Consecutive Occupational Heat Exposure With and Without Overnight Cooling

NCT07656519 | Not Yet Recruiting

• 1 other identifier: HEPRU-2026-06-A
• Study Type: interventional
• Target: 10
• Locations: 1 country
• Sites: 1

Brief Summary

Extreme heat events are becoming more frequent, intense, and prolonged, increasing the risk of heat-related illness among workers exposed to hot environments. Current occupational heat-stress guidelines are designed to limit excessive increases in core body temperature and physiological strain during work in the heat through the use of work-rest schedules. However, these guidelines are largely based on single-day heat exposures and assume that workers recover in cool indoor environments between shifts. During heat events, many workers may instead recover in homes or accommodations that remain overheated, particularly in the absence of air conditioning. Inadequate overnight cooling may impair the body's ability to dissipate heat, increase physiological strain, and reduce tolerance to heat exposure on subsequent workdays. Older adults may be especially vulnerable due to age-related impairments in heat-loss capacity. To date, the effects of recovering in an overheated indoor environment on physiological strain and thermoregulatory function during repeated occupational heat exposure remain poorly understood, limiting the development of evidence-based recommendations to protect workers during prolonged heat events. The primary objective of this study is to determine whether overnight recovery in an overheated indoor environment increases physiological strain during repeated occupational heat exposure in older adults. Specifically, investigators will assess whether recovery at the recently proposed upper indoor temperature limit of 26°C and 45% relative humidity (RH) (PMID: 38329752) is sufficient to attenuate elevations in core temperature during subsequent work in the heat compared with recovery in an overheated indoor environment (31°C, 45% RH) representative of conditions commonly experienced during extreme heat events. Healthy older adults will complete two consecutive days and nights of simulated moderate-intensity occupational heat exposure, with overnight recovery occurring in either the 26°C or 31°C condition. Measures of core temperature, cardiovascular strain, heat-loss capacity, hydration status, sleep quality, cognitive function, mood, and perceptual responses will be assessed to determine the impact of overnight recovery conditions on responses to repeated heat exposure. Whole-body heat-loss capacity will also be evaluated before and after the exposure protocol as assessed during incremental, intermittent exercise protocol performed in an air calorimeter.

Conditions

Body Temperature Changes; Heat Stress; Heat Exposure; Heat Fatigue; Work Related Stress; Physiological Stress

Keywords

Heat Strain; Thermoregulation; Exercise; Core temperature; Occupational heat stress; Aging; Heat wave; Sleep; Hyperthermia

Outcome Measures

Primary Outcomes (1)

• Total work volume.

  Total work completed during the 240-minute work protocol performed in the morning and afternoon work periods, expressed as cumulative minutes of work performed over the two consecutive work days. The work period consists of an initial continuous walking phase to a core temperature 38.0°C or 1°C increase above baseline resting (as measured prior to the start of the 2-day work protocol), followed by intermittent work-rest cycles. The morning and afternoon work periods are separated by a 1-hour recovery period.

  During each 240-minute morning and afternoon work bout on Day 1 and Day 2.

Secondary Outcomes (44)

• Time to core temperature of 38.0°C

  During each 240-minute morning and afternoon work bout on Day 1 and Day 2.

• Time to 1.0°C increase in rectal temperature

  During each 240-minute morning and afternoon work bout on Day 1 and Day 2.

• Average core temperature during work/rest cycles

  During each 240-minute morning and afternoon work bout on Day 1 and Day 2.

• Heart rate at core temperature of 38.0°C

  Each morning and afternoon work bout on Day 1 and Day 2.

• Heart rate at 1.0°C increase in core temperature

  Each morning and afternoon work bout on Day 1 and Day 2.

Study Arms (2)

Recovery at recommended indoor temperature limit

EXPERIMENTAL

Participants complete a 2-day, 2-night simulated occupational heat exposure protocol consisting of daytime work in a hot environment (37.5°C, 35% RH) and overnight recovery (18:30-08:00) at the recommended upper indoor temperature limit (26°C, 45% RH).

Other: Simulated occupational heat exposure with recovery at recommended indoor temperature limit

Recovery in an overheated indoor environment

EXPERIMENTAL

Participants complete a 2-day, 2-night simulated occupational heat exposure protocol consisting of daytime work in a hot environment (37.5°C, 35% RH) and overnight recovery (18:30-08:00) in an overheated indoor environment (31°C, 45% RH).

Other: Simulated occupational heat exposure with recovery in an overheated indoor environment

Interventions

Simulated occupational heat exposure with recovery at recommended indoor temperature limit OTHER

Participants complete a 2-day, 2-night simulated occupational heat exposure protocol involving daytime work in a hot environment (37.5°C, 35% RH) and overnight recovery (18:30-08:00) at the recommended upper indoor temperature limit (26°C, 45% RH).

Recovery at recommended indoor temperature limit

Simulated occupational heat exposure with recovery in an overheated indoor environment OTHER

Participants complete a 2-day, 2-night simulated occupational heat exposure protocol involving daytime work in a hot environment (37.5°C, 35% RH) and overnight recovery (18:30-08:00) in an overheated indoor environment (31°C, 45% RH).

Recovery in an overheated indoor environment

Eligibility Criteria

• Age: 50 Years - 70 Years
• Sex: male
• Healthy Volunteers: Yes
• Age Groups: Adult (18-64), Older Adult (65+)

You may qualify if:

• 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)

You may not qualify if:

• 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

Sponsors & Collaborators

• University of Ottawa: lead

Study Sites (1)

University of Ottawa

Ottawa, Ontario, K1N 6N5, Canada

Location

Related Publications (1)

• Meade RD, Akerman AP, Notley SR, Kirby NV, Sigal RJ, Kenny GP. Effects of Daylong Exposure to Indoor Overheating on Thermal and Cardiovascular Strain in Older Adults: A Randomized Crossover Trial. Environ Health Perspect. 2024 Feb;132(2):27003. doi: 10.1289/EHP13159. Epub 2024 Feb 8.

  PMID: 38329752 BACKGROUND

MeSH Terms

Conditions

Body Temperature Changes; Heat Stress Disorders; Occupational Stress; Motor Activity; Hyperthermia

Interventions

Salvage Therapy

Condition Hierarchy (Ancestors)

Signs and Symptoms; Pathological Conditions, Signs and Symptoms; Wounds and Injuries; Occupational Diseases; Stress, Psychological; Behavioral Symptoms; Behavior

Intervention Hierarchy (Ancestors)

Therapeutics

Central Study Contacts

Glen P Kenny, PhD

CONTACT

6135625800; gkenny@uottawa.ca

Study Design

• Study Type: interventional
• Phase: not applicable
• Allocation: RANDOMIZED
• Masking: SINGLE
• Who Masked: OUTCOMES ASSESSOR
• Purpose: BASIC SCIENCE
• Intervention Model: CROSSOVER
• Sponsor Type: OTHER
• Responsible Party: PRINCIPAL INVESTIGATOR
• PI Title: Full Professor, University Research Chair

Study Record Dates

• First Submitted: June 9, 2026
• First Posted: June 18, 2026
• Study Start: July 1, 2026
• Primary Completion (Estimated): June 30, 2027
• Study Completion (Estimated): August 31, 2027
• Last Updated: June 18, 2026

Record last verified: 2026-06

Locations

CA (1)