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

NCT ID: NCT06543719

Last Updated: 2025-06-18

Basic Information

• Recruitment Status: COMPLETED
• Clinical Phase: NA
• Total Enrollment: 21 participants
• Study Classification: INTERVENTIONAL
• Study Start Date: 2024-07-25
• Study Completion Date: 2024-11-28

Brief 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. 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.

Conditions

Core Temperature; Heat Stress, Exertional; Heat Fatigue; Exercise

Study Design

• Allocation Method: NON_RANDOMIZED
• Intervention Model: PARALLEL
• Primary Study Purpose: BASIC_SCIENCE
• Blinding Strategy: SINGLE

Study Groups

Younger adults.

Adults aged 18-30 years with no pre-existing health conditions

Group Type: EXPERIMENTAL

Simulated work in the heat

Intervention Type: OTHER

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).

Older adults. Adults aged 50-69 with no pre-existing health conditions

Adults aged 50-69 with no pre-existing health conditions

Group Type: EXPERIMENTAL

Simulated work in the heat

Intervention Type: OTHER

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).

Interventions

Simulated work in the heat

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).

Intervention Type: OTHER

Eligibility Criteria

Inclusion Criteria

• 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

Exclusion Criteria

• 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)

• Minimum Eligible Age: 18 Years
• Maximum Eligible Age: 69 Years
• Eligible Sex: MALE
• Accepts Healthy Volunteers: Yes

Sponsors

University of Ottawa

OTHER

Sponsor Role: lead

Responsible Party

Glen P. Kenny

Principal investigator

Responsibility Role: PRINCIPAL_INVESTIGATOR

Locations

University of Ottawa

Ottawa, Ontario, Canada

Countries

Canada

Other Identifiers

HEPRU-2024-07

Identifier Type: -

Identifier Source: org_study_id