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Progressive Heat Exposure and Physiological Strain

25 septembre 2026 mis à jour par: Glen P. Kenny, University of Ottawa

Does a Progressively Warming Workday Alter Work Performed and Physiological Heat Strain in Middle-Aged and Older Men?

Occupational heat-stress guidelines are commonly based on the level of environmental heat exposure and are largely derived from studies conducted under constant environmental conditions. However, outdoor workers are typically exposed to dynamic conditions, with environmental heat often increasing progressively from morning to afternoon. Consequently, workers may experience substantially different patterns of heat exposure across the workday even when average daily heat exposure is equivalent. It remains unclear whether the temporal pattern of heat exposure influences the amount of work that can be performed or the physiological strain experienced during a workday. Understanding these responses is important for determining whether occupational heat-stress guidelines developed under constant laboratory conditions adequately protect workers exposed to progressively changing environmental conditions.

The primary objective of this study is to determine whether the temporal pattern of heat exposure influences work performed and physiological heat strain during a simulated occupational workday in healthy middle-aged and older men. Participants will complete two 9-hour simulated workdays consisting of a 4-hour morning work period, a 1-hour lunch break, and a 4-hour afternoon work period. During one trial, wet-bulb globe temperature (WBGT) will remain constant at 28°C throughout the workday, whereas during the other trial, WBGT will progressively increase from morning to afternoon to simulate the changing environmental conditions of a typical hot summer workday. Both trials will have the same mean daily WBGT of 28°C. Participants will perform moderate-intensity treadmill exercise, and measures including total work performed, core temperature, heart rate, and time to the initial stay-time threshold will be assessed to determine whether constant and progressively increasing heat exposures produce different physiological and work-performance responses across the workday.

Aperçu de l'étude

Statut

Pas encore de recrutement

Les conditions

Intervention / Traitement

Type d'étude

Interventionnel

Inscription (Estimé)

14

Phase

  • N'est pas applicable

Contacts et emplacements

Cette section fournit les coordonnées de ceux qui mènent l'étude et des informations sur le lieu où cette étude est menée.

Coordonnées de l'étude

  • Nom: Glen P Kenny, PhD
  • Numéro de téléphone: 4282 6135625800
  • E-mail: gkenny@uottawa.ca

Lieux d'étude

  • Canada
    • Ontario
      • Ottawa, Ontario, Canada, K1N 6N5
        • University of Ottawa
        • Contact:
          • Glen P Kenny, PhD
          • Numéro de téléphone: 4282 613-562-5800
          • E-mail: gkenny@uottawa.ca

Critères de participation

Les chercheurs recherchent des personnes qui correspondent à une certaine description, appelée critères d'éligibilité. Certains exemples de ces critères sont l'état de santé général d'une personne ou des traitements antérieurs.

Critère d'éligibilité

Âges éligibles pour étudier

45 ans à 65 ans (Adulte, Adulte plus âgé)

Accepte les volontaires sains

Oui

Sexes éligibles pour l'étude

Homme

La description

Inclusion Criteria:

  • 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)

Exclusion Criteria:

  • 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

Plan d'étude

Cette section fournit des détails sur le plan d'étude, y compris la façon dont l'étude est conçue et ce que l'étude mesure.

Comment l'étude est-elle conçue ?

Détails de conception

  • Objectif principal: Science basique
  • Répartition: Randomisé
  • Modèle interventionnel: Affectation croisée
  • Masquage: Aucun (étiquette ouverte)

Armes et Interventions

Groupe de participants / Bras
Intervention / Traitement
Expérimental: Constant Heat Exposure

Participants will complete a 9-hour simulated occupational workday consisting of a 4-hour morning work period, a 1-hour seated lunch-recovery period, and a 4-hour afternoon work period. Wet-bulb globe temperature (WBGT) will remain constant at 28°C throughout the workday. During each work period, participants will perform moderate-intensity treadmill walking at a metabolic heat production of approximately 200 W·m-2. Participants will initially work continuously until reaching the initial stay-time threshold, defined as a core temperature of 38.0°C or an increase of 1.0°C above pre-work baseline, whichever occurs first. Thereafter, participants will complete 45-min work and 15-min seated rest cycles for the remainder of the work period.
Autre: Constant Heat Exposure

Participants complete a simulated occupational workday under constant environmental conditions, with WBGT maintained at 28°C throughout the morning and afternoon work periods.
Expérimental: Progressively Increasing Heat Exposure

Participants will complete a 9-hour simulated occupational workday consisting of a 4-hour morning work period, a 1-hour seated lunch-recovery period, and a 4-hour afternoon work period. WBGT will progressively increase from morning to afternoon to simulate the changing environmental conditions of a hot summer workday, while maintaining a mean daily WBGT of 28°C. During each work period, participants will perform moderate-intensity treadmill walking at a metabolic heat production of approximately 200 W·m-2. Participants will initially work continuously until reaching the initial stay-time threshold, defined as a core temperature of 38.0°C or an increase of 1.0°C above pre-work baseline, whichever occurs first. Thereafter, participants will complete 45-min work and 15-min seated rest cycles for the remainder of the work period.
Autre: Progressively Increasing Heat Exposure

Participants complete a simulated occupational workday in which WBGT progressively increases from morning to afternoon while maintaining a mean daily WBGT of 28°C.

Que mesure l'étude ?

Principaux critères de jugement

Mesure des résultats
Description de la mesure
Délai
Total work performed
Délai: From the start to the end of the morning and afternoon work periods during each experimental trial (0-4 hours and 5-9 hours after the start of the trial, respectively).

Total work completed during each 240-minute morning and afternoon work period, expressed as cumulative minutes of treadmill walking. Each work period consists of an initial continuous walking phase until core temperature reaches 38.0°C or increases by 1.0°C above the pre-work baseline, whichever occurs first, followed by intermittent 45-min work and 15-min seated rest cycles.
From the start to the end of the morning and afternoon work periods during each experimental trial (0-4 hours and 5-9 hours after the start of the trial, respectively).

Mesures de résultats secondaires

Mesure des résultats
Description de la mesure
Délai
Initial stay time
Délai: During the initial continuous walking phase of each morning and afternoon work period.

Time, in minutes, from the start of continuous treadmill walking until the initial stay-time threshold is reached, defined as a core temperature of 38.0°C or an increase of 1.0°C above the pre-work baseline, whichever occurs first. Participants who do not reach the threshold during the 240-minute work period will be identified as not having reached the threshold within 240 min.
During the initial continuous walking phase of each morning and afternoon work period.
Core temperature
Délai: Continuously throughout each experimental trial, including the morning work period, lunch recovery, and afternoon work period.

Core temperature measured continuously using a rectal thermocouple temperature probe to assess thermoregulatory strain throughout the simulated workday.
Continuously throughout each experimental trial, including the morning work period, lunch recovery, and afternoon work period.
Average core temperature during work-rest cycles
Délai: During the work-rest cycles of each morning and afternoon work period.

Average core temperature during the intermittent 45-min work and 15-min seated rest cycles following attainment of the initial stay-time threshold.
During the work-rest cycles of each morning and afternoon work period.
Mean skin temperature
Délai: Assessed throughout each experimental trial, including the morning work period, lunch recovery, and afternoon work period.

Mean skin temperature calculated from temperatures measured at eight body sites using ISO 9886 weighting factors.
Assessed throughout each experimental trial, including the morning work period, lunch recovery, and afternoon work period.
Heart rate
Délai: Continuously throughout each experimental trial, including the morning work period, lunch recovery, and afternoon work period.

Heart rate measured continuously using a chest-strap heart rate monitor and expressed as absolute heart rate.
Continuously throughout each experimental trial, including the morning work period, lunch recovery, and afternoon work period.
Percentage of heart rate reserve
Délai: Throughout each experimental trial, including the morning work period, lunch recovery, and afternoon work period.

Heart rate expressed as a percentage of the participant's heart rate reserve to assess relative cardiovascular strain during heat exposure.
Throughout each experimental trial, including the morning work period, lunch recovery, and afternoon work period.
Systolic blood pressure
Délai: Assessed at predetermined intervals throughout each experimental trial.

Systolic blood pressure measured at the brachial artery using automated oscillometry. Three measurements obtained at approximately 1-min intervals will be averaged for analysis.
Assessed at predetermined intervals throughout each experimental trial.
Diastolic blood pressure
Délai: Assessed at predetermined intervals throughout each experimental trial.

Diastolic blood pressure measured at the brachial artery using automated oscillometry. Three measurements obtained at approximately 1-min intervals will be averaged for analysis.
Assessed at predetermined intervals throughout each experimental trial.
Heart rate variability: standard deviation of normal R-R intervals (SDNN)
Délai: Throughout each experimental trial.

Cardiac autonomic modulation assessed from consecutive R-R intervals obtained using a 5-lead Holter electrocardiogram to calculate the standard deviation of normal R-R intervals (SDNN), expressed in milliseconds.
Throughout each experimental trial.
Heart rate variability: root mean square of successive differences (RMSSD)
Délai: Throughout each experimental trial.

Cardiac autonomic modulation assessed from consecutive R-R intervals obtained using a 5-lead Holter electrocardiogram to calculate the root mean square of successive differences between adjacent normal R-R intervals (RMSSD), expressed in milliseconds.
Throughout each experimental trial.
Urine specific gravity
Délai: Assessed upon arrival before each experimental trial.

Urine specific gravity measured to assess hydration status upon arrival at the laboratory. Higher values indicate greater urine concentration, whereas lower values indicate lower urine concentration.
Assessed upon arrival before each experimental trial.
Fluid consumption
Délai: Throughout each experimental trial.

Cumulative fluid consumption determined from all fluid consumed during each experimental session.
Throughout each experimental trial.
Fluid loss from body mass change
Délai: Assessed at the end of each 240-minute morning and afternoon work period of each experimental trial.

Fluid loss calculated from changes in body mass during each daytime work exposure, corrected for food and fluid intake.
Assessed at the end of each 240-minute morning and afternoon work period of each experimental trial.
Thermal sensation
Délai: Assessed at baseline, every 10 min during initial continuous work, at attainment of the initial stay-time threshold, at the end of the work and recovery components of each work-rest cycle, and at the beginning and end of lunch recovery.

Thermal sensation assessed using an 8-point scale ranging from 0 (neutral) to 7 (extremely hot). Higher scores indicate a greater sensation of heat.
Assessed at baseline, every 10 min during initial continuous work, at attainment of the initial stay-time threshold, at the end of the work and recovery components of each work-rest cycle, and at the beginning and end of lunch recovery.
Thermal comfort
Délai: Assessed at baseline, every 10 min during initial continuous work, at attainment of the initial stay-time threshold, at the end of the work and recovery components of each work-rest cycle, and at the beginning and end of lunch recovery.

Thermal comfort assessed using the ISO 10551 scale ranging from 1 (comfortable) to 4 (very uncomfortable). Higher scores indicate greater thermal discomfort.
Assessed at baseline, every 10 min during initial continuous work, at attainment of the initial stay-time threshold, at the end of the work and recovery components of each work-rest cycle, and at the beginning and end of lunch recovery.
Thirst sensation
Délai: Assessed at baseline, every 10 min during initial continuous work, at attainment of the initial stay-time threshold, at the end of the work and recovery components of each work-rest cycle, and at the beginning and end of lunch recovery.

Thirst sensation assessed using a 9-point scale ranging from 1 (not thirsty at all) to 9 (very, very thirsty). Higher scores indicate greater perceived thirst
Assessed at baseline, every 10 min during initial continuous work, at attainment of the initial stay-time threshold, at the end of the work and recovery components of each work-rest cycle, and at the beginning and end of lunch recovery.
Affective state
Délai: Assessed at baseline, every 10 min during initial continuous work, at attainment of the initial stay-time threshold, at the end of the work and recovery components of each work-rest cycle, and at the beginning and end of lunch recovery.

Affective state will be assessed using the 11-point Feeling Scale ranging from -5 (very bad) to +5 (very good), with 0 representing neutral. Higher scores indicate more positive affective state.
Assessed at baseline, every 10 min during initial continuous work, at attainment of the initial stay-time threshold, at the end of the work and recovery components of each work-rest cycle, and at the beginning and end of lunch recovery.
Perceived arousal
Délai: Assessed at baseline, every 10 min during initial continuous work, at attainment of the initial stay-time threshold, at the end of the work and recovery components of each work-rest cycle, and at the beginning and end of lunch recovery.

Perceived arousal assessed using a 7-point scale ranging from 1 (low arousal) to 7 (high arousal). Higher scores indicate greater perceived arousal.
Assessed at baseline, every 10 min during initial continuous work, at attainment of the initial stay-time threshold, at the end of the work and recovery components of each work-rest cycle, and at the beginning and end of lunch recovery.
Rating of perceived exertion
Délai: Assessed at baseline, every 10 min during initial continuous work, at attainment of the initial stay-time threshold, and at the end of the work and recovery components of each work-rest cycle.

Perceived exertion assessed using the Borg Rating of Perceived Exertion scale ranging from 6 (no exertion at all) to 20 (maximal exertion). Higher scores indicate greater perceived exertion.
Assessed at baseline, every 10 min during initial continuous work, at attainment of the initial stay-time threshold, and at the end of the work and recovery components of each work-rest cycle.
Environmental Symptoms Questionnaire-IV (ESQ-IV) total symptom score
Délai: Assessed at baseline and following completion of each experimental trial.

Symptoms associated with heat exposure will be assessed using the Environmental Symptoms Questionnaire-IV (ESQ-IV). Responses will be combined to generate a total symptom score, with higher scores indicating greater environmental symptom burden.
Assessed at baseline and following completion of each experimental trial.
Profile of Mood States-40 (POMS-40) total mood disturbance score
Délai: Assessed at baseline and following completion of each experimental trial.

Mood state will be assessed using the abbreviated 40-item Profile of Mood States questionnaire (POMS-40). Responses will be used to calculate a total mood disturbance score, with higher scores indicating greater overall mood disturbance.
Assessed at baseline and following completion of each experimental trial.
Changes in plasma volume
Délai: Assessed as baseline, and following each 240-minute morning and afternoon work period.

Change in plasma volume from baseline values calculated from duplicate measurements of hemoglobin and hematocrit at the start and end of each exposure using the technique by Dill and Costill.
Assessed as baseline, and following each 240-minute morning and afternoon work period.

Collaborateurs et enquêteurs

C'est ici que vous trouverez les personnes et les organisations impliquées dans cette étude.

Parrainer

University of Ottawa

Dates d'enregistrement des études

Ces dates suivent la progression des dossiers d'étude et des soumissions de résultats sommaires à ClinicalTrials.gov. Les dossiers d'étude et les résultats rapportés sont examinés par la Bibliothèque nationale de médecine (NLM) pour s'assurer qu'ils répondent à des normes de contrôle de qualité spécifiques avant d'être publiés sur le site Web public.

Dates principales de l'étude

Début de l'étude (Estimé)

1 octobre 2026

Achèvement primaire (Estimé)

30 juin 2027

Achèvement de l'étude (Estimé)

31 août 2027

Dates d'inscription aux études

Première soumission

18 septembre 2026

Première soumission répondant aux critères de contrôle qualité

25 septembre 2026

Première publication (Réel)

29 septembre 2026

Mises à jour des dossiers d'étude

Dernière mise à jour publiée (Réel)

29 septembre 2026

Dernière mise à jour soumise répondant aux critères de contrôle qualité

25 septembre 2026

Dernière vérification

1 septembre 2026

Plus d'information

Termes liés à cette étude

Mots clés

Termes MeSH pertinents supplémentaires

Autres numéros d'identification d'étude

  • HEPRU-2026-09-A

Informations sur les médicaments et les dispositifs, documents d'étude

Étudie un produit pharmaceutique réglementé par la FDA américaine

Non

Étudie un produit d'appareil réglementé par la FDA américaine

Non

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