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

University of Ottawa

Status: Enrolling

Conditions: Cognitive Change; Physiological Stress; Heat Stress

Treatments: Other: Simulated indoor temperature upper limit

Study type: Interventional

Funder types: Other

Identifiers

NCT07267598

HEPRU-2025-10B

Details and patient eligibility

About

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.

Enrollment: 10 estimated patients

Sex: All

Ages: 18 to 29 years old

Volunteers: No Healthy Volunteers

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

Trial design

Primary purpose: Basic Science

Allocation: Randomized

Interventional model: Crossover Assignment

Masking: Single Blind

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10 participants in 2 patient groups

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

Experimental group

Description:

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).

Treatment:

Other: Simulated indoor temperature upper limit

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

Experimental group

Description:

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).

Treatment:

Other: Simulated indoor temperature upper limit