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

NCT05847712 | Completed

• 1 other identifier: HEPRU 2023-03
• Study Type: interventional
• Target: 60
• Locations: 1 country
• Sites: 1

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 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, this information is limited to a single work bout and does not consider a second work bout preceded by an extended rest period (e.g., lunch) or next day effects. This is a key consideration, as prolonged work in the heat has been shown to cause next-day impairments in heat dissipation in older men. Further, it remains unclear if the application of the prescribed ACGIH 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). This project will address these knowledge gaps by determining if refinements in initial stay times for moderate-intensity work (represents the average work effort of physically demanding occupations) in the heat (26°C wet-bulb globe temperature) may be required for young and older adults for i) a second work bout that is preceded by an extended rest period such as a lunch break, and ii) a work bout performed on the next day. This includes assessing the efficacy of the prescribed ACGIH work-rest allocations to mitigate increases in core temperature beyond safe limits (\>38.0°C, equivalent to a \>1°C increase in body core temperature above resting levels) during these work periods. Given the known sex-differences in heat loss that can modulate core temperature regulation during an exercise-heat stress, the investigators will conduct separate analysis to identify modulating effects of biological sex on the initial stay times and effectiveness of the work-rest allocation as a heat-alleviation control.

Conditions

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

Keywords

Heat exposure; Heat strain; Body temperature; Thermoregulation; Occupational heat stress; Uncompensable heat stress; Aging; Sex

Outcome Measures

Primary Outcomes (6)

• 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).

  End of first (morning day 1) continuous work bout

• 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).

  End of second (afternoon day 1) continuous work bout

• 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).

  End of third (morning day 2) continuous work bout

• Average core temperature

  Average core temperature over final 2-hours of each work bout

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

• Average core temperature

  Average core temperature following initial stay time

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

• Average core temperature

  Average core temperature following initial stay time

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

Secondary Outcomes (57)

• Heart rate at initial stay time

  End of first (morning day 1) continuous work bout

• Heart rate at initial stay time

  End of second (afternoon day 1) continuous work bout

• Heart rate at initial stay time

  End of third (morning day 2) continuous work bout

• Average heart rate

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

• Average heart rate

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

Study Arms (2)

Younger adults

EXPERIMENTAL

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

Other: Simulated work in the heat

Older adults

EXPERIMENTAL

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

Other: Simulated work in the heat

Interventions

Simulated work in the heat OTHER

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 3:1 work-rest allocation, starting with a 15 min rest break followed by a 45 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; Younger adults

Eligibility Criteria

• Age: 18 Years - 69 Years
• Sex: all
• Healthy Volunteers: Yes
• Age Groups: Adult (18-64), Older Adult (65+)

You may qualify if:

• 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

You may not qualify if:

• 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)

Sponsors & Collaborators

• University of Ottawa: lead

Study Sites (1)

University of Ottawa

Ottawa, Ontario, K1N6N5, Canada

Location

MeSH Terms

Conditions

Heat Stress Disorders; Motor Activity; Coitus

Condition Hierarchy (Ancestors)

Wounds and Injuries; Behavior; Sexual Behavior

Study Officials

• Glen P Kenny, PhD

  University of Ottawa

  PRINCIPAL INVESTIGATOR

Study Design

• Study Type: interventional
• Phase: not applicable
• Allocation: NON RANDOMIZED
• Masking: SINGLE
• Who Masked: OUTCOMES ASSESSOR
• Masking Details: Data will be blinded prior to analysis
• Purpose: BASIC SCIENCE
• Intervention Model: PARALLEL
• Sponsor Type: OTHER
• Responsible Party: PRINCIPAL INVESTIGATOR
• PI Title: Full Professor, University Research Chair

Study Record Dates

• First Submitted: April 27, 2023
• First Posted: May 8, 2023
• Study Start: June 8, 2023
• Primary Completion: July 12, 2024
• Study Completion: July 12, 2024
• Last Updated: August 6, 2024

Record last verified: 2024-08

Data Sharing

• IPD Sharing: Will share
• Shared Documents: STUDY PROTOCOL, SAP, ANALYTIC CODE
• Time Frame: Following publication of the main study report(s)
• Access Criteria: Approved analysis plan and signed access agreement

Locations

CA (1)