamines, diuretics)
  • engaged in jobs and/or activities that involve frequent exposure to hot environments (e.g., regular sauna use)

Trial locations and contacts

1 site in 1 country.

Canada1 site
  • University of Ottawa

    Ottawa, Ontario, K1N 6N5

Other trials in Canada

About this study

Official title: Safe Maximum Work Times and the Effectiveness of Work-rest Allocations in Mitigating Increases in Core Temperature During and on the Day Following Prolonged Heavy-Intensity Work in the Heat in Young and Older Workers

Workplaces rely on upper heat stress limits provided by the American Conference of Governmental Industrial Hygienists (ACGIH) to manage the health and safety of workers in hot environments. This is primarily achieved by interspersing work with rest periods, the length of which is dictated by environmental conditions and work intensity, to maintain core temperature at or below 38.0°C (equivalent to a 1°C increase in body core temperature above resting levels). However, these guidelines employ a "one size fits all" approach to exposure limits that does not consider individual variation (e.g., age) between workers. Moreover, they fail to provide direction on the safe, initial stay times before these heat-mitigation controls should be employed (i.e., rest breaks) in conditions exceeding upper heat stress limits. While recent work has generated estimates of the initial stay times for young to older men before heat-mitigation controls are required for moderate-intensity work, information on initial stay times for heavy-intensity work remains to be assessed. This project will assess the initial stay times for heavy-intensity work for a single work bout as well as for a second work bout that is preceded by an extended rest period such as a lunch break and a work bout performed on the next day to determine if refinements in initial stay times across these periods may be required. Further, the investigators will evaluate if the application of recommended work-rest allocations thereafter would alleviate increases in core temperature for the duration of the work period (e.g., start of shift versus post-lunch period). Given the known age-differences in heat loss that can modulate core temperature regulation during an exercise-heat stress, the investigators will assess responses response in young and older adults.

Being tested
Simulated work in the heat
Keywords
Heat exposure, Heat strain, Body temperature, Thermoregulation, Occupational heat stress, Uncompensable heat stress, Aging
Medical subject headings
Heat Stress Disorders, Motor Activity

What participants receive

What participants receive. In a randomised study each person is assigned to one group by chance.

  • Simulated work in the heatOther

    Participants perform a continuous heavy-intensity work bout (metabolic rate of ~260 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 1:1 work-rest allocation, starting with a 30 min rest break followed by a 30 min work bout for a total work duration of ~240 min. The work protocol is performed in the morning of day 1, and repeated in a post-lunch work period (i.e., afternoon of day 1) and on the morning of the next day (i.e., morning of day 2).

Study groups in NCT06543719
Study groupRoleWhat they receive
Younger adults.ExperimentalAdults aged 18-30 years with no pre-existing health conditions
Receives: Other: Simulated work in the heat
Older adults. Adults aged 50-69 with no pre-existing health conditionsExperimentalAdults aged 50-69 with no pre-existing health conditions
Receives: Other: Simulated work in the heat

What is being measured

The primary outcome is the main question the study is designed to answer.

  1. 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).

    Measured: End of first (morning day 1) continuous work bout

  2. 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).

    Measured: End of second (afternoon day 1) continuous work bout

  3. 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).

    Measured: End of third (morning day 2) continuous work bout

  4. Average core temperature

    Average core temperature following initial stay time

    Measured: Period of work-rest allocations following initial stay time for morning day 1

  5. Average core temperature

    Average core temperature following initial stay time

    Measured: Period of work-rest allocations following initial stay time for afternoon day 1

  6. Average core temperature

    Average core temperature following initial stay time

    Measured: Period of work-rest allocations following initial stay time for morning of day 2

Secondary outcomes (54)
  1. 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)

    Measured: End of first (morning day 1) continuous work bout

  2. 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)

    Measured: End of first (afternoon day 1) continuous work bout

  3. 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)

    Measured: End of first (morning day 2) continuous work bout

  4. Average heart rate

    Average heart rate following initial stay time

    Measured: Period of work-rest allocations following initial stay time for morning of day 1

  5. Average heart rate

    Average heart rate following initial stay time

    Measured: Period of work-rest allocations following initial stay time for afternoon of day 1

  6. Average heart rate

    Average heart rate following initial stay time

    Measured: Period of work-rest allocations following initial stay time for morning of day 2

  7. Skin temperature at initial stay time

    Skin temperature (4 sites) measured at the initial increase in absolute core temperature of 38°C (or relative increase of 1°C)

    Measured: End of first (morning day 1) continuous work bout

  8. Skin temperature at initial stay time

    Skin temperature (4 sites) measured at the initial increase in absolute core temperature of 38°C (or relative increase of 1°C)

    Measured: End of first (afternoon day 1) continuous work bout

  9. Skin temperature at initial stay time

    Skin temperature (4 sites) measured at the initial increase in absolute core temperature of 38°C (or relative increase of 1°C)

    Measured: End of first (morning day 2) continuous work bout

  10. Average skin temperature

    Average heart rate following initial stay time

    Measured: Period of work-rest allocations following initial stay time for morning of day 1

  11. Average skin temperature

    Average heart rate following initial stay time

    Measured: Period of work-rest allocations following initial stay time for afternoon of day 1

  12. Average skin temperature

    Average heart rate following initial stay time

    Measured: Period of work-rest allocations following initial stay time for morning of day 2

  13. Systolic blood pressure

    Arterial blood pressure measured via automated oscillometry

    Measured: End of first (morning day 1) work period

  14. Systolic blood pressure

    Arterial blood pressure measured via automated oscillometry

    Measured: End of second (afternoon day 1) work period

  15. Systolic blood pressure

    Arterial blood pressure measured via automated oscillometry

    Measured: End of third (morning day 2) work period

  16. Diastolic blood pressure

    Arterial blood pressure measured via automated oscillometry

    Measured: End of first (morning day 1) work period

  17. Diastolic blood pressure

    Arterial blood pressure measured via automated oscillometry

    Measured: End of second (afternoon day 1) work period

  18. Diastolic blood pressure

    Arterial blood pressure measured via automated oscillometry

    Measured: End of third (morning day 1) work period

  19. Mean arterial pressure

    Calculated as 1/3 * systolic blood pressure + 2/3 * diastolic blood pressure

    Measured: End of first (morning day 1) work period

  20. Mean arterial pressure

    Calculated as 1/3 * systolic blood pressure + 2/3 * diastolic blood pressure

    Measured: End of second (afternoon day 1) work period

  21. Mean arterial pressure

    Calculated as 1/3 * systolic blood pressure + 2/3 * diastolic blood pressure

    Measured: End of third (morning day 2) work period

  22. Rate pressure product

    Calculated as systolic blood pressure * heart rate

    Measured: End of first (morning day 1) work period

  23. Rate pressure product

    Calculated as systolic blood pressure * heart rate

    Measured: End of second (afternoon day 1) work period

  24. Rate pressure product

    Calculated as systolic blood pressure * heart rate

    Measured: End of third (morning day 2) work period

  25. Fluid consumption

    Cumulative fluid consumption calculated by weighing the participant's water intake

    Measured: End of first (morning day 1) work period

  26. Fluid consumption

    Cumulative fluid consumption calculated by weighing the participant's water intake

    Measured: End of second (afternoon day 1) work period

  27. Fluid consumption

    Cumulative fluid consumption calculated by weighing the participant's water intake

    Measured: End of third (morning day 2) work period

  28. Fluid loss

    Fluid loss calculated as the change in body mass (corrected for food/fluid consumption).

    Measured: End of first (morning day 1) work period

  29. Fluid loss

    Fluid loss calculated as the change in body mass (corrected for food/fluid consumption).

    Measured: End of second (afternoon day 1) work period

  30. Fluid loss

    Fluid loss calculated as the change in body mass (corrected for food/fluid consumption).

    Measured: End of third (morning day 2) work period

  31. Change in plasma volume

    Determined from venous blood samples

    Measured: End of first (morning day 1) work period

  32. Change in plasma volume

    Determined from venous blood samples

    Measured: End of second (afternoon day 1) work period

  33. Change in plasma volume

    Determined from venous blood samples

    Measured: End of third (morning day 2) work period

  34. Thermal comfort scale

    Thermal comfort assessed via a visual analog scale ("How comfortable does your body temperature feel?") (4: very uncomfortable to 1: comfortable)

    Measured: End of first (morning day 1) continuous work bout

  35. Thermal comfort scale

    Thermal comfort assessed via a visual analog scale ("How comfortable does your body temperature feel?") (4: very uncomfortable to 1: comfortable)

    Measured: End of second (afternoon day 1) continuous work bout

  36. Thermal comfort scale

    Thermal comfort assessed via a visual analog scale ("How comfortable does your body temperature feel?") (4: very uncomfortable to 1: comfortable)

    Measured: End of third (morning day 2) continuous work bout

  37. Thermal comfort scale

    Thermal comfort assessed via a visual analog scale ("How comfortable does your body temperature feel?") (4: very uncomfortable to 1: comfortable)

    Measured: Period of work-rest allocations following initial stay time for morning of day 1

  38. Thermal comfort scale

    Thermal comfort assessed via a visual analog scale ("How comfortable does your body temperature feel?") (4: very uncomfortable to 1: comfortable)

    Measured: Period of work-rest allocations following initial stay time for afternoon of day 1

  39. Thermal comfort scale

    Thermal comfort assessed via a visual analog scale ("How comfortable does your body temperature feel?") (4: very uncomfortable to 1: comfortable)

    Measured: Period of work-rest allocations following initial stay time for morning of day 2

  40. Thirst sensation scale

    Assessed via a visual analog scale ("How thirsty are you?") (9: very, very thirsty to 1: Not thirsty at all)

    Measured: End of first (morning day 1) continuous work bout

  41. Thirst sensation scale

    Assessed via a visual analog scale ("How thirsty are you?") (9: very, very thirsty to 1: Not thirsty at all)

    Measured: End of second (afternoon day 1) continuous work period

  42. Thirst sensation scale

    Assessed via a visual analog scale ("How thirsty are you?") (9: very, very thirsty to 1: Not thirsty at all)

    Measured: End of third (morning day 2) continuous work period

  43. Thirst sensation scale

    Assessed via a visual analog scale ("How thirsty are you?") (9: very, very thirsty to 1: Not thirsty at all)

    Measured: Period of work-rest allocations following initial stay time for morning of day 1

  44. Thirst sensation scale

    Assessed via a visual analog scale ("How thirsty are you?") (9: very, very thirsty to 1: Not thirsty at all)

    Measured: Period of work-rest allocations following initial stay time for afternoon day 2

  45. Thirst sensation scale

    Assessed via a visual analog scale ("How thirsty are you?") (9: very, very thirsty to 1: Not thirsty at all)

    Measured: Period of work-rest allocations following initial stay time for morning of day 2

  46. Rating of Perceived Exertion

    Perceived exertion assessed via a self-report questionnaire upon verbal prompting (6: no exertion at all to 20: maximal exertion).

    Measured: End of first (morning day 1) continuous work bout

  47. Rating of Perceived Exertion

    Perceived exertion assessed via a self-report questionnaire upon verbal prompting (6: no exertion at all to 20: maximal exertion).

    Measured: End of second (afternoon day 1) continuous work bout

  48. Rating of Perceived Exertion

    Perceived exertion assessed via a self-report questionnaire upon verbal prompting (6: no exertion at all to 20: maximal exertion).

    Measured: End of third (morning day 2) continuous work bout

  49. Rating of Perceived Exertion

    Perceived exertion assessed via a self-report questionnaire upon verbal prompting (6: no exertion at all to 20: maximal exertion).

    Measured: Period of work-rest allocations following initial stay time for morning of day 1

  50. Rating of Perceived Exertion

    Perceived exertion assessed via a self-report questionnaire upon verbal prompting (6: no exertion at all to 20: maximal exertion).

    Measured: Period of work-rest allocations following initial stay time for afternoon of day 1

  51. Rating of Perceived Exertion

    Perceived exertion assessed via a self-report questionnaire upon verbal prompting (6: no exertion at all to 20: maximal exertion).

    Measured: Period of work-rest allocations following initial stay time for morning of day 2

  52. 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"

    Measured: End of first (morning day 1) continuous work bout

  53. 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"

    Measured: End of second (afternoon day 1) continuous work bout

  54. 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"

    Measured: End of third (afternoon day 1) continuous work bout

Timeline

From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.

  1. First posted9 Aug 2024
  2. Study start25 Jul 2024
  3. Primary completion28 Nov 2024
  4. Study completion28 Nov 2024

Resources

More details

For doctors and researchers: how the study is designed, who runs it, and its registry IDs.

Study design
Study type
Interventional
Phase
Phase N/A
Primary purpose
Basic science
Allocation
Non-randomised
Intervention model
Parallel groups
Masking
Single blind
Who is masked
Outcomes assessor
Enrolment
21 participants (actual)
IDs, dates and publications
ClinicalTrials.gov ID
NCT06543719
Sponsor's protocol ID
HEPRU-2024-07
Status last verified
Jun 2025
First submitted
4 Aug 2024
Last updated
18 Jun 2025
Results posted
No
Data monitoring committee
No
FDA-regulated drug
No
FDA-regulated device
No

Questions about this trial

What is this clinical trial studying?

A study testing Simulated work in the heat in people with Core Temperature and Heat Stress, Exertional, run by University of Ottawa at 1 site in Canada.

The full registered description is in the About this study section and the official record.

Who may be eligible to take part?

The sponsor lists 5 inclusion and 3 exclusion criteria. Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.

Is this clinical trial currently recruiting?

The record says: finished, as of the sponsor's last update on 18 Jun 2025. Status can change between updates, so confirm with the study contact before making plans.

Where is the study taking place?

The record lists 1 site in Canada. Whether a site is taking part right now should be confirmed with that site. See every site.

What are the possible benefits and risks?

They depend on the study and the treatment, and no study can promise a benefit. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.

Are results available for this study?

The study is completed, but results are not available in the source record. That does not mean the treatment did or did not work.

How can a doctor refer a patient or contact the research team?

The record lists no contact. The official record names the sponsor, who can be asked directly. AzTrials does not enrol participants or take referrals.

What does the primary outcome measure?

Initial stay time (time frame: End of first (morning day 1) continuous work bout). The study lists 6 primary outcomes in all. It is what the study was designed to measure, not a finding.

Where can I read the original study information?
Does a listing mean the treatment is approved or proven to work?

No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.

How often is this information updated?

AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 18 Jun 2025.

Free account

Log in to keep searching

You’ve used your 3 free searches. AzTrials is free: log in or create a free account to keep searching clinical trials and save the ones you want to follow.

Create a free accountLog in