NCT07847437 Progressive Heat Exposure and Physiological Strain

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This trial targets 14 participants in total. It began in 2026-10-22 with a primary completion date of 2027-06-30.

Brief Summary

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.

Eligibility Criteria

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

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