Suitability of a 26 °C Indoor Environment for Mitigating Heat Strain in Young Adults

NCT ID: NCT07267598

Last Updated: 2025-12-11

Basic Information

• Recruitment Status: RECRUITING
• Clinical Phase: NA
• Total Enrollment: 10 participants
• Study Classification: INTERVENTIONAL
• Study Start Date: 2025-11-07
• Study Completion Date: 2026-06-13

Brief Summary

While an indoor upper temperature limit of 26 °C has been shown to protect heat-vulnerable older adults (DOI: 10.1289/EHP11651), this guideline has not been verified in young, habitually active adults. Public health recommendations during hot weather typically emphasize staying in cool environments, avoiding strenuous activity, wearing lightweight clothing, and maintaining adequate hydration. However, young adults may be less likely to follow these guidelines. They often do not reduce their physical activity during extreme heat events and may overdress for fashion, cultural, or religious reasons. These behaviors can impose an additional thermoregulatory burden and lead to greater physiological strain during heat exposure, even though young adults generally have a higher capacity for heat dissipation than older individuals. Accordingly, it is important to evaluate whether an indoor temperature limit of 26 °C is sufficient to protect young, habitually active adults.

To address this gap, the investigators aim to assess changes in body temperature and cardiovascular strain in young, habitually active adults (18-29 years) during an 8-hour exposure to the recommended indoor upper temperature limit of 26 °C and 45% relative humidity (humidex of 29, considered comfortable). Participants will complete two conditions:

A) seated rest while dressed in light clothing (T-shirt, shorts, and socks), and B) light exercise (stepping to simulate activities of daily living, 4-4.5 METs) performed once per hour (except for the lunch hour) while dressed in light clothing plus an additional insulating layer (sweatshirt and sweatpants).

This experimental design will allow investigators to determine the effects of added clothing insulation and light activity-representative of typical daily behaviors-on physiological strain in young adults, and to assess whether refinements to the recommended 26 °C indoor temperature limit are warranted for this population.

Conditions

Heat Stress; Physiological Stress; Cognitive Change

Study Design

• Allocation Method: RANDOMIZED
• Intervention Model: CROSSOVER
• Primary Study Purpose: BASIC_SCIENCE
• Blinding Strategy: SINGLE

Study Groups

Exposure to indoor temperature upper limit without physical activity and added clothing.

Participants, dressed in light clothing (t-shirt, shorts and socks), perform seated rest while exposed daylong (8 hours) to an indoor temperature maintained at 26°C and 45% relative humidity (humidex equivalent of 29).

Group Type: EXPERIMENTAL

Simulated indoor temperature upper limit

Intervention Type: OTHER

Young adults exposed to an 8-hour simulated exposure.

Exposure to indoor temperature upper limit with physical activity and added clothing.

Participants, dressed in light clothing (t-shirt, shorts and socks) and an added clothing layer (sweatshirt and sweatpants), perform light exercise (i.e., stepping, representing activities of daily living, 4-4.5 METS) every hour (with exception of lunch hour) while exposed daylong (8 hours) to an indoor temperature maintained at 26°C and 45% relative humidity (humidex equivalent of 29).

Group Type: EXPERIMENTAL

Simulated indoor temperature upper limit

Intervention Type: OTHER

Young adults exposed to an 8-hour simulated exposure.

Interventions

Simulated indoor temperature upper limit

Young adults exposed to an 8-hour simulated exposure.

Intervention Type: OTHER

Eligibility Criteria

Inclusion Criteria

• Non-smoking.
• English or French speaking.
• Ability to provide informed consent.
• Healthy young adults without chronic disease (e.g., type 1 diabetes, hypertension)

Exclusion Criteria

• Endurance trained (i.e., engaged in regular physical training activities more than 3 times a week for more than 1 hour per session).
• Undergoing passive heat exposures such as regular of saunas, warm-water immersion, other.
• Use of or changes in medication judged by the patient or investigators to make participation in this study inadvisable.
• Current pregnancy

• Minimum Eligible Age: 18 Years
• Maximum Eligible Age: 29 Years
• Eligible Sex: ALL
• Accepts Healthy Volunteers: No

Sponsors

University of Ottawa

OTHER

Sponsor Role: lead

Responsible Party

Glen P. Kenny

Professor and University Research Chair

Responsibility Role: PRINCIPAL_INVESTIGATOR

Principal Investigators

Glen P Kenny, PhD

Role: PRINCIPAL_INVESTIGATOR

University of Ottawa

Locations

University of Ottawa

Ottawa, Ontario, Canada

Site Status: RECRUITING

Countries

Canada

Central Contacts

Glen P Kenny, PhD

Role: CONTACT

gkenny@uottawa.ca

6133029267 ext. 4282

Facility Contacts

Glen P Kenny, PhD

Role: primary

gkenny@uottawa.ca

613-562-5800 ext. 4282

Other Identifiers

HEPRU-2025-10B

Identifier Type: -

Identifier Source: org_study_id