Suitability of a 26 °C Indoor Environment for Mitigating Heat Strain in Young Adults
Trial statusRecruiting
Trial phaseNot applicable
Trial typeInterventional
Biological sexAll
Age18-29
SponsorUniversity of Ottawa
About this trial
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.
Eligibility criteria
This trial does not accept healthy volunteersQualifiers
Non-smoking.
English or French speaking.
Ability to provide informed consent.
Healthy young adults without chronic disease (e.g., type 1 diabetes, hypertension)
Disqualifiers
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
Design model
Crossover
Treatments tested in this trial
Simulated indoor temperature upper limit
Other interventionYoung adults exposed to an 8-hour simulated exposure.
Treatment groups
10 Participants
are divided into 2 treatment groupsGroup A: Exposure to indoor temperature upper limit without physical activity and added clothing.Experimental treatment 1 intervention
Group B: Exposure to indoor temperature upper limit with physical activity and added clothing.Experimental treatment 1 intervention
Trial outcomes
Primary outcomes
1
Core temperature (Peak) during daylong exposure to indoor temperature limit.
Peak rectal temperature (15 min average) during exposure. Rectal temperature is measured continuously throughout the 8 hour exposure to the simulated indoor temperature upper limit.
Time frame
End of 8 hour daylong exposure2
Core temperature (AUC) during daylong exposure to indoor temperature limit.
Areas under the curve (AUC) of rectal temperature during the 8 hour exposure to the simulate indoor temperature upper limit.
Time frame
End of 8 hour daylong exposure3
Core temperature end of daylong exposure to indoor temperature limit.
Rectal temperature measured at hour 8 of exposure to indoor temperature limit (15-min average).
Time frame
End of 8 hour daylong exposure4
Mean skin temperature (Peak) during daylong exposure to indoor temperature limit.
Peak mean skin temperature (15 min average) during exposure. Mean skin temperature as calculated from skin temperature measured across 7 body regions is measured continuously throughout the 8 hour exposure to the simulated indoor temperature upper limit.
Time frame
End of 8 hour daylong exposureSecondary outcomes
1
Profiles of Mood States (POMS) during daylong exposure to indoor temperature limit.
Potential changes in mood (7 subscales of mood: tension, anger, depression, fatigue, confusion, vigor and esteem related affect). The POMS-40 is a validated, self-administered questionnaire that examines seven distinct aspects of mood state across two positive subscales (Esteem-Related Affect, and Vigor) and five negative subscales (Fatigue, Tension, Confusion, Anger, and Depression), which are described across 40 distinct adjectives. For each individual item, participants were asked to describe "how you feel right now" by responding using a 5-point Likert scale (0 = "Not at all", 1 = "A little", 2 = "Moderately", 3 = "Quite a lot", or 4 = "Extremely"). The values of items associated with a specific subscale (e.g., Fatigue) were summed to calculate its score.
Time frame
At the start (hour 0) and end of 8 hour daylong exposure2
Environmental Symptoms Questionnaire (ESQ) during daylong exposure to indoor temperature limit.
Self-reported environmental reactions and medical symptomatology associated with prolonged heat exposure. The ESQ-IV is a validated 68-item, self-administered questionnaire that has been used successfully in identifying symptomatology during exposure to a wide variety of environmental conditions, including heat exposure \[24, 25\]. Participants are asked to assess and described "how you have been feeling today" by responding to each item using a 6-point Likert scale (0 = "Not at all", 1 = "Slight", 2 = "Somewhat", 3 = "Moderate", 4 = "Quite a bit", or 5 = "Extreme"). Total Symptom Score was calculated from this data by taking the sum of the intensity ratings from all 68 individual items using reverse scores for the three positive items from the list ("I Felt Good", "I Felt Alert", and "I Felt Wide Awake").
Time frame
At the start (hour 0) and end of 8 hour daylong exposure3
Sleep quality and quantify assessment during daylong exposure to indoor temperature limit.
The Pittsburgh Sleep Quality Index (PSQI) is a self-report questionnaire that works by asking 19 questions about a person's sleep habits over the past month. It is scored by evaluating seven components: subjective sleep quality, sleep latency, sleep duration, habitual sleep efficiency, sleep disturbances, use of sleeping medication, and daytime dysfunction. Each component is scored from 0 to 3, and these are summed to create a global score from 0 to 21, where a higher score indicates poorer sleep quality.
Time frame
At the start of 8 hour daylong exposure.Sponsors and contacts
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Source ClinicalTrials.gov