Does a Progressively Warming Workday Alter Work Performed and Physiological Heat Strain in Middle-Aged and Older Men?
试验速览
- 阶段
- 不适用
- 状态
- 尚未招募
- 入组人数
- 14
- 试验地点
- 1
- 主要终点
- Total work performed
研究概览
简要总结
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.
研究设计
- 研究类型
- Interventional
- 分配方式
- Randomized
- 干预模型
- Crossover
- 主要目的
- Basic Science
- 盲法
- None
入排标准
- 年龄范围
- 45 Years 至 65 Years（Adult, Older Adult）
- 性别
- Male
- 接受健康志愿者
- 是
入选标准
- •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)
排除标准
- •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
研究组 & 干预措施
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.
干预措施: Constant Heat Exposure (Other)
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.
干预措施: Progressively Increasing Heat Exposure (Other)
结局指标
主要结局
Total work performed
时间窗: 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.
次要结局
- Initial stay time(During the initial continuous walking phase of each morning and afternoon work period.)
- Core temperature(Continuously throughout each experimental trial, including the morning work period, lunch recovery, and afternoon work period.)
- Average core temperature during work-rest cycles(During the work-rest cycles of each morning and afternoon work period.)
- Mean skin temperature(Assessed throughout each experimental trial, including the morning work period, lunch recovery, and afternoon work period.)
- Heart rate(Continuously throughout each experimental trial, including the morning work period, lunch recovery, and afternoon work period.)
- Percentage of heart rate reserve(Throughout each experimental trial, including the morning work period, lunch recovery, and afternoon work period.)
- Systolic blood pressure(Assessed at predetermined intervals throughout each experimental trial.)
- Diastolic blood pressure(Assessed at predetermined intervals throughout each experimental trial.)
- Heart rate variability: standard deviation of normal R-R intervals (SDNN)(Throughout each experimental trial.)
- Heart rate variability: root mean square of successive differences (RMSSD)(Throughout each experimental trial.)
- Urine specific gravity(Assessed upon arrival before each experimental trial.)
- Fluid consumption(Throughout each experimental trial.)
- Fluid loss from body mass change(Assessed at the end of each 240-minute morning and afternoon work period of each experimental trial.)
- Thermal sensation(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 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 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(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 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(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(Assessed at baseline and following completion of each experimental trial.)
- Profile of Mood States-40 (POMS-40) total mood disturbance score(Assessed at baseline and following completion of each experimental trial.)
- Changes in plasma volume(Assessed as baseline, and following each 240-minute morning and afternoon work period.)
研究者
Glen P. Kenny
Full Professor, University Research Chair
University of Ottawa